Copyright: Copyright © 1999 Stephen Michael Schimpf
Citation: Copyright © 1999 Stephen Michael Schimpf


Animation toolbar

The Animation toolbar is initially displayed across the top of the sky chart, below the menu bar and to the right of the View toolbar. It contains buttons that deal with changing the time, starting and stopping animation, and locking solar system objects to the center of the display.

Use the Animation Toolbar command on the View menu to display or hide the Animation toolbar.

To turn a docked toolbar into a floating toolbar, move the pointer over the empty area around the toolbar's buttons, press and hold down the mouse button, and then drag the pointer away, toward the center of the sky chart. When the toolbar's outline has changed shape and is where you want it, release the mouse button.

To turn a floating toolbar into a docked toolbar, move the pointer over the toolbar's title bar, press and hold down the mouse button, and then drag the pointer to any edge of the sky chart. When the toolbar's outline has changed shape and is where you want it, release the mouse button.

When you move the pointer over a toolbar button and wait a second you'll see the name of the button appear in a small ToolTip window. A short description of the button will also appear in the left part of the status bar.


One Day Earlier command (Animation toolbar)

Displays the sky as it appeared one day earlier.

One Day Earlier button

Click this button on the Animation toolbar to execute this command.


One Hour Earlier command (Animation toolbar)

Displays the sky as it appeared one hour earlier.

One Hour Earlier button

Click this button on the Animation toolbar to execute this command.


One Hour Later command (Animation toolbar)

Displays the sky as it will appear one hour later.

One Hour Later button

Click this button on the Animation toolbar to execute this command.


One Day Later command (Animation toolbar)

Displays the sky as it will appear one day later.

One Day Later button

Click this button on the Animation toolbar to execute this command.


Chart toolbar

The Chart toolbar is initially displayed along the bottom of the sky chart, above the status bar and to the left of the Search toolbar. It contains buttons that deal with displaying or hiding components of the sky chart.

Use the Chart Toolbar command on the View menu to display or hide the Chart toolbar.

To turn a docked toolbar into a floating toolbar, move the pointer over the empty area around the toolbar's buttons, press and hold down the mouse button, and then drag the pointer away, toward the center of the sky chart. When the toolbar's outline has changed shape and is where you want it, release the mouse button.

To turn a floating toolbar into a docked toolbar, move the pointer over the toolbar's title bar, press and hold down the mouse button, and then drag the pointer to any edge of the sky chart. When the toolbar's outline has changed shape and is where you want it, release the mouse button.

When you move the pointer over a toolbar button and wait a second you'll see the name of the button appear in a small ToolTip window. A short description of the button will also appear in the left part of the status bar.


Stars command (Chart toolbar)

Use this command to display or hide stars. The registered version of CyberSky can display 80,179 stars to magnitude 8.5, whereas the shareware version can display only 1,671 stars to magnitude 5.0.

Stars button

Click this button on the Chart toolbar to execute this command.

Use the Stars command on the Chart menu to set star display options.


Star Labels command (Chart toolbar)

Use this command to display or hide star labels. CyberSky can label stars with their proper names (for example, "Betelgeuse" and "Rigel"), Bayer letters ("α" for Betelgeuse and "β" for Rigel), Flamsteed numbers ("58" for Betelgeuse and "19" for Rigel), or magnitudes ("0.5" for Betelgeuse and "0.12" for Rigel).

Star Labels button

Click this button on the Chart toolbar to execute this command.

Use the Stars command on the Chart menu to set star display options.


Constellation Figures command (Chart toolbar)

Use this command to display or hide constellation figures.

Constellation Figures button

Click this button on the Chart toolbar to execute this command.

Use the Constellations command on the Chart menu to set constellation display options.


Constellation Boundaries command (Chart toolbar)

Use this command to display or hide constellation boundaries.

Constellation Boundaries button

Click this button on the Chart toolbar to execute this command.

Use the Constellations command on the Chart menu to set constellation display options.


Constellation Labels command (Chart toolbar)

Use this command to display or hide constellation labels.

Constellation Labels button

Click this button on the Chart toolbar to execute this command.

Use the Constellations command on the Chart menu to set constellation display options.


Deep Sky Objects command (Chart toolbar)

Use this command to display or hide deep sky objects. The registered version of CyberSky can display 472 deep sky objects to magnitude 8.5, whereas the shareware version can display only 68 deep sky objects to magnitude 5.0.

Deep Sky Objects button

Click this button on the Chart toolbar to execute this command.

Use the Deep Sky Objects command on the Chart menu to set deep sky object display options.


Deep Sky Object Labels command (Chart toolbar)

Use this command to display or hide deep sky object labels.

Deep Sky Object Labels button

Click this button to execute this command.

Use the Deep Sky Objects command on the Chart menu to set deep sky object display options.


Solar System Objects command (Chart toolbar)

Use this command to display or hide solar system objects.

Solar System Objects button

Click this button on the Chart toolbar to execute this command.

Use the Solar System Objects command on the Chart menu to set solar system object display options.


Solar System Object Labels command (Chart toolbar)

Use this command to display or hide solar system object labels.

Solar System Object Labels button

Click this button on the Chart toolbar to execute this command.

Use the Solar System Objects command on the Chart menu to set solar system object display options.


Equatorial Grid command (Chart toolbar)

Use this command to display or hide equatorial coordinate system grid lines.

Equatorial Grid button

Click this button on the Chart toolbar to execute this command.


Horizontal Grid command (Chart toolbar)

Use this command to display or hide horizontal coordinate system grid lines.

Horizontal Grid button

Click this button on the Chart toolbar to execute this command.


Ecliptic command (Chart toolbar)

Use this command to display or hide the ecliptic. When the ecliptic is displayed, a cross labeled "NEP" marks the position of the north ecliptic pole, and another one labeled "SEP" marks the position of the south ecliptic pole.

Ecliptic button

Click this button on the Chart toolbar to execute this command.


Celestial Equator command (Chart toolbar)

Use this command to display or hide the celestial equator. When the celestial equator is displayed, a cross labeled "NCP" marks the position of the north celestial pole, and another one labeled "SCP" marks the position of the south celestial pole.

Celestial Equator button

Click this button on the Chart toolbar to execute this command.


Galactic Equator command (Chart toolbar)

Use this command to display or hide the galactic equator. When the galactic equator is displayed, a cross labeled "NGP" marks the position of the north galactic pole, and another one labeled "SGP" marks the position of the south galactic pole.

Galactic Equator button

Click this button on the Chart toolbar to execute this command.


Constellations listed alphabetically

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

This list contains all constellations arranged alphabetically.

A

Andromeda

Antlia

Apus

Aquarius

Aquila

Ara

Aries

Auriga

B

Bootes

C

Caelum

Camelopardalis

Cancer

Canes Venatici

Canis Major

Canis Minor

Capricornus

Carina

Cassiopeia

Centaurus

Cepheus

Cetus

Chamaeleon

Circinus

Columba

Coma Berenices

Corona Australis

Corona Borealis

Corvus

Crater

Crux

Cygnus

D

Delphinus

Dorado

Draco

E

Equuleus

Eridanus

F

Fornax

G

Gemini

Grus

H

Hercules

Horologium

Hydra

Hydrus

I

Indus

L

Lacerta

Leo

Leo Minor

Lepus

Libra

Lupus

Lynx

Lyra

M

Mensa

Microscopium

Monoceros

Musca

N

Norma

O

Octans

Ophiuchus

Orion

P

Pavo

Pegasus

Perseus

Phoenix

Pictor

Pisces

Piscis Austrinus

Puppis

Pyxis

R

Reticulum

S

Sagitta

Sagittarius

Scorpius

Sculptor

Scutum

Serpens

Sextans

T

Taurus

Telescopium

Triangulum

Triangulum Australe

Tucana

U

Ursa Major

Ursa Minor

V

Vela

Virgo

Volans

Vulpecula


Constellations listed by category

Arthropods | Birds | Fish | Geographical features | Mammals | Monsters | Objects | People | Reptiles

This list contains all constellations arranged by catagory.

Arthropods

Cancer

Musca

Scorpius

Birds

Apus

Aquila

Columba

Corvus

Cygnus

Grus

Pavo

Phoenix

Tucana

Fish

Dorado

Pisces

Piscis Austrinus

Volans

Geographical features

Eridanus

Mensa

Mammals

Aries

Camelopardalis

Canes Venatici

Canis Major

Canis Minor

Cetus

Delphinus

Equuleus

Leo

Leo Minor

Lepus

Lupus

Lynx

Taurus

Ursa Major

Ursa Minor

Vulpecula

Monsters

Capricornus

Centaurus

Draco

Hydra

Monoceros

Pegasus

Sagittarius

Objects

Antlia

Ara

Caelum

Carina

Circinus

Corona Australis

Corona Borealis

Crater

Crux

Fornax

Horologium

Libra

Lyra

Microscopium

Norma

Octans

Puppis

Pyxis

Reticulum

Sagitta

Scutum

Sextans

Telescopium

Triangulum

Triangulum Australe

Vela

People

Andromeda

Aquarius

Auriga

Bootes

Cassiopeia

Cepheus

Coma Berenices

Gemini

Hercules

Indus

Ophiuchus

Orion

Perseus

Pictor

Sculptor

Virgo

Reptiles

Chamaeleon

Hydrus

Lacerta

Serpens


Constellations listed by month

January | February | March | April | May | June | July | August | September | October | November | December

This list contains all constellations arranged by the months during which they are best seen.

January

Caelum

Dorado

Mensa

Orion

Reticulum

Taurus

February

Auriga

Camelopardalis

Canis Major

Columba

Gemini

Lepus

Monoceros

Pictor

March

Cancer

Canis Minor

Carina

Lynx

Puppis

Pyxis

Vela

Volans

April

Antlia

Chamaeleon

Crater

Hydra

Leo

Leo Minor

Sextans

Ursa Major

May

Canes Venatici

Centaurus

Coma Berenices

Corvus

Crux

Musca

Virgo

June

Bootes

Circinus

Libra

Lupus

Ursa Minor

July

Apus

Ara

Corona Borealis

Draco

Hercules

Norma

Ophiuchus

Scorpius

Serpens

Triangulum Australe

August

Corona Australis

Lyra

Sagittarius

Scutum

Telescopium

September

Aquila

Capricornus

Cygnus

Delphinus

Equuleus

Indus

Microscopium

Pavo

Sagitta

Vulpecula

October

Aquarius

Cepheus

Grus

Lacerta

Octans

Pegasus

Piscis Austrinus

November

Andromeda

Cassiopeia

Phoenix

Pisces

Sculptor

Tucana

December

Aries

Cetus

Eridanus

Fornax

Horologium

Hydrus

Perseus

Triangulum


Andromeda (And)

Names

Latin name	Andromeda

Genitive form	Andromedae

English name	Andromeda

German name	Andromeda

Area

Andromeda covers about 722 square degrees.

Named stars

Alpheratz	21 And	α And

Mirach	43 And	β And

Almach	57 And	γ1 And

History and mythology

Princess Andromeda was the beautiful daughter of King Cepheus of Ethiopia and the beautiful but vein Queen Cassiopeia.

Cassiopeia boasted that she and her daughter were more beautiful than any of the Nereids, fifty sea nymphs that were daughters of the god Nereus. This offended Poseidon, the god of the sea, who was married to the Neried Amphitrite. All the Nereids asked Poseidon to punish Cassiopeia, so he sent the sea monster Cetus to attack Ethiopia. An oracle told Cepheus that in order to appease the god of the sea and save his kingdom, he had to chain Andromeda to a rock by the seashore to await being devoured by Cetus as a human sacrifice.

Cepheus did what was necessary to save his kingdom, but the hero Perseus appeared to save Andromeda. Perseus had earlier beheaded Medusa, and now used her head as a weapon against the sea monster. Medusa was a gorgon, a creature so hideous that anyone who looked at her was turned to stone. When Cetus saw the head of Medusa he turned to stone and Andromeda was spared. After rescuing Andromeda from the sea monster, Perseus married her and presented the gorgon's head to the goddess Athena.

Cassiopeia, however, could not escape punishment. She was placed in the sky, forever circling the celestial pole, half the time hanging upside down.


Antlia (Ant)

Names

Latin name	Antlia

Genitive form	Antliae

English name	Air Pump

German name	Luftpumpe

Area

Antlia covers about 239 square degrees.

History and mythology

Antlia is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille originally called this constellation Machine Pneumatique after the air pump invented by Robert Boyle. This French name was Latinized as Machina Pneumatica or Antlia Pneumatica and was eventually shortened to the name we use today.


Apus (Aps)

Names

Latin name	Apus

Genitive form	Apodis

English name	Bird of Paradise

German name	Paradiesvogel

Area

Apus covers about 206 square degrees.

History and mythology

Apus is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the Southern Hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Apus is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.


Aquarius (Aqr)

Names

Latin name	Aquarius

Genitive form	Aquarii

English name	Water Bearer

German name	Wassermann

Area

Aquarius covers about 980 square degrees.

Named stars

Sadalmelik	34 Aqr	α Aqr

Sadalsuud	22 Aqr	β Aqr

Sadalachbia	48 Aqr	γ Aqr

Skat	76 Aqr	δ Aqr

Albali	2 Aqr	ε Aqr

Ancha	43 Aqr	θ Aqr

History and mythology

Aquarius represents Ganymede, the son of a king. One day, while watching over a herd of his father's sheep, he was spotted by Zeus. The king of the gods was so impressed with the boy's beauty that he sent an eagle to carry the boy away. Ganymede was carried off to Mount Olympus where he became the official cupbearer of the gods and poured water and wine for them.

Aquarius is known to be a very ancient constellation. Aquarius is found in the part of the sky known as the Sea in ancient Babylon. The Sea consisted of Aquarius and the surrounding constellations which all are associated with water or rain. It has been suggested that the reason for this aquatic theme is that the sun passes through this part of the sky during the rainy season.

The stars γ (Sadalachbia), η, π, and ζ form an asterism called the Water Jar.


Aquila (Aql)

Names

Latin name	Aquila

Genitive form	Aquilae

English name	Eagle

German name	Adler

Area

Aquila covers about 653 square degrees.

Named stars

Altair	53 Aql	α Aql

Alshain	60 Aql	β Aql

Tarazed	50 Aql	γ Aql

History and mythology

Aquila represents the eagle sent by Zeus to carry off the shepherd boy Ganymede to become the official cupbearer of the gods. Hebe, the goddess of youth, had held this position until her marriage and Zeus needed to find a replacement. One day, while Ganymede watched over a herd of his father's sheep, Zeus spotted him. The king of the gods was so impressed with the boy's beauty that he sent an eagle to carry the boy away to Mount Olympus.

Altair, Deneb in Cygnus, and Vega in Lyra form an asterism called the Summer Triangle.


Ara (Ara)

Names

Latin name	Ara

Genitive form	Arae

English name	Altar

German name	Altar

Area

Ara covers about 237 square degrees.

History and mythology

Ara was originally called Ara Centauri, the centaur's altar, after the altar of Chiron, the centaur represented by the constellation Centaurus. Chiron is said to have sacrificed a wolf, represented by the constellation Lupus, on this altar.


Aries (Ari)

Names

Latin name	Aries

Genitive form	Arietis

English name	Ram

German name	Widder

Area

Aries covers about 441 square degrees.

Named stars

Hamal	13 Ari	α Ari

Sheratan	6 Ari	β Ari

Mesarthim	5 Ari	γ2 Ari

History and mythology

Aries represents the golden ram whose fleece was sought by Jason and the Argonauts.

The vernal equinox, the point at which the sun crosses the celestial equator at the beginning of spring, was originally located in Aries. Due to the precession of the equinoxes, this point has moved into the constellation Pisces, but it is still referred to as the "first point of Aries". In about 600 years the vernal equinox will move into the constellation Aquarius.


Auriga (Aur)

Names

Latin name	Auriga

Genitive form	Aurigae

English name	Charioteer

German name	Fuhrmann

Area

Auriga covers about 657 square degrees.

Named stars

Capella	13 Aur	α Aur

Menkalinan	34 Aur	β Aur

Alanz	7 Aur	ε Aur

History and mythology

Auriga represents Phaethon, the son of the sun god Helios, who wanted very much to drive the chariot of the sun across the sky. His father reluctantly agreed to let him drive the chariot for one day.

Handling the chariot was much harder than Phaethon had imagined. As the chariot climbed higher and higher in the sky he found it more and more difficult to control the four horses that drew the chariot. Phaethon soon lost control and the chariot was drawn all over the sky. It even grazed the earth, causing the land to burn the seas and rivers to evaporate. In order to stop this destruction, Zeus hurled lightning at Phaethon, who died and fell into the river Eridanus.

Auriga is also said to represent a herdsman tending a goat and her kids. The stars ε, ζ, and η Aurigae are sometimes called "the kids".


Bootes (Boo)

Names

Latin name	Bootes

Genitive form	Bootis

English name	Herdsman

German name	Bärenhüter

Area

Bootes covers about 907 square degrees.

Named stars

Arcturus	16 Boo	α Boo

Nekkar	42 Boo	β Boo

Seginus	27 Boo	γ Boo

Izar	36 Boo	ε Boo

Muphrid	8 Boo	η Boo

Alkalurops	51 Boo	μ1 Boo

History and mythology

Bootes represents a herdsman who circles the north celestial pole and thus keeps the animals in this region of the sky in their place.

In another story, Bootes represents Arcas, the son of Zeus and Callisto. Callisto liked to hunt and because a favorite of Artemis, the goddess of hunting. She swore a vow of chastity to the goddess, but gave birth to a son named Arcas as a result of being raped by Zeus, the king of the gods. Hera, the wife of Zeus, was very angry and changed Callisto into a bear.

Callisto roamed the woods for fifteen years in the form of a bear. One day she encountered her son, Arcas, who was in the woods hunting with his two dogs, Asterion and Chara. Arcas, not recognizing his mother in the form of a bear, was about to spear the bear, but Zeus prevented this tragedy by placing both mother and son in the sky. Callisto became the constellation Ursa Major and Arcas became the constellation Bootes. The gods placed the hunting dogs near Bootes as the constellation Canes Venatici.

Bootes is sometimes said to represent the inventor of the plough. Demeter, the goddess of agriculture, asked Zeus to honor that person by placing him in the sky.


Caelum (Cae)

Names

Latin name	Caelum

Genitive form	Caeli

English name	Chisel

German name	Grabstichel

Area

Caelum covers about 125 square degrees.

History and mythology

Caelum is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille named this constellation after the sculptor's chisel.


Camelopardalis (Cam)

Names

Latin name	Camelopardalis

Genitive form	Camelopardalis

English name	Giraffe

German name	Giraffe

Area

Camelopardalis covers about 757 square degrees.

History and mythology

Camelopardalis was invented by the Dutch and astronomer and cartographer Petrus Plancius (1552-1622). Plancius invented a number of new constellations, but only Camelopardalis, Columba, and Monoceros are still accepted today.

The German astronomer Jakob Bartsch included Camelopardalis on his star map published in 1624.


Cancer (Cnc)

Names

Latin name	Cancer

Genitive form	Cancri

English name	Crab

German name	Krebs

Area

Cancer covers about 506 square degrees.

Named stars

Acubens	65 Cnc	α Cnc

Altarf	17 Cnc	β Cnc

Asellus Borealis	43 Cnc	γ Cnc

Asellus Australis	47 Cnc	δ Cnc

History and mythology

To atone for killing his own children in a fit of madness caused by Hera, the queen of the gods, Heracles was ordered by the oracle at Delphi to serve king Euristeus of Mycenae. The king assigned twelve seemingly impossible tasks, or labors, for Heracles to perform. The second of these tasks was to kill the Hydra, a dog-like monster with nine heads and breath that could kill on contact.

Cancer represents the little crab sent by Hera to interfere in the battle between Heracles and the Hydra in the marsh of Lerna. The crab pinched Heracles' toes to distract him, and Heracles crushed the crab with his foot. Hera rewarded the little crab by placing it in the sky.


Canes Venatici (CVn)

Names

Latin name	Canes Venatici

Genitive form	Canum Venaticorum

English name	Hunting Dogs

German name	Jagdhunde

Area

Canes Venatici covers about 465 square degrees.

Named stars

Cor Caroli	12 CVn	α2 CVn

Chara	8 CVn	β CVn

History and mythology

Canes Venatici was named by the German astronomer Johannes Hevelius (1611-1687) in his influential star atlas Firmamentum Sobiescianum sive Uranographia, which was completed by his wife and published in 1690, after his death, in Danzig.

Hevelius named this constellation after the two hunting dogs, Astarion and Chara, held on a leash by the hunter Arcas, represented by the constellation Bootes.


Canis Major (CMa)

Names

Latin name	Canis Major

Genitive form	Canis Majoris

English name	Great Dog

German name	Großer Hund

Area

Canis Major covers about 380 square degrees.

Named stars

Sirius	9 CMa	α CMa

Mizam	2 CMa	β CMa

Wezen	25 CMa	δ CMa

Adhara	21 CMa	ε CMa

Furud	1 CMa	ζ CMa

Aludra	31 CMa	η CMa

History and mythology

Canis Major represents the larger of Orion's two hunting dogs. This constellation is also said to represent a large dog given to Europa, daughter of King Agenor of Phoenicia, by Zeus.

Canis Major contains Sirius, the brightest star in the sky other than the sun. Sirius is known as the "Dog Star" because it proceeded the period of hottest weather in the Northern Hemisphere, the "dog days" of summer. Sirius rises just before the sun in late July, but because of the precession of the equinoxes the star used to rise just before the sun earlier in the year, right after the start of summer. The ancient Egyptians would watch for the rising of Sirius to signal the beginning of summer and the annual flooding of the Nile River on which their civilization depended.

The ancient Egyptians associated Sirius with Isis, the sister and wife of Osiris, the god of the underworld. The southern shaft of the Queen's Chamber in the great pyramid of Khufu points directly at the meridian position of Sirius in 2450 BC.

Sirius, Procyon in Canis Minor, and Betelgeuse in Orion form an asterism called the Winter Triangle.


Canis Minor (CMi)

Names

Latin name	Canis Minor

Genitive form	Canis Minoris

English name	Little Dog

German name	Kleiner Hund

Area

Canis Minor covers about 183 square degrees.

Named stars

Procyon	10 CMi	α CMi

Gomeisa	3 CMi	β CMi

History and mythology

Canis Minor is usually thought to represent the smaller of Orion's two hunting dogs.

This constellation is also associated with Maera, the dog owned by Icarius. In Greek mythology Icarius was a mortal who had received the secret of wine making from the god Dionysus. One day a group of peasants blamed Icarius for giving them the wine that they thought had poisoned them. These peasants killed Icarius, and Maera ran home and guided Erigone, the daughter of Icarius, back to her father's body. Erigone was so upset at her father's murder that she killed herself. The gods took pity on the family and placed Icarius in the sky as the constellation Bootes; Erigone became the constellation Virgo, and the little dog Maera became the constellation Canis Minor.

Procyon, Sirius in Canis Major, and Betelgeuse in Orion form an asterism called the Winter Triangle.


Capricornus (Cap)

Names

Latin name	Capricornus

Genitive form	Capricorni

English name	Sea Goat

German name	Steinbock

Area

Capricornus covers about 414 square degrees.

Named stars

Algiedi	6 Cap	α2 Cap

Dabih	9 Cap	β Cap

Nashira	40 Cap	γ Cap

Deneb Algiedi	49 Cap	δ Cap

History and mythology

Capricornus is usually depicted as a goat with the tail of a fish, and is associated with the Greek god Pan. Pan was the son of Hermes, the messenger of the gods. He had the lower body of a goat and horns on his head.

During the battle in which the younger Olympian gods overthrew the older Titans a monster called Typhon attacked the Olympians. Pan warned the gods and they all turned themselves into animals to hide from the monster. Pan turned himself into a fish and hid in a river. It is this transformation that is represented by Capricornus.

Later, Pan and Hermes both helped Zeus when he was injured during his battle against Typhon. Zeus was eventually able to overcome Typhon with his lightning bolts, and he trapped the monster under Mount Etna. For his service Zeus placed an image of Pan in the sky.


Carina (Car)

Names

Latin name	Carina

Genitive form	Carinae

English name	Keel

German name	Kiel

Area

Carina covers about 494 square degrees.

Named stars

Canopus	α Car

Miaplacidus	β Car

Turais	ι Car

History and mythology

Carina was originally part of a large constellation named Argo Navis. That constellation represented the ship on which Jason and his companions, the Argonauts, made their journey in search of the Golden Fleece.

Argo Navis was split into the three constellations called Carina, Puppis, and Vela by the French astronomer Nicolas Louis de Lacaille (1713-1762) in his star map published in 1763. Argo Navis was eventually split into the four constellations called Carina, Puppis, Pyxis, and Vela when the International Astronomical Union defined the 88 modern constellations in 1930.


Cassiopeia (Cas)

Names

Latin name	Cassiopeia

Genitive form	Cassiopeiae

English name	Cassiopeia

German name	Kassiopeia

Area

Cassiopeia covers about 598 square degrees.

Named stars

Schedar	18 Cas	α Cas

Caph	11 Cas	β Cas

Ruchbah	37 Cas	δ Cas

History and mythology

Queen Cassiopeia was the beautiful but vein wife of King Cepheus of Ethiopia, and the mother of the beautiful Princess Andromeda.

Cassiopeia boasted that she and her daughter were more beautiful than any of the Nereids, fifty sea nymphs that were daughters of the god Nereus. This offended Poseidon, the god of the sea, who was married to the Neried Amphitrite. All the Nereids asked Poseidon to punish Cassiopeia, so he sent the sea monster Cetus to attack Ethiopia. An oracle told Cepheus that in order to appease the god of the sea and save his kingdom, he had to chain Andromeda to a rock by the seashore to await being devoured by Cetus as a human sacrifice.

Cepheus did what was necessary to save his kingdom, but the hero Perseus appeared to save Andromeda. Perseus had earlier beheaded Medusa, and now used her head as a weapon against the sea monster. Medusa was a gorgon, a creature so hideous that anyone who looked at her was turned to stone. When Cetus saw the head of Medusa he turned to stone and Andromeda was spared. After rescuing Andromeda from the sea monster, Perseus married her and presented the gorgon's head to the goddess Athena.

Cassiopeia, however, could not escape punishment. She was placed in the sky, forever circling the celestial pole, half the time hanging upside down.


Centaurus (Cen)

Names

Latin name	Centaurus

Genitive form	Centauri

English name	Centaur

German name	Zentaur

Area

Centaurus covers about 1060 square degrees.

Named stars

Rigelkent	α1 Cen

Hadar	β Cen

Menkent	5 Cen	θ Cen

History and mythology

Centaurus represents the centaur Chiron. Centaurs are creatures that have the body of a horse, but have the chest, arms, and head of a man. Most centaurs are barbaric creatures, known for their drunkenness.

Chiron was the son of the god Kronos and the nymph Philyra. Kronos disguised himself as a horse so that his affair with Philyra would not be discovered by his wife, Rhea. Chiron was therefore born as a centaur. Unlike most other centaurs, Chiron was a good and wise creature and he was immortal because his father was a god. He tutored the physician Asclepius, the strongman Heracles, and Jason, the leader of the Argonauts.

Heracles accidentally injured Chiron during a fight with other centaurs over a jar of wine. Chiron was immortal, so he could not die, and hence lived in terrible pain. He pleaded with he gods to end his suffering and let him die. Zeus did so, and placed him among the stars.


Cepheus (Cep)

Names

Latin name	Cepheus

Genitive form	Cephei

English name	Cepheus

German name	Kepheus

Area

Cepheus covers about 588 square degrees.

Named stars

Alderamin	5 Cep	α Cep

Alfirk	8 Cep	β Cep

Alrai	35 Cep	γ Cep

Alkurhah	17 Cep	ξ Cep

History and mythology

King Cepheus of Ethiopia was the husband of the beautiful but vein Queen Cassiopeia and the father of the beautiful Princess Andromeda.

Cassiopeia boasted that she and her daughter were more beautiful than any of the Nereids, fifty sea nymphs that were daughters of the god Nereus. This offended Poseidon, the god of the sea, who was married to the Neried Amphitrite. All the Nereids asked Poseidon to punish Cassiopeia, so he sent the sea monster Cetus to attack Ethiopia. An oracle told Cepheus that in order to appease the god of the sea and save his kingdom, he had to chain Andromeda to a rock by the seashore to await being devoured by Cetus as a human sacrifice.

Cepheus did what was necessary to save his kingdom, but the hero Perseus appeared to save Andromeda. Perseus had earlier beheaded Medusa, and now used her head as a weapon against the sea monster. Medusa was a gorgon, a creature so hideous that anyone who looked at her was turned to stone. When Cetus saw the head of Medusa he turned to stone and Andromeda was spared. After rescuing Andromeda from the sea monster, Perseus married her and presented the gorgon's head to the goddess Athena.

Cassiopeia, however, could not escape punishment. She was placed in the sky, forever circling the celestial pole, half the time hanging upside down.


Cetus (Cet)

Names

Latin name	Cetus

Genitive form	Ceti

English name	Whale

German name	Wal

Area

Cetus covers about 1,231 square degrees.

Named stars

Menkar	92 Cet	α Cet

Deneb Kaitos	16 Cet	β Cet

Baten Kaitos	55 Cet	ζ Cet

Mira	68 Cet	ο Cet

History and mythology

Cetus was the sea monster sent by Poseidon to devour Princess Andromeda of Ethiopia.

Queen Cassiopeia boasted that she and her daughter were more beautiful than any of the sea nymphs known as the Nereids. This offended Poseidon, the god of the sea, and as punishment Andromeda was chained to a rock by the seashore to await being devoured by the sea monster represented by the constellation Cetus.

The hero Perseus beheaded Medusa, and used her head as a weapon against the sea monster. Medusa was a gorgon, a creature so hideous that anyone who looked at her was turned to stone. When Cetus saw the head of Medusa he turned to stone and Andromeda was spared. After rescuing Andromeda from the sea monster, Perseus married her and presented the gorgon's head to the goddess Athena.


Chamaeleon (Cha)

Names

Latin name	Chamaeleon

Genitive form	Chamaeleontis

English name	Chameleon

German name	Chamäleon

Area

Chamaeleon covers about 132 square degrees.

History and mythology

Chamaeleon is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the Southern Hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Chamaeleon is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.


Circinus (Cir)

Names

Latin name	Circinus

Genitive form	Circini

English name	Compasses

German name	Zirkel

Area

Circinus covers about 93 square degrees.

History and mythology

Circinus is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille named this constellation after a pair of drawing compasses.


Columba (Col)

Names

Latin name	Columba

Genitive form	Columbae

English name	Dove

German name	Taube

Area

Columba covers about 270 square degrees.

Named stars

Phact	α Col

Wazen	β Col

History and mythology

Camelopardalis was invented by the Dutch and astronomer and cartographer Petrus Plancius (1552-1622). Plancius invented a number of new constellations, but only Camelopardalis, Columba, and Monoceros are still accepted today.

Columba is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.

Columba is said to represent the dove that guided Jason and the Argonauts through the treacherous waters at the entrance of the Black Sea.


Coma Berenices (Com)

Names

Latin name	Coma Berenices

Genitive form	Comae Berenices

English name	Berenice's Hair

German name	Haar der Berenike

Area

Coma Berenices covers about 387 square degrees.

History and mythology

According to one legend, Queen Berenice of Egypt was very worried about her husband, who had gone to lead the Egyptian armies in their fight against the Assyrians. Berenice promised the goddess of beauty that she would sacrifice her long, beautiful hair if she would bring the king safely back to Egypt. The king did return safely, and Berenice lived up to her promise. She cut off her hair and placed it in the temple of the goddess of beauty.

Not long thereafter, the king visited the temple because he wanted to see his wife's beautiful hair again. The king was told that the hair had mysteriously disappeared, but it was soon discovered what had happened. The gods were so pleased by Berenice's sacrifice that they placed her hair in the sky where the king could see it any time he wanted to.


Corona Australis (CrA)

Names

Latin name	Corona Australis

Genitive form	Coronae Australis

English name	Southern Crown

German name	Südliche Krone

Area

Corona Australis covers 128 square degrees.

History and mythology

Corona Australis is said to represent a crown worn by the centaur represented by the constellation Sagittarius. Corona Australis is also associated with Dionysus, the Greek god of wine.


Corona Borealis (CrB)

Names

Latin name	Corona Borealis

Genitive form	Coronae Borealis

English name	Northern Crown

German name	Nördliche Krone

Area

Corona Borealis covers about 179 square degrees.

Named stars

Alphecca	5 CrB	α CrB

Nusakan	3 CrB	β CrB

History and mythology

Corona Borealis represents a crown given to Ariadne, daughter of King Minos of Crete, as a wedding gift.

The aboriginal people of Australia associated this group of stars with the weapon called a boomerang.


Corvus (Crv)

Names

Latin name	Corvus

Genitive form	Corvi

English name	Crow

German name	Rabe

Area

Corvus covers about 184 square degrees.

Named stars

Alchibah	1 Crv	α Crv

Gienah	4 Crv	γ Crv

Algorab	7 Crv	δ Crv

History and mythology

The bird represented by the constellation Corvus was sent with a cup by the god Apollo to fetch water. The bird saw a fig tree and, wishing to eat the fruit, loitered at the tree and waited for the figs to become ripe.

After eating the ripe fruit the bird returned to Apollo with a water snake in his claws and explained that the snake was the reason he had taken so long to fetch the water. Apollo punished the bird for lying by placing it in the sky along with the cup and water snake represented by the constellations Crater and Hydra. The poor bird is doomed to everlasting thirst because the water snake controls the cup and its contents.


Crater (Crt)

Names

Latin name	Crater

Genitive form	Crateris

English name	Cup

German name	Becher

Area

Crater covers about 282 square degrees.

Named stars

Alkes	7 Crt	α Crt

History and mythology

During the battle in which the younger Olympian gods overthrew the older Titans a monster called Typhon attacked the Olympians. Pan warned the gods and they all turned themselves into animals to hide from the monster. The god Apollo turned himself into a crow, the bird that was considered sacred to him.

The crow represented by the constellation Corvus was sent with a cup by Apollo to fetch water. The bird saw a fig tree and, wishing to eat the fruit, loitered at the tree and waited for the figs to become ripe.

After eating the ripe fruit the bird returned to Apollo with a water snake in his claws and explained that the snake was the reason he had taken so long to fetch the water. Apollo punished the bird for lying by placing it in the sky along with the cup and water snake represented by the constellations Crater and Hydra. The poor bird is doomed to everlasting thirst because the water snake controls the cup and its contents.


Crux (Cru)

Names

Latin name	Crux

Genitive form	Crucis

English name	Southern Cross

German name	Kreuz des Südens

Area

Crux covers about 68 square degrees.

Named stars

Acrux	α1 Cru

Becrux	β Cru

Gacrux	γ Cru

History and mythology

Crux was originally called Crux Australis, the Southern Cross, to distinguish it from Cygnus, which is sometimes called the Northern Cross.


Cygnus (Cyg)

Names

Latin name	Cygnus

Genitive form	Cygni

English name	Swan

German name	Schwan

Area

Area	804 square degrees

Named stars

Deneb	50 Cyg	α Cyg

Albireo	6 Cyg	β1 Cyg

Sadir	37 Cyg	γ Cyg

History and mythology

Cygnus is an ancient constellation that has been associated with one type of bird or another by many cultures.

One legend says that Cygnus was a friend of Phaethon, the son of the sun god Helios, who wanted very much to drive the chariot of the sun across the sky. His father reluctantly agreed to let him drive the chariot for one day.

Handling the chariot was much harder than Phaethon had imagined. As the chariot climbed higher and higher in the sky he found it more and more difficult to control the four horses that drew the chariot. Phaethon soon lost control and the chariot was drawn all over the sky. It even grazed the earth, causing the land to burn the seas and rivers to evaporate. In order to stop this destruction, Zeus hurled lightning at Phaethon, who died and fell into the river Eridanus.

Cygnus dove into the river to try to rescue his friend. He swam from place to place, diving to try to find Phaethon's body. People said that Cygnus looked like a swan diving for food. The sun god Helios rewarded Cygnus for his friendship to his son by placing him in the sky as a swan.

Deneb, Altair in Aquila, and Vega in Lyra form an asterism called the Summer Triangle.


Delphinus (Del)

Names

Latin name	Delphinus

Genitive form	Delphini

English name	Dolphin

German name	Delphin

Area

Delphinus covers about 189 square degrees.

History and mythology

This constellation represents the dolphin that, according to Greek mythology, helped Poseidon marry Amphitrite. Poseidon, the god of the sea, wanted to marry Amphitrite, one of the sea nymphs knows as the Nereids, but she wanted nothing to do with him. Poseidon sent the dolphin to speak with Amphitrite and get her to change her mind. Amphitrite eventually agreed to marry Poseidon, and in gratitude the god placed the dolphin among the stars.

The stars α, β, γ, and δ form an asterism called Job's Coffin.


Dorado (Dor)

Names

Latin name	Dorado

Genitive form	Doradus

English name	Swordfish

German name	Schwertfisch

Area

Dorado covers about 179 square degrees.

History and mythology

Dorado is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the Southern Hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Dorado is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.

Although the Latin name of this constellation is translated as goldfish, the constellation is said to have originally represented the Hawaiian mahi mahi, and is now also commonly thought to represent a swordfish.


Draco (Dra)

Names

Latin name	Draco

Genitive form	Draconis

English name	Dragon

German name	Drache

Area

Draco covers about 1,083 square degrees.

Named stars

Thuban	11 Dra	α Dra

Rastaban	23 Dra	β Dra

Eltanin	33 Dra	γ Dra

Altais	57 Dra	δ Dra

Edasich	12 Dra	ι Dra

Giauzar	1 Dra	λ Dra

Alrakis	21 Dra	μ Dra

Grumium	32 Dra	ξ Dra

History and mythology

This constellation is associated with the dragon that, according to Greek mythology, guarded the golden apples kept in a garden on the slopes of Mount Atlas. When the gods Zeus and Hera were married, the bride gave three golden apples to Zeus as a wedding gift. Zeus kept the golden apples safe in the garden protected by a dragon named Ladon.

The strongman Heracles was sent to perform twelve seemingly impossible tasks, or labors, and the eleventh of these labors was to steal the golden apples. When he came to do so, he fought and killed the dragon using arrows poisoned with the blood of the Hydra. The gods placed the dragon in the sky as a reward for guarding the golden apples to his death.

A different version of this story says that the garden was owned by the god Atlas and that he was the only person allowed by Ladon to come near the golden apples. Atlas is the god who holds the world on his shoulders. Heracles is said to have to convinced Atlas to steal the golden apples for him, and promised to carry the world for a while. Zeus and Hera were very angry when they discovered that the golden apples had been stolen, and they punished the dragon Ladon by placing him in the cold northern skies.

The ancient Egyptians associated these stars with Taweret, the goddess of protection and fertility depicted as a hippopotamus.

The northern shaft of the King's Chamber in the Great Pyramid of Khufu at Giza points directly at the upper meridian position of Thuban, which was the pole star in 2450 BC.


Equuleus (Equ)

Names

Latin name	Equuleus

Genitive form	Equulei

English name	Little Horse

German name	Kleines Pferd

Area

Equuleus covers about 72 square degrees.

Named stars

Kitalpha	8 Equ	α Equ

History and mythology

Equuleus is said to represent a horse given as a gift to Castor by the god Hermes.


Eridanus (Eri)

Names

Latin name	Eridanus

Genitive form	Eridani

English name	Eridanus

German name	Eridanus

Area

Eridanus covers about 1,138 square degrees.

Named stars

Achernar	α Eri

Cursa	67 Eri	β Eri

Zaurak	34 Eri	γ Eri

Rana	23 Eri	δ Eri

Azha	3 Eri	ε Eri

Acamar	θ1 Eri

Beid	38 Eri	ο1 Eri

Keid	40 Eri	ο2 Eri

Angetenar	2 Eri	τ2 Eri

History and mythology

According to Greek mythology, Eridanus is the river into which Phaethon fell after he attempted to drive the chariot of the sun across the sky. Phaethon, the son of the sun god Helios, wanted very much to drive the chariot of the sun across the sky. His father reluctantly agreed to let him drive the chariot for one day.

Handling the chariot was much harder than Phaethon had imagined. As the chariot climbed higher and higher in the sky he found it more and more difficult to control the four horses that drew the chariot. Phaethon soon lost control and the chariot was drawn all over the sky. It even grazed the earth, causing the land to burn the seas and rivers to evaporate. In order to stop this destruction, Zeus hurled lightning at Phaethon, who died and fell into the river Eridanus.


Fornax (For)

Names

Latin name	Fornax

Genitive form	Fornacis

English name	Furnace

German name	Ofen

Area

Fornax covers about 398 square degrees.

History and mythology

Fornax is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille named this constellation Fornax Chemica, the chemical furnace, in honor of the French chemist Antoine Laurant Lavoisier, who was later executed during the French Revolution.


Gemini (Gem)

Names

Latin name	Gemini

Genitive form	Geminorum

English name	Twins

German name	Zwillinge

Area

Gemini covers about 514 square degrees.

Named stars

Castor	66 Gem	α Gem

Pollux	78 Gem	β Gem

Alhena	24 Gem	γ Gem

Wasat	55 Gem	δ Gem

Mebsuta	27 Gem	ε Gem

Mekbuda	43 Gem	ζ Gem

Tejat Prior	7 Gem	η Gem

Tejat Posterior	13 Gem	μ Gem

History and mythology

The constellation Gemini represents the twins Castor and Polydeuces, for which the two brightest stars in the constellation are named. According to Greek mythology, the twins are sons of the god Zeus and a mortal woman, Queen Leda of Sparta.

Castor, a mortal, excelled at hunting and boxing. Polydeuces, an immortal, was an accomplished horseman and taught swordfighting to Heracles.

Castor and Polydeuces accompanied the Argonauts in their quest for the Golden Fleece. During a quarrel with another set of twins, Castor was killed. Polydeuces was so upset at the loss of his brother that he asked Zeus to allow him to share his immortality with Caster. Zeus agreed and placed both brothers in the sky.


Grus (Gru)

Names

Latin name	Grus

Genitive form	Gruis

English name	Crane

German name	Kranich

Area

Grus covers about 366 square degrees.

Named stars

Alnair	α Gru

History and mythology

Grus is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the Southern Hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Grus is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.


Hercules (Her)

Names

Latin name	Hercules

Genitive form	Herculis

English name	Hercules

German name	Herkules

Area

Hercules covers about 1,225 square degrees.

Named stars

Rasalgethi	64 Her	α1 Her

Kornephoros	27 Her	β Her

Sarin	65 Her	δ Her

History and mythology

Hercules represents the Greek hero Heracles, named after Hera, the queen of the gods. According to Greek mythology, Heracles was the son of Zeus and a mortal woman named Alcmene. Hera was very upset at Zeus' infidelity, and therefore caused Heracles to kill his own children.

Heracles consulted the oracle at Delphi and was told that in order to atone for this horrible act he had to serve king Euristeus of Mycenae. The king assigned twelve seemingly impossible tasks, or labors, for him to perform. Among these labors Heracles killed the Nemean lion represented by the constellation Leo, as well as the Hydra. During his battle with the Hydra he also killed the little crab represented by the constellation Cancer. When he went to fetch the golden apples kept in a garden on the slopes of Mount Atlas he fought and killed the dragon Ladon represented by the constellation Draco.

The stars ε, ζ, η, and π form an asterism called the Keystone.


Horologium (Hor)

Names

Latin name	Horologium

Genitive form	Horologii

English name	Clock

German name	Pendeluhr

Area

Horologium covers about 249 square degrees.

History and mythology

Horologium is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille originally called this constellation Horologium Oscillitorium after the pendulum clock invented by the Dutch scientist Christiaan Huygens (1629-1695).


Hydra (Hya)

Names

Latin name	Hydra

Genitive form	Hydrae

English name	Hydra

German name	Hydra

Area

Hydra covers about 1,303 square degrees.

Named stars

Alphard	30 Hya	α Hya

History and mythology

Hydra is the largest constellation in the sky, and in the past it was even larger. Like the constellation Argo Navis, it was broken down into smaller constellations. Hydra was broken up into Corvus, Crater, a smaller Hydra, and Sextans.

According to Greek mythology, the oracle at Delphi ordered Heracles to serve king Euristeus of Mycenae to atone for killing his own children in a fit of madness. The king assigned twelve seemingly impossible tasks, or labors, for him to perform. The second was to kill the hideous monster named the Hydra. The second of these tasks was to kill the Hydra, a dog-like monster with nine heads and breath that could kill on contact. Heracles killed the Hydra and during this battle also killed the little crab represented by the constellation Cancer.

In another legend the bird represented by the constellation Corvus was sent with a cup by the god Apollo to fetch water. The bird saw a fig tree and, wishing to eat the fruit, loitered at the tree and waited for the figs to become ripe.

After eating the ripe fruit the bird returned to Apollo with a water snake in his claws and explained that the snake was the reason he had taken so long to fetch the water. Apollo punished the bird for lying by placing it in the sky along with the cup and water snake represented by the constellations Crater and Hydra. The poor bird is doomed to everlasting thirst because the water snake controls the cup and its contents.


Hydrus (Hyi)

Names

Latin name	Hydrus

Genitive form	Hydri

English name	Water Snake

German name	Wasserschlange

Area

Hydrus covers about 243 square degrees.

History and mythology

Hydrus is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the Southern Hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Hydrus is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.


Indus (Ind)

Names

Latin name	Indus

Genitive form	Indi

English name	Indian

German name	Indianer

Area

Indus covers about 294 square degrees.

History and mythology

Indus is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the Southern Hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Indus is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.

Indus does not represent a person from India, but one of the native peoples encountered by European explorers who traveled to the American continents.


Lacerta (Lac)

Names

Latin name	Lacerta

Genitive form	Lacertae

English name	Lizard

German name	Eidechse

Area

Lacerta covers about 201 square degrees.

History and mythology

Lacerta was named by the German astronomer Johannes Hevelius (1611-1687) in his influential star atlas Firmamentum Sobiescianum sive Uranographia, which was completed by his wife and published in 1690, after his death, in Danzig.


Leo (Leo)

Names

Latin name	Leo

Genitive form	Leonis

English name	Lion

German name	Löwe

Area

Leo covers about 947 square degrees.

Named stars

Regulus	32 Leo	α Leo

Denebola	94 Leo	β Leo

Algieba	41 Leo	γ1 Leo

Zosma	68 Leo	δ Leo

Adhafera	36 Leo	ζ Leo

Chertan	70 Leo	θ Leo

Alterf	4 Leo	λ Leo

Raselas	24 Leo	μ Leo

History and mythology

Heracles killed his own children in a fit of madness caused by Hera, the queen of the gods. To atone for this act, the oracle at Delphi ordered Heracles to serve king Euristeus of Mycenae. The king assigned twelve seemingly impossible tasks, or labors, for him to perform. The first was to kill the Nemean lion. Nemea was a sacred valley in the Peloponnesus that was well-known for its red wine. Unfortunately, a huge lion roamed the countryside and killed anyone it encountered. Heracles' first labor was to kill this lion.

The lion's hide was so tough that Heracles could not kill it using his weapons. Eventually he succeeded in strangling the lion to death with his bare hands. The lion's claws were so sharp that Heracles then used them to cut the animal's hide. He wore the cloak he created with the hide to protect himself from the weapons of others.

The stars α, η, γ, ζ, μ, and ε form an asterism called the Sickle.


Leo Minor (LMi)

Names

Latin name	Leo Minor

Genitive form	Leonis Minoris

English name	Little Lion

German name	Kleiner Löwe

Area

Leo Minor covers about 232 square degrees.

History and mythology

Leo Minor was named by the German astronomer Johannes Hevelius (1611-1687) in his influential star atlas Firmamentum Sobiescianum sive Uranographia, which was completed by his wife and published in 1690, after his death, in Danzig.


Lepus (Lep)

Names

Latin name	Lepus

Genitive form	Leporis

English name	Hare

German name	Hase

Area

Lepus covers about 290 square degrees.

Named stars

Arneb	11 Lep	α Lep

Nihal	9 Lep	β Lep

History and mythology

Lepus is one of the animals hunted by Orion near the bank of the river Eridanus.

The ancient Egyptians associated the constellation we call Orion with Osiris, and saw Lepus as the Boat of Osiris.


Libra (Lib)

Names

Latin name	Libra

Genitive form	Librae

English name	Scales

German name	Waage

Area

Libra covers about 538 square degrees.

Named stars

Zubenelgenubi	9 Lib	α2 Lib

Zubenelschemali	27 Lib	β Lib

History and mythology

The ancient Greeks considered this part of the sky to belong to Scorpius, and thought that it represented the scorpion's claws. The constellation Libra was created later during the days of the Roman Empire.


Lupus (Lup)

Names

Latin name	Lupus

Genitive form	Lupi

English name	Wolf

German name	Wolf

Area

Lupus covers about 334 square degrees.

History and mythology

Lupus is said to represent the wolf sacrificed by Chiron, the centaur represented by the constellation Centaurus, on his altar, represented by the constellation Ara.


Lynx (Lyn)

Names

Latin name	Lynx

Genitive form	Lyncis

English name	Lynx

German name	Luchs

Area

Lynx covers aboiut 545 square degrees.

History and mythology

Lynx was named by the German astronomer Johannes Hevelius (1611-1687) in his influential star atlas Firmamentum Sobiescianum sive Uranographia, which was completed by his wife and published in 1690, after his death, in Danzig.

Hevelius created this constellation to fill the gap that existed between Auriga and Ursa Major.


Lyra (Lyr)

Names

Latin name	Lyra

Genitive form	Lyrae

English name	Lyre

German name	Leier

Area

Lyra covers about 287 square degrees.

Named stars

Vega	3 Lyr	α Lyr

Sheliak	10 Lyr	β Lyr

Sulafat	14 Lyr	γ Lyr

History and mythology

Lyra represents a lyre, a stringed musical instrument similar to a harp. In Greek mythology, the lyre was invented by the god Hermes, who gave it as a gift to his half-brother Apollo. Apollo, the god of music, in turn gave it Orpheus, the musician of the Argonauts.

Eurydice, the wife of Orpheus, was killed by a snake and Orpheus traveled to the underworld to try to bring her back. He played his lyre for Hades, the god of the underworld, who agreed to release Eurydice provided that Orpheus did not turn around and look at her during their journey home. Unfortunately, as they were about to emerge in the sunlight, Orpheus looked back at his wife.

Orpheus is later killed by followers of the god Dionysus and his lyre is thrown into a river. Apollo then asked Zeus to place the lyre among the stars.

Vega, Altair in Aquila, and Deneb in Cygnus form an asterism called the Summer Triangle.


Mensa (Men)

Names

Latin name	Mensa

Genitive form	Mensae

English name	Table Mountain

German name	Tafelberg

Area

Mensa covers about 154 square degrees.

History and mythology

Mensa is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille originally called this constellaton Mons Mensa after Table Mountain, located near his observatory in South Africa.


Microscopium (Mic)

Names

Latin name	Microscopium

Genitive form	Microscopii

English name	Microscope

German name	Mikroskop

Area

Microscopium covers about 210 square degrees.

History and mythology

Mensa is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille named this constellation after the microscope invented by Zacharius Janssen.


Monoceros (Mon)

Names

Latin name	Monoceros

Genitive form	Monocerotis

English name	Unicorn

German name	Einhorn

Area

Monoceros covers about 482 square degrees.

History and mythology

Camelopardalis was invented by the Dutch and astronomer and cartographer Petrus Plancius (1552-1622). Plancius invented a number of new constellations, but only Camelopardalis, Columba, and Monoceros are still accepted today.

The German astronomer Jakob Bartsch included Monoceros on his star map published in 1624.


Musca (Mus)

Names

Latin name	Musca

Genitive form	Muscae

English name	Fly

German name	Fliege

Area

Musca covers about 138 square degrees.

History and mythology

Musca is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the Southern Hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Musca is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.

Bayer originally called this constellation Apis, the bee, but the German astronomer Jakob Bartsch renamed it Musca, the fly, on his star map published in 1624.


Norma (Nor)

Names

Latin name	Norma

Genitive form	Normae

English name	Level

German name	Lineal

Area

Norma covers about 165 square degrees.

History and mythology

Norma is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille originally called it Norma et Regula, the carpenter's level and square, but the name has since been shortened to Norma.


Octans (Oct)

Names

Latin name	Octans

Genitive form	Octantis

English name	Octant

German name	Oktant

Area

Octans covers about 291 square degrees.

History and mythology

Octans is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille originally named this constellation Octans Hadleianus to commemorate the invention of the octant, a navigational instrument used to determine the latitude of a ship by measuring the altitude of the North Star above the horizon. The octant was invented in John Hadley in 1730.


Ophiuchus (Oph)

Names

Latin name	Ophiuchus

Genitive form	Ophiuchi

English name	Ophiuchus

German name	Schlangenträger

Area

Ophiuchus covers about 948 square degrees.

Named stars

Rasalhague	55 Oph	α Oph

Cebalrai	60 Oph	β Oph

Yed Prior	1 Oph	δ Oph

Yed Posterior	2 Oph	ε Oph

Sabik	35 Oph	η Oph

History and mythology

Ophiuchus represents the Greek god of medicine Asclepius, known as Aesculapius to the Romans. Serpents were associated with physicians in ancient times, a fact that can still be seen in the modern symbol for medicine, the caduceus.

Asclepius was the son of the god Apollo and Coronis, the daughter of king Phlegyas of the Lapiths. He was raised and educated by the wise centaur Chiron, represented by the constellation Centaurus. Asclepius was the surgeon that accompanied Jason and the Argonauts in their search for the Golden Fleece.

Asclepius was so skilled in this profession that he could bring the dead back to life. When Orion was bitten by a scorpion he attempted to bring him back to life, and this caused the god Hades to complain. Hades was after all the god of the underworld, the realm of the dead, and so he convinced Zeus to strike Asclepius with a lightning bolt and end his life.

Apollo was very angry that Zeus had killed his son, so he in turn killed the Cyclopes, creatures who manufactured lightning bolts for the king of the gods. Zeus then placed Asclepius in the sky as the constellation Ophiuchus, along with the serpent representing his profession.


Orion (Ori)

Names

Latin name	Orion

Genitive form	Orionis

English name	Orion

German name	Orion

Area

Orion covers about 594 square degrees.

Named stars

Betelgeuse	58 Ori	α Ori

Rigel	19 Ori	β Ori

Bellatrix	24 Ori	γ Ori

Mintaka	34 Ori	δ Ori

Alnilam	46 Ori	ε Ori

Alnitak	50 Ori	ζ Ori

Saiph	53 Ori	κ Ori

Meissa	39 Ori	λ Ori

History and mythology

Orion, the son of the god Poseidon and Euryale, the daughter of King Minos of Crete, boasted that he was the greatest hunter in the world. His arrogance angered the goddess Hera, and she sent a scorpion, represented by the constellation Scorpius, to kill him. Orion and the scorpion fought for a long time, and eventually Orion was stung. The physician Asclepius, represented by the constellation Ophiuchus, attempted to bring him back to life, but was unsuccessful.

The goddess of hunting, Artemis, felt sorry for Orion and so placed him and his hunting dogs, represented by the constellations Canis Major and Canis Minor, in the sky. She also placed the animals he hunted near him in the sky. Orion and his dogs now stand next to the river Eridanus and hunt the rabit and the bull represented by the constellations Lepus and Taurus. Scorpius was placed on the other side of the sky so Orion would not be hurt by it again. But, she was afraid that Scorpius might move across the sky and attack Orion. The gods therefore placed a centaur in the sky and told him to point his arrow right at the scorpion. Orion is now safe, because Scorpius dare not move.

The ancient Egyptians associated Orion with Osiris, the god of the afterlife, and believed that the souls of dead kings became stars and inhabited this region of the sky. The southern shaft of the King's Chamber in the great pyramid of Khufu points directly at the meridian position of Alnitak in 2450 BC.

Betelgeuse, Sirius in Canis Major, and Procyon in Canis Minor form an asterism called the Winter Triangle.

The belt of Orion, made up of the stars Mintaka, Alnilam, and Alnitak, is called the Three Marys in Latin America.


Pavo (Pav)

Names

Latin name	Pavo

Genitive form	Pavonis

English name	Peacock

German name	Pfau

Area

Pavo covers about 378 square degrees.

History and mythology

Hydrus is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the Southern Hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Pavo is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.


Pegasus (Peg)

Names

Latin name	Pegasus

Genitive form	Pegasi

English name	Pegasus

German name	Pegasus

Area

Pegasus covers about 1,121 square degrees.

Named stars

Markab	54 Peg	α Peg

Scheat	53 Peg	β Peg

Algenib	88 Peg	γ Peg

Enif	8 Peg	ε Peg

Homam	42 Peg	ζ Peg

Matar	44 Peg	η Peg

Baham	26 Peg	θ Peg

Sadalbari	48 Peg	μ Peg

History and mythology

Pegasus was the son of Neptune, the god of the sea, and Medusa, a creature so hideous that anyone who looked at her was turned to stone. After Perseus beheaded the gorgon Medusa, some of her blood fell into the sea creating the winged horse.


Perseus (Per)

Names

Latin name	Perseus

Genitive form	Persei

English name	Perseus

German name	Perseus

Area

Perseus covers about 615 square degrees.

Named stars

Mirfak	33 Per	α Per

Algol	26 Per	β Per

Menkib	46 Per	ξ Per

Atik	38 Per	ο Per

History and mythology

Perseus is the hero who rescued Princess Andromeda of Ethiopia from the sea monster Cetus.

Queen Cassiopeia boasted that she and her daughter were more beautiful than any of the sea nymphs known as the Nereids. This offended Poseidon, the god of the sea, and as punishment Andromeda was chained to a rock by the seashore to await being devoured by the sea monster represented by the constellation Cetus.

The hero Perseus beheaded Medusa, and used her head as a weapon against the sea monster. Medusa was a gorgon, a creature so hideous that anyone who looked at her was turned to stone. When Cetus saw the head of Medusa he turned to stone and Andromeda was spared. After rescuing Andromeda from the sea monster, Perseus married her and presented the gorgon's head to the goddess Athena.


Phoenix (Phe)

Names

Latin name	Phoenix

Genitive form	Phoenicis

English name	Phoenix

German name	Phönix

Area

Phoenix covers about 469 square degrees.

History and mythology

Phoenix is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the Southern Hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Phoenix is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.

The Phoenix was said to be a beautiful bird that would live for exactly 500 years. The Phoenix would then build a nest that would be set afire by the sun at noon. The fire would kill the bird, but a small worm would emerge from the ashes and would grow into a new Phoenix.


Pictor (Pic)

Names

Latin name	Pictor

Genitive form	Pictoris

English name	Painter

German name	Maler

Area

Pictor covers about 247 square degrees.

History and mythology

Pictor is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille originally called this constellation Equuleus Pictoris, the painter's easel. The name was eventually shortened and the constellation is now thought to represent the painter himself rather than his easel.


Pisces (Psc)

Names

Latin name	Pisces

Genitive form	Piscium

English name	Fishes

German name	Fische

Area

Pisces covers about 889 square degrees.

Named stars

Alrisha	113 Psc	α Psc

History and mythology

The constellation Pisces represents two fish. During the battle in which the younger Olympian gods overthrew the older Titans a monster called Typhon attacked the Olympians. Pan warned the gods and they all turned themselves into animals to hide from the monster. As the god Pan had done, Aphrodite and her son Eros turned themselves into fish and hid in a river to escape the monster.


Piscis Austrinus (PsA)

Names

Latin name	Piscis Austrinus

Genitive form	Piscis Austrini

English name	Southern Fish

German name	Südlicher Fisch

Area

Piscis Austrinus covers about 245 square degrees.

Named stars

Fomalhaut	24 PsA	α PsA

History and mythology

Piscis Austrinus is associated with Atagartis, the ancient Syrian fertility goddess. She fell into a lake near the river Euphrates and was saved by a fish. She thanked the fish by giving it a place among the stars.


Puppis (Pup)

Names

Latin name	Puppis

Genitive form	Puppis

English name	Stern

German name	Hinterdeck

Area

Puppis covers about 673 square degrees.

Named stars

Naos	ζ Pup

History and mythology

Puppis was originally part of a large constellation named Argo Navis. That constellation represented the ship on which Jason and his companions, the Argonauts, made their journey in search of the Golden Fleece.

Argo Navis was split into the three constellations called Carina, Puppis, and Vela by the French astronomer Nicolas Louis de Lacaille (1713-1762) in his star map published in 1763. Argo Navis was eventually split into the four constellations called Carina, Puppis, Pyxis, and Vela when the International Astronomical Union defined the 88 modern constellations in 1930.


Pyxis (Pyx)

Names

Latin name	Pyxis

Genitive form	Pyxidis

English name	Compass

German name	Kompaß

Area

Pyxis covers about 221 square degrees.

History and mythology

Pyxis is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille named this constellation after a ship's magnetic compass.

Pyxis was originally part of a large constellation named Argo Navis. That constellation represented the ship on which Jason and his companions, the Argonauts, made their journey in search of the Golden Fleece.

Argo Navis was split into the three constellations called Carina, Puppis, and Vela by the French astronomer Nicolas Louis de Lacaille (1713-1762) in his star map published in 1763. Argo Navis was eventually split into the four constellations called Carina, Puppis, Pyxis, and Vela when the International Astronomical Union defined the 88 modern constellations in 1930.


Reticulum (Ret)

Names

Latin name	Reticulum

Genitive form	Reticuli

English name	Net

German name	Netz

Area

Reticulum covers aboue 114 square degrees.

History and mythology

Reticulum is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Although Reticulum, which means "net", is near the constellation Argo Navis, which represents a ship, it does not represent a fishing net. Lacaille named the constellation after a reticle, a set of crossed lines seen through the eyepiece of a of an optical instrument like a microscope or telescope. Such lines were etched into the glass of a telescope's eyepiece, and were used to measure the positions of stars.

Lacaille originally named the constellation Reticulum Rhomboidalis and intended it to commemorate the reticle in the eyepiece of the telescope he used in South Africa to measure the positions of the stars in the southern sky.


Sagitta (Sge)

Names

Latin name	Sagitta

Genitive form	Sagittae

English name	Arrow

German name	Pfeil

Area

Sagitta covers about 80 square degrees.

History and mythology

In Greek mythology, Prometheus was the god that stole fire from the gods on Mount Olympus and gave it to humankind. As punishment, Zeus, the king of the gods, chained Prometheus to a rock and sent an eagle to torment him by eating his liver. Every night Prometheus would heal, and every day the eagle would return again to eat his liver.

Heracles rescued Prometheus from this torture by killing the eagle with an arrow. Sagitta represents this arrow.


Sagittarius (Sgr)

Names

Latin name	Sagittarius

Genitive form	Sagittarii

English name	Archer

German name	Schütze

Area

Sagittarius covers about 867 square degrees.

Named stars

Rukbat	α Sgr

Arkab	β1 Sgr

Alnasel	10 Sgr	γ2 Sgr

Kaus Meridionalis	19 Sgr	δ Sgr

Kaus Australis	20 Sgr	ε Sgr

Ascella	38 Sgr	ζ Sgr

Kaus Borealis	22 Sgr	λ Sgr

Nunki	34 Sgr	σ Sgr

History and mythology

Sagittarius represents a centaur, a creature that has the body of a horse, but has the chest, arms, and head of a man. Sagittarius holds a bow and arrow. So, this centaur is perhaps not as good and wise as Chiron, the centaur represented by the constellation Centaurus.

When the hunter and the scorpion that killed him were placed into the sky as the constellations Orion and Scorpius the gods placed Scorpius on the other side of the sky so Orion would not be hurt by it again. But, they were afraid that Scorpius might move across the sky and attack Orion. The gods therefore placed a centaur in the sky and told him to point his arrow right at the scorpion. Orion is now safe, because Scorpius dare not move.


Scorpius (Sco)

Names

Latin name	Scorpius

Genitive form	Scorpii

English name	Scorpion

German name	Skorpion

Area

Scorpius covers about 497 square degrees.

Named stars

Antares	21 Sco	α Sco

Graffias	8 Sco	β1 Sco

Shaula	35 Sco	λ Sco

Lesath	34 Sco	υ Sco

History and mythology

Orion, the son of the god Poseidon and Euryale, the daughter of King Minos of Crete, boasted that he was the greatest hunter in the world. His arrogance angered the goddess Hera, and she sent a scorpion, represented by the constellation Scorpius, to kill him. Orion and the scorpion fought for a long time, and eventually Orion was stung. The physician Asclepius, represented by the constellation Ophiuchus, attempted to bring him back to life, but was unsuccessful.

The goddess of hunting, Artemis, felt sorry for Orion and so placed him and his hunting dogs, represented by the constellations Canis Major and Canis Minor, in the sky. She also placed the animals he hunted near him in the sky. Orion and his dogs now stand next to the river Eridanus and hunt the rabit and the bull represented by the constellations Lepus and Taurus. Scorpius was placed on the other side of the sky so Orion would not be hurt by it again. But, she was afraid that Scorpius might move across the sky and attack Orion. The gods therefore placed a centaur in the sky and told him to point his arrow right at the scorpion. Orion is now safe, because Scorpius dare not move.


Sculptor (Scl)

Names

Latin name	Sculptor

Genitive form	Sculptoris

English name	Sculptor

German name	Bildhauer

Area

Sculptor covers about 475 square degrees.

History and mythology

Sculptor is one of the constellations named by the French astronomer Nicolas Louis de Lacaille (1713-1762), who mapped the stars visible from the Cape of Good Hope from 1751 to 1753. He originally called it L'Atelier du Sculpteur, the sculptor's workshop.

Sculptor is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille originally named the constellation L'Atelier du Sculpteur, the sculptor's workshop, but the name has since been shortened to Sculptor.


Scutum (Sct)

Names

Latin name	Scutum

Genitive form	Scuti

English name	Shield

German name	Schild

Area

Scutum covers about 109 square degrees.

History and mythology

Lacerta was named by the German astronomer Johannes Hevelius (1611-1687) in his influential star atlas Firmamentum Sobiescianum sive Uranographia, which was completed by his wife and published in 1690, after his death, in Danzig.

Hevelius originally called this constellation Scutum Sobieskii, Sobieski's shield, in honor of his major patron, King Johann Sobieski III of Poland. The constellation commemorates Sobieski's defeat of the Turks at Kalenberg in 1683.


Serpens (Ser)

Names

Latin name	Serpens

Genitive form	Serpentis

English name	Serpent

German name	Schlange

Area

Serpens covers about 637 square degrees.

Named stars

Unukalhai	24 Ser	α Ser

Alya	63 Ser	θ1 Ser

History and mythology

Serpens is the only constellation that is split into two parts. One part, named Serpens Caput, represents the head of the serpent and lies to the west of the Ophiuchus. The other part, named Serpens Cauda, represents the tail of the serpent and lies to the east of Ophiuchus.

Ophiuchus represents the Greek god of medicine Asclepius, known as Aesculapius to the Romans. Serpents were associated with physicians in ancient times, a fact that can still be seen in the modern symbol for medicine, the caduceus.


Sextans (Sex)

Names

Latin name	Sextans

Genitive form	Sextantis

English name	Sextant

German name	Sextant

Area

Sextans covers about 314 square degrees.

History and mythology

Sextans was named by the German astronomer Johannes Hevelius (1611-1687) in his influential star atlas Firmamentum Sobiescianum sive Uranographia, which was completed by his wife and published in 1690, after his death, in Danzig.

Sextans is named after the sextant, a navigational device that replaced the octant.


Taurus (Tau)

Names

Latin name	Taurus

Genitive form	Tauri

English name	Bull

German name	Stier

Area

Taurus covers about 797 square degrees.

Named stars

Aldebaran	87 Tau	α Tau

Alnath	112 Tau	β Tau

Hyadum	54 Tau	γ Tau

Ain	74 Tau	ε Tau

Alcyone	25 Tau	η Tau

Celaeno	16 Tau

Electra	17 Tau

Taygeta	19 Tau

Maia	20 Tau

Asterope	21 Tau

Merope	23 Tau

Atlas	27 Tau

Pleione	28 Tau

History and mythology

Taurus represents Zeus, the king of the gods in Greek mythology. Zeus took the form of a bull to charm and kidnap Europa, the daughter of King Agenor of Phoenicia. Zeus took Europa to the island of Crete, where he revealed his true nature and seduced her. Zeus and Europa had a son who eventually became King Minos of Crete.

Taurus is also thought to simply represent one of the animals hunted by Orion.

The V-shaped group of stars, of which Aldebaran is a part, form an asterism called the Hyades. In Greek mythology the Hyades were the daughters of Atlas and Aethra. One day their older brother, Hyad, was killed by a lioness while out hunting. The sisters were overcome with grief, and the gods took pity on them and placed them in the sky among the stars.

The stars named Alcyone, Asterope, Celaeno, Electra, Maia, and Taygeta form a beautiful asterism called the Pleiades. The Pleiades are also known as the Seven Sisters, or as the Seven Little Goats in Latin America.

The Pleiades were the daughters of Atlas and Pleione, and therefore also half-sisters of the Hyades. Electra, Maia, and Taygeta all became the lovers of Zeus. Three other sisters also had immortal lovers. Alcyone and Celaeno both were seduced by Poseidon, the god of the sea, and Asterope was seduced by Ares, the god of war.


Telescopium (Tel)

Names

Latin name	Telescopium

Genitive form	Telescopii

English name	Telescope

German name	Fernrohr

Area

Telescopium covers about 252 square degrees.

History and mythology

Telescopium is one of the fourteen modern constellations invented by the French theologian and astronomer Nicolas Louis de Lacaille (1713-1762). He traveled to South Africa in 1750 and set up a small observatory near Cape Town. Over the next three years he measured and recorded the positions of almost 10,000 stars. Lacaille returned to France in 1754 and presented his map of the stars visible from Cape Town to the French Royal Academy of Sciences. This map of the southern stars, which included his fourteen new constellations, was published in 1756.

Lacaille originally named the constellation Tubus Telescopium and intended it to commemorate the invention of the telescope.


Triangulum (Tri)

Names

Latin name	Triangulum

Genitive form	Trianguli

English name	Triangle

German name	Dreieck

Area

Triangulum covers about 132 square degrees.

History and mythology

Triangulum is a very old constellation; these stars were referred to as a triangle by the ancient Greeks, Romans, and Arabs. The Greeks called this constellation Deltoton after the capital letter Δ, which is resembles. The Romans associated this constellation with the island of Sicily, which is also triangular in shape. The ancient Egyptians saw Triangulum as a symbol of the triangular Nile delta.


Triangulum Australe (TrA)

Names

Latin name	Triangulum Australe

Genitive form	Trianguli Australis

English name	Southern Triangle

German name	Südliches Dreieck

Area

Triangulum Australe covers about 110 square degrees.

History and mythology

Triangulum Australe is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the Southern Hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Triangulum Australe is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.


Tucana (Tuc)

Names

Latin name	Tucana

Genitive form	Tucanae

English name	Toucan

German name	Tukan

Area

Tucana covers about 295 square degrees.

History and mythology

Triangulum Australe is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the southern hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Tucana is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.


Ursa Major (UMa)

Names

Latin name	Ursa Major

Genitive form	Ursae Majoris

English name	Great Bear

German name	Großer Bär

Area

Ursa Major covers about 1,280 square degrees.

Named stars

Dubhe	50 UMa	α UMa

Merak	48 UMa	β UMa

Phecda	64 UMa	γ UMa

Megrez	69 UMa	δ UMa

Alioth	77 UMa	ε UMa

Mizar	79 UMa	ζ UMa

Alkaid	85 UMa	η UMa

Talitha Borealis	9 UMa	ι UMa

Talitha Australis	12 UMa	κ UMa

Tania Borealis	33 UMa	λ UMa

Tania Australis	34 UMa	μ UMa

Alula Borealis	54 UMa	ν UMa

Alula Australis	53 UMa	ξ UMa

Muscida	1 UMa	ο UMa

Alcor	80 UMa

History and mythology

Ursa Major represents Callisto, the daughter of King Lacaon of Arcadia. Callisto liked to hunt and because a favorite of Artemis, the goddess of hunting. She swore a vow of chastity to the goddess, but gave birth to a son named Arcas as a result of being raped by Zeus, the king of the gods. Hera, the wife of Zeus, was very angry and changed Callisto into a bear.

Callisto roamed the woods for fifteen years in the form of a bear. One day she encountered her son, Arcas, who was in the woods hunting. Arcas, not recognizing his mother in the form of a bear, was about to spear the bear, but Zeus prevented this tragedy by placing both mother and son in the sky. Callisto became the constellation Ursa Major and Arcas became the constellation Bootes.

The ancient Egyptians called this constellation Meskhetiu and associated these stars with a khepesh, a foreleg of an ox. The foreleg was a choice cut of meat used as an offering and in the magical rituals called the "opening of the mouth" ceremony performed on the mummy of a deceased person. The foreleg was a symbol of royal and divine strength, and its use during royal burial rituals probably represented a symbolic transfer of power. Ursa Major is always depicted as a foreleg in astronomical paintings until the end of the Middle Kingdom. From the New Kingdom on it is also shown as a bull or even a bull-headed foreleg.

Ursa Major has been seen as representing a bear in many cultures, and as a chariot or wagon in many others. The ancient Chinese thought of it as a charriot that carried the emperor of heaven.

Ursa Major contains a distinctive group of stars known as the Big Dipper. This asterism is known by different names across the world. During the nineteenth century slaves in America's southern states would "follow the Drinking Gourd" by night to guide them to the northern states and to freedom. The Big Dipper is known as the Plough in Great Britain, and as the Wagon in Germany. In France the asterism is sometimes referred to as the Saucepan.


Ursa Minor (UMi)

Names

Latin name	Ursa Minor

Genitive form	Ursae Minoris

English name	Little Bear

German name	Kleiner Bär

Area

Ursa Minor covers about 256 square degrees.

Named stars

Polaris	1 UMi	α UMi

Kochab	7 UMi	β UMi

Pherkad	13 UMi	γ UMi

Yildun	23 UMi	δ UMi

History and mythology

Before being considered a separate constellation, Ursa Minor was thought to form the wings of the dragon represented by the constellation Draco.

The ancient Egyptians associated these stars with the adze of the god Wepwawet, the "opener of the ways". Instruments shaped like this constellation's pattern of stars were used in the "opening of the mouth" ceremony. The king's successor performed this important ceremony on his mummy so the dead king could be resurrected and could ascend into the celestial kingdom of Osiris, associated with the constellation Orion.

The northern shaft of the Queen's Chamber in the Great Pyramid of Khufu at Giza points directly at the upper meridian position of Kochab in 2450 BC.

The constellation Ursa Minor contains a distinctive group of stars known as the Little Dipper. The Little Dipper is not a constellation itself, but is an asterism.


Vela (Vel)

Names

Latin name	Vela

Genitive form	Velorum

English name	Sail

German name	Segel

Area

Vela covers about 500 square degrees.

Named stars

Alsuhail	λ Vel

History and mythology

Vela was originally part of a large constellation named Argo Navis. That constellation represented the ship on which Jason and his companions, the Argonauts, made their journey in search of the Golden Fleece.

Argo Navis was split into the three constellations called Carina, Puppis, and Vela by the French astronomer Nicolas Louis de Lacaille (1713-1762) in his star map published in 1763. Argo Navis was eventually split into the four constellations called Carina, Puppis, Pyxis, and Vela when the International Astronomical Union defined the 88 modern constellations in 1930.


Virgo (Vir)

Names

Latin name	Virgo

Genitive form	Virginis

English name	Maiden

German name	Jungfrau

Area

Virgo covers about 1,294 square degrees.

Named stars

Spica	67 Vir	α Vir

Alaraph	5 Vir	β Vir

Porrima	29 Vir	γ Vir

Vindemiatrix	47 Vir	ε Vir

Zaniah	15 Vir	η Vir

Syrma	99 Vir	ι Vir

History and mythology

Virgo is sometimes thought to represent Persephone, the daughter of Zeus and Demeter, the goddess of fertility. Hades, god of the underworld, abducted Persephone and took her to the underworld to become his wife. Demeter searched for her missing daughter, and when she found out what had happened to her, she asked Hades to release her. Zeus intervened and ordered that Persephone spend half a year with her mother and half a year with Hades in the underworld.

This constellation is also said to represent Dike, the Greek goddess of justice. The neighboring constellation Libra is said to represent the scales of justice.

Virgo is also associated with Erigone, the daughter of Icarius. In Greek mythology Icarius was a mortal who had received the secret of wine making from the god Dionysus. One day a group of peasants blamed Icarius for giving them the wine that they thought had poisoned them. These peasants killed Icarius, and Erigone was guided to her father's body by Maera, his little dog. Erigone was so upset at her father's murder that she killed herself. The gods took pity on the family and placed Icarius in the sky as the constellation Bootes; Erigone became the constellation Virgo, and the Maera became the constellation Canis Minor.


Volans (Vol)

Names

Latin name	Volans

Genitive form	Volantis

English name	Flying Fish

German name	Fliegender Fisch

Area

Volans covers about 141 square degrees.

History and mythology

Volans is one of twelve modern constellations invented by two Dutch navigators, Pieter Dirkszoon Keyser and Frederick de Houtman. The Dutch astronomer and cartographer Petrus Plancius (1552-1622) asked Keyser to chart the stars visible from the Southern Hemisphere during his first voyage to the East Indies in 1595. Frederick de Houtman assisted Keyser, who died in Java in 1596, during the first voyage and refined their star charts on subsequent voyages.

Volans is one of twelve new constellations introduced by Johann Bayer in the first true star atlas, his influential work Uranometria, published in 1603. Bayer's work was the first map of the sky to cover the entire celestial sphere. Bayer had not seen the entire sky, only the parts visible to him in Europe. He based parts of his star atlas on the sketches of the southern stars brought back by Keyser and de Houtman.

Bayer originally called this constellation Piscis Volans, the flying fish, but the name has since been shortened to Volans.


Vulpecula (Vul)

Names

Latin name	Vulpecula

Genitive form	Vulpeculae

English name	Fox

German name	Fuchs

Area

Vulpecula covers about 268 square degrees.

History and mythology

Vulpecula was named by the German astronomer Johannes Hevelius (1611-1687) in his influential star atlas Firmamentum Sobiescianum sive Uranographia, which was completed by his wife and published in 1690, after his death, in Danzig.

He originally named the constellation Vulpecula cum Anser, the little fox with the goose. Hevelius was probably inspired to name the constellation this by a song well known to German children,

Fuchs, du hast die Gans gestohlen,

Gib sie wieder her.

Sonst wird dich der Jäger holen,

mit dem Schießgewehr.

which means

Fox, you stole the goose,

Give her back.

Otherwise the hunter will get you,

With his rifle.


Data bar

The Data bar is initially displayed along the right side of the sky chart, above the Pointer bar. The panes in the Data bar display the local and universal time and other information about the sky chart. Click a pane to access a dialog box or perform a related command. For example, click the pane that displays the local time to display the Local Time dialog box.

Use the Data Bar command on the View menu to display or hide the Data bar.

To turn a docked bar into a floating bar, move the pointer over the empty area around the bar's buttons, press and hold down the mouse button, and then drag the pointer away, toward the center of the sky chart. When the bar's outline has changed shape and is where you want it, release the mouse button.

To turn a floating bar into a docked bar, move the pointer over the bar's title bar, press and hold down the mouse button, and then drag the pointer to any edge of the sky chart. When the bar's outline has changed shape and is where you want it, release the mouse button.


Local time pane (Data bar)

This pane displays the local time.

Click this pane to quickly access the Local Time dialog box.


Universal time pane (Data bar)

This pane displays the universal time.

Click this pane to quickly access the Universal Time dialog box.


Julian date pane (Data bar)

This pane displays the Julian date.

Click this pane to quickly access the Julian Date dialog box.


Local sidereal time pane (Data bar)

This pane displays the local sidereal time.

Click this pane to quickly access the Location dialog box.


Zoom level pane (Data bar)

This pane displays the current zoom level and field of view.

Click this pane to quickly access the Zoom Level dialog box.


Limiting magnitude of stars pane (Data bar)

This pane (on the left) displays the limiting magnitude of stars.

Click this pane to quickly access the Stars dialog box.


Limiting magnitude of deep sky objects pane (Data bar)

This pane (on the right) displays the limiting magnitude of deep sky objects.

Click this pane to quickly access the Deep Sky Objects dialog box.


Lunar illumination pane (Data bar)

This pane displays the illumination of the lunar disk.

Click this pane to quickly access the Lunar Phases Data dialog box.


The brightest stars

The following table lists the apparent magnitudes (m), absolute magnitudes (M), and distances (in light years) of the 25 brightest stars in the sky, not counting the sun:

No.	Star	m	M	Distance

 1	α CMa	Sirius	-1.46	 1.4	   8.6

 2	α Car	Canopus	-0.72	-2.5	  74

 3	α Cen	Rigelkent	-0.27	 4.4	   4.3

 4	α Boo	Arcturus	-0.04	 0.2	  34

 5	α Lyr	Vega	 0.03	 0.6	  25

 6	α Aur	Capella	 0.08	 0.4	  41

 7	β Ori	Rigel	 0.12	-8.1	1400

 8	α CMi	Procyon	 0.38	 2.6	  11.4

 9	α Eri	Achernar	 0.46	-1.3	  69

10	α Ori	Betelgeuse	 0.50	-7.2	1400

11	β Cen	Hadar	 0.61	-4.4	 320

12	α Cru	Acrux	 0.76	-4.6	 510

13	α Aql	Altair	 0.77	 2.3	  16

14	α Tau	Aldebaran	 0.85	-0.3	  60

15	α Sco	Antares	 0.96	-5.2	 520

16	α Vir	Spica	 0.98	-3.2	 220

17	β Gem	Pollux	 1.14	 0.7	  40

18	α PsA	Fomalhaut	 1.16	 2.0	  22

19	β Cru	Becrux	 1.25	-4.7	 460

20	α Cyg	Deneb	 1.25	-7.2	1500

21	α Leo	Regulus	 1.35	-0.3	  69

22	ε CMa	Adhara	 1.50	-4.8	 570

23	α Gem	Castor	 1.57	 0.5	  49

24	γ Cru	Gacrux	 1.63	-1.2	 120

25	λ Sco	Shaula	 1.63	-3.5	 330


The nearest stars

The following table lists the apparent magnitudes (m) and distances (in light years) of the 25 nearest stars, not counting the sun:

No.	Star	m	Distance

 1	Proxima Centauri	11.22	 4.22

 2	α Centauri A	-0.01	 4.40

 3	α Centauri B	 1.33	 4.40

 4	Barnard's Star	 9.54	 5.94

 5	Wolf 359	13.46	 7.78

 6	BD+362147	 7.48	 8.31

 7	Sirius A	-1.46	 8.60

 8	Sirius B	 8.44	 8.60

 9	L726-8A	12.56	 8.73

10	L726-8B	12.96	 8.73

11	Ross 154	10.45	 9.69

12	Ross 248	12.27	10.32

13	ε Eridani	 3.73	10.50

14	CD-3615693	 7.34	10.73

15	Ross 128	11.11	10.89

16	L789-6A	12.32	11.27

17	L789-6B	12.50	11.27

18	61 Cygni A	 5.21	11.36

19	Procyon A	 0.38	11.41

20	Procyon B	10.70	11.41

21	61 Cygni B	 6.03	11.43

22	BD+591915B	 9.69	11.47

23	BD+591915A	 8.91	11.64

24	BD+4344A	 8.07	11.64

25	BD+4344B	11.10	11.64


The Greek alphabet

The lowercase letters of the Greek alphabet are used in the system of stellar nomenclature devised by Johann Bayer in 1603. The brightest star in a given constellation is generally designed α, the second brightest β, the third brightest γ, and so on. The following table lists the complete Greek alphabet:

No.	Letter	Name

 1	Α, α	alpha

 2	Β, β	beta

 3	Γ, γ	gamma

 4	Δ, δ	delta

 5	Ε, ε	epsilon

 6	Ζ, ζ	zeta

 7	Η, η	eta

 8	Θ, θ	theta

 9	Ι, ι	iota

10	Κ, κ	kappa

11	Λ, λ	lambda

12	Μ, μ	mu

13	Ν, ν	nu

14	Ξ, ξ	xi

15	Ο, ο	omicron

16	Π, π	pi

17	Ρ, ρ	rho

18	Σ, σ	sigma

19	Τ, τ	tau

20	Υ, υ	upsilon

21	Φ, φ	phi

22	Χ, χ	chi

23	Ψ, ψ	psi

24	Ω, ω	omega


The magnitude scale

The Greek astronomer Hipparchus introduced the magnitude scale when he produced the first well-known star catalog in 129 BC. To indicate the brightness of each star included in his catalog, he ranked them in six classes of magnitude. The brightest stars were assigned to the first magnitude and the faintest stars were assigned to the sixth magnitude.

Although the magnitude scale was useful, it was not possible to answer the question "how much brighter is a second magnitude star than a fourth magnitude star or a sixth magnitude star?" because the scale was not precisely defined. This presented a problem after the invention of the telescope, when astronomers saw stars fainter than those of the sixth magnitude. Astronomers therefore expanded the magnitude scale to include these fainter stars, and to make it possible to assign magnitudes to objects that are brighter than stars. The following table lists the apparent magnitudes (m) of various objects on the modern magnitude scale:

Object	m

Sun	-26.7

Full moon	-12.5

Venus at brightest	 -4.4

Mars and Jupiter at brightest	 -2.8

Sirius	 -1.5

Arcturus, Capella, Vega	  0.0

Saturn at brightest	  0.2

Aldebaran, Antares, Betelgeuse	  1.0

Polaris	  2.0

Uranus	  5.6

Naked-eye limit	  6.0

Neptune	  8.2

Pluto	 13.7

In 1856 the English astronomer Norman R Pogson proposed that a difference of five magnitudes correspond exactly to a brightness ratio of 100 to 1. The brightness ratio of two stars that differ by one magnitude is therefore equal to the fifth-root of 100, or 2.512, a quantity known as the Pogson ratio. The following table lists the brightness ratios for a range of magnitude differences:

Difference	Ratio

0	    1.00

0.1	    1.10

0.2	    1.20

0.3	    1.32

0.4	    1.45

0.5	    1.58

0.6	    1.74

0.7	    1.91

0.8	    2.09

0.9	    2.29

1	    2.51

1.5	    3.98

2	    6.31

2.5	   10.0

3	   15.9

3.5	   25.1

4	   39.8

4.5	   63.1

5	  100

6	  251

7	  631

7.5	1,000

Using this table we can answer the question posed above: a second magnitude star is exactly 6.31 times brighter than a fourth magnitude star, and 39.8 times brighter than a sixth magnitude star.


Spectral types

Stars are classified into types based on the presence, absence, and relative strengths of absorption and emission lines in their light. These spectral features are dependent on the temperatures in the outer layer of a star and the spectral sequence therefore orders stars by their temperatures.

This classification scheme was developed by Annie Jump Cannon (1863-1941) and her colleagues at Harvard Observatory and was internationally adopted in 1910.

The list below describes each of the spectral types. Color specifies the default color used by CyberSky to display stars of this spectral type. Percentage specifies the percentage of stars that belong to this spectral type. As you can see, most stars are of spectral type M.

O

Temperature	25,000 - 50,000 K

24,700 - 49,700 C

44,500 - 89,500 F

Color	Violet

Percentage of stars	0.1

Examples	Mintaka (δ Orionis)

Alnitak (ζ Orionis)

B

Temperature	11,000 - 25,000 K

10,700 - 24,700 C

19,300 - 44,500 F

Color	Cyan

Percentage of stars	0.1

Examples	Rigel (β Orionis)

Regulus (α Leonis)

A

Temperature	7,500 - 11,000 K

7,230 - 10,700 C

13,000 - 19,300 F

Color	White

Percentage of stars	1

Examples	Vega (α Lyrae)

Sirius (α Canis Majoris)

F

Temperature	6,000 - 7,500 K

5,730 - 7,230 C

10,300 - 13,000 F

Color	Yellow

Percentage of stars	2

Examples	Procyon (α Canis Minoris)

Polaris (α Ursae Minoris)

G

Temperature	5,000 - 6,000 K

4,730 - 5,730 C

8,540 - 10,300 F

Color	Orange

Percentage of stars	4

Examples	Sun

Capella (α Aurigae)

K

Temperature	3,500 - 5,000 K

3,230 - 4,730 C

5,840 - 8,540 F

Color	Orange

Percentage of stars	14

Examples	Arcturus (α Bootis)

Aldebaran (α Tauri)

M

Temperature	2,000 - 3,500 K

1,730 - 3,230 C

3,140 - 5,840 F

Color	Coral

Percentage of stars	72

Examples	Betelgeuse (α Orionis)

Antares (α Scorpii)


Luminosity classes

Luminosity classes are categories, indicated by Roman numerals, used to express the size of stars. Small stars have dense atmospheres that exhibit high gas pressures, whereas large stars have immense, extended atmospheres that exhibit low gas pressures.

The characteristics of absorption lines and bands in the spectra of stars are highly dependent on atmospheric pressure, and therefore are an indication of a star's size. These characteristics are studied to determine the luminosity class of a given star.

William W Morgan and Philip C Keenan introduced what is now known as the M-K luminosity classification scheme in 1937.

Class	Description

Ia	Bright supergiants

Ib	Supergiants

II	Bright giants

III	Giants

IV	Subgiants

V	Dwarfs

VI	Subdwarfs

VII	White dwarfs

Stars within each group can be further differentiated by the addition of suffixes such as "a", "ab", and "b". In addition, a star that cannot be classified with certainty may be assigned a hyphenated classification such as "IIIa-IIIb".


Measuring the distances of stars

Over the course of half a year, as the earth moves from one side of its orbit to the other side, the apparent positions of nearby stars shift slightly in relation to stars that are much farther away. The size of the shift in a star's position, known as its parallax, can be used to calculate the distance of the star. The diagram below illustrates the geometry responsible for this effect.

To understand this effect, hold your thumb at arm's length in front of your face, and then look at your thumb first with one eye, and then with the other. As you switch from one eye to the other you'll see your thumb's position shift in relation to objects that are farther away. Because you're eyes are separated by a small distance, when you switch from one eye to the other you're actually seeing your thumb from a slightly different direction. Repeat this experiment, but hold you thumb closer to your face. You'll see that the shift in your thumb's position will be larger than it was before.

This effect allows us to measure the distances of nearby stars. The position of a star is measured very precisely and this measurement is repeated half a year later when the earth has moved to the other side of its orbit. The star's parallax, p, is equal to half its shift in position, and is usually measured in arc seconds. Once this value is known the star's distance in parsecs, D, can be calculated using the formula D = 1 / p. For example, if a star's parallax is measured to be 0.5 arc seconds, then we know its distance is 2 parsecs, or about 6.5 light years.

Observatories on the earth's surface can measure parallax angles as small as 0.01 arc seconds, allowing the distances of stars as far as 100 parsecs away to be measured. If you consider that our galaxy is about 30,000 parsecs across, you'll realize that the parallax method can only be used on a small fraction of stars. The Hipparchos spacecraft has improved this situation somewhat. It can measure parallax angles as small as 0.002 arc seconds, which allows the distances of stars as far as 500 light years away to be determined.


Solar and sidereal time

The diagram below helps explain the difference between solar time and sidereal time. Simply put, solar time is time measured with respect to the sun, and sidereal time is time measured with respect to the stars.

When the earth is at point A, the sun and a distant star appear to lie in the same direction. As the earth moves along its orbit from point A to point B, it rotates exactly once with respect to the star. When the earth is at point B the star has returned to the same position it had at point A. It takes the earth about 23 hours and 56 minutes to move from point A to point B, and to rotate once with respect to the star. This period is called a sidereal day.

At this point the earth has moved along its orbit by approximately one degree, so the sun is no longer located directly in front of the star. As the earth moves from point B to point C it also rotates another degree, which brings the sun back to the same position it had at point A. It takes the earth 24 hours to move from point A to point C, and to rotate once with respect to the sun. This period is called a solar day.


Planetary configurations

The diagram below illustrates the terminology used to describe a planet's position with respect to the earth and the sun.

The smallest circle represents the orbit of an inferior planet such as Mercury or Venus. The middle circle represents the orbit of the earth. The largest circle represents the orbit of a superior planet such as Mars, Jupiter, Saturn, Uranus, Neptune, or Pluto.


Retrograde motion

The diagram below illustrates the reason for the retrograde motion of a superior planet seen from the earth.

Planets that are closer to the sun move more quickly than planets that are farther away. The earth therefore moves more quickly along its orbit than does a superior planet, and at some point the earth will catch up to and move past the planet. This happens when the planet is near opposition, that is, when the planet and the sun are on opposite sides of the earth. The result is that the superior planet slows down and eventually turns around. The planet appears to move backward for a while before slowing down again and eventually moving forward again.

To understand this, imagine driving down a highway in a car and passing a slower car in another lane. Even though the other car is moving forward, it will appear to be moving backward in relation your car and the scenery outside. Similarly, when the earth overtakes and moves past a superior planet, the planet appears to move backward with respect to the background stars.

The inferior planets, which move faster in their orbits than the earth, exhibit retrograde motion after they pass greatest eastern elongation and near inferior conjunction.


Meteor showers

Meteoroids are small bodies, about the size of a grain of sand, that travel around the sun. When one enters the earth's atmosphere, it moves with such a high velocity that the air becomes luminously hot, resulting in a streak of light known as a meteor. On any given night it's possible to see half a dozen meteors shooting randomly across the sky, provided the sky is clear and dark.

At certain times of the year the number of meteors that can be seen increases dramatically. This is because comets leave trails of meteoroids behind as they travel around the sun. The earth's orbit crosses some of these trails, resulting in annual meteor showers. Because the meteoroids associated with a given shower travel through space along similar orbits, the meteors they produce appear to originate from the same point of the sky. This point is known as the shower's radiant.

Quadrantids

Period	January 1 to January 5

Maximum	January 4

Radiant	15h 28m +50°

Rate	100

April Lyrids

Period	April 19 to April 24

Maximum	April 22

Radiant	18h 08m +32°

Rate	15

η-Aquarids

Period	May 1 to May 8

Maximum	May 5

Radiant	22h 24m -02°

Rate	20

June Lyrids

Period	June 10 to June 21

Maximum	June 16

Radiant	18h 32m +35°

Rate	10

Ophiuchids

Period	June 17 to June 26

Maximum	June 20

Radiant	17h 20m -20°

Rate	15

Capricornids

Period	July 10 to August 5

Maximum	July 25

Radiant	21h 00m -15°

Rate	15

δ-Aquarids

Period	July 15 to August 15

Maximum	July 29

Radiant	22h 36m -17°

Rate	35

Pisces Australids

Period	July 15 to August 20

Maximum	July 30

Radiant	22h 40m -30°

Rate	15

α-Capricornids

Period	July 15 to August 25

Maximum	August 1

Radiant	20h 36m -10°

Rate	10

ι-Aquarids

Period	July 15 to August 25

Maximum	August 5

Radiant	22h 32m -15°

Rate	15

Perseids

Period	July 25 to August 18

Maximum	August 12

Radiant	03h 04m +58°

Rate	70

κ-Cygnids

Period	August 18 to August 22

Maximum	August 20

Radiant	19h 20m +55°

Rate	10

Orionids

Period	October 16 to October 27

Maximum	October 21

Radiant	06h 24m +15°

Rate	35

Taurids

Period	October 10 to December 5

Maximum	November 1

Radiant	03h 28m +14°

Rate	15

Leonids

Period	November 14 to November 20

Maximum	November 17

Radiant	10h 08m +22°

Rate	20 (500,000 in 1966!)

Geminids

Period	December 7 to December 15

Maximum	December 13

Radiant	07h 28m +32°

Rate	55

Ursids

Period	December 17 to December 24

Maximum	December 22

Radiant	14h 28m +78°

Rate	20

The coordinates of a shower's radiant, given in right ascension and declination, specify the point from which a shower's meteors will appear to be originating. The rate of a shower's meteors is variable, and can be much higher if the shower's parent comet has recently crossed the earth's orbit.


Temperature scales

The Kelvin scale was invented in 1848 by British physicist William Thomson (1824-1907), also known as Lord Kelvin. This scale is used in all scientific work. The Celsius scale was invented in 1742 by Swedish astronomer Anders Celsius (1701-1744) and is used throughout most of the world. The Fahrenheit scale was invented in 1709 by the German physicist Gabriel Daniel Fahrenheit (1686-1736) and is used in the United States. The following table compares these three temperature scales:

Kelvin	Celsius	Fahrenheit

 373	 100	 212	Boiling point of water

 273	   0	  32	Freezing point of water

   0	-273	-460	Absolute zero

Use the following steps to convert temperatures from one scale to another:

To convert	Do this

Kelvin to Celsius	Subtract 273

Fahrenheit to Celsius	Subtract 32, divide by 1.8

Celsius to Fahrenheit	Multiply by 1.8, add 32


Units of distance

The following table compares various units of distance:

This unit	Equals

1 inch	2.54 centimeters

1 foot	12 inches

30.48 centimeters

1 yard	3 feet

91.44 centimeters

1 meter	39.37 inches

3.281 feet

1.0936 yards

1 kilometer	0.6215 miles

1 mile	1.609 kilometers

1 astronomical unit	149,597,870 kilometers

92,955,807 miles

1 light year	9,460,000,000,000 kilometers

5,880,000,000,000 miles

63,240 astronomical units

0.307 parsecs

1 parsec	30,900,000,000,000 kilometers

19,200,000,000,000 miles

3.26 light years

206,265 astronomical units


About CyberSky dialog box

Use the About CyberSky dialog box to view the name, version number, and copyright notice for your copy of CyberSky, as well as information on how to contact the program's author.

Display the About CyberSky dialog box by using the About CyberSky command on the Help menu.

OK

Click this button to close this dialog box.


Bitmap Setup dialog box

Use the Bitmap Setup dialog box to specify the dimensions of the sky chart you'd like to save as a bitmap.

Display the Bitmap Setup dialog box by using the Save Bitmap command on the File menu, or by pressing the Ctrl+B keys.

If you are running Windows in 8-bit color mode, an 8-bit (256 color) bitmap will be created. If you are running in 15-, 16-, 24-, or 32-bit color mode, a 24-bit (True Color) bitmap will be created.

640 X 480, 800 X 600, 1024 X 768, 1152 X 864, 1280 X 1024, 1600 X 1200

Click one of these buttons to set the dimensions of the bitmap to a standard desktop size. Perfect for Windows wallpaper!

Width, Height

Enter the dimensions of the bitmap into these boxes, or use the spin buttons to modify the displayed values.

OK

Click this button to close this dialog box and save a bitmap. The Save As dialog box will be displayed to allow you to specify the name of the bitmap.

Cancel

Click this button to close this dialog box without saving a bitmap.

Help

Click this button to display Help for this dialog box.


Color Browser dialog box

Use the Color Browser dialog box to preview and select a color used to display an item on the screen or on a printer.

Display the Color Browser dialog box by clicking the Edit button in the Colors dialog box.

Colors

Select one of the colors displayed in this box.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Colors dialog box

Use the Colors dialog box to customize the colors used to display items on the screen or on a printer.

Display the Colors dialog box by using the Colors command on the Options menu.

Color

Select the Screen or Printer option to specify whether you want to change a screen or printer color.

Sample

Shows the color used to display the selected item.

Item

Select an item to edit or reset.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Edit

Click this button to edit the color of the selected item.

Reset

Click this button to reset the color of the selected item.

Reset All

Click this button to reset the colors of all the items in the list.

Help

Click this button to display Help for this dialog box.


Constellations dialog box

Use the Constellations dialog box to set constellation display options.

Display the Constellations dialog box by using the Constellations command on the Chart menu.

Figures

Check this box to display constellation figures. These figures are not sanctioned by any official body, and the ones displayed by CyberSky may differ significantly from those you see displayed in books and magazines. Different authors use different sets of figures, some perhaps more attractive and suggestive of the objects after which the constellations are named than others.

Zodiacal only

Check this box to display only zodiacal constellation figures.

Boundaries

Check this box to display constellation boundaries. Constellation boundaries are official, having been established to define the 88 modern constellations by the International Astronomical Union in 1930.

Labels

Check this box to display constellation labels.

Label type

Select the type of label you'd like to see.

Abbreviations such as "Aql" and "Ari". These abbreviations are the official abbreviations designated by the International Astronomical Union.

Latin names such as "Aquila" and "Aries". These names are the official names of the constellations designated by the International Astronomical Union.

English names such as "Eagle" and "Ram". These names are simply English translations of the Latin names, and are not official.

German names such as "Adler" and "Widder". These names are simply German translations of the Latin names, and are not official.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Deep Sky Objects dialog box

Use the Deep Sky Objects dialog box to set deep sky object display options. The registered version of CyberSky includes 472 deep sky objects to magnitude 8.5, but the shareware version includes only 68 deep sky objects to magnitude 5.0.

Display the Deep Sky Objects dialog box by using the Deep Sky Objects command on the Chart menu, or by clicking the Data bar pane that displays the limiting magnitude for deep sky objects.

Deep sky objects include galaxies outside our own galaxy, globular clusters that surround our galaxy, and nebulae and open clusters found within our galaxy. CyberSky displays deep sky objects using the symbols traditionally employed in star atlases. Whenever possible, the symbols are displayed in sizes that reflect the true sizes of the associated deep sky objects.

Deep sky objects

Check this box to display deep sky objects.

Labels

Check this box to display deep sky object labels.

Label type

Select the type of label you'd like to see.

Popular names such as "Lagoon Nebula" and "Jewel Box Cluster". If a deep sky object does not have a popular name, no label will be displayed.

Catalog numbers such as "M 8" and "NGC 4755". A given deep sky object will be labeled with the most common catalog number used to refer to it.

Automatic

Check this box to have CyberSky automatically adjust the limiting magnitude for you. The limiting magnitude will increase when you zoom in, and will decrease when you zoom out.

Magnitude

Move the slider left to include fewer deep sky objects in the sky chart, or right to include more deep sky objects.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Deep Sky Object Data dialog box

Use the Deep Sky Object Data dialog box to display information about a deep sky object. This information includes the object's name, up to two catalog numbers, equatorial and horizontal coordinates, magnitude, the constellation it is in, its rising, transit, and setting times, and its type. The equatorial and horizontal coordinates are apparent topocentric coordinates.

Display this dialog box by clicking on a deep sky object with the right mouse button and then selecting the corresponding About command on the popup menu that appears.

OK

Click this button to close this dialog box.

Copy

Click this button to copy the data displayed in this dialog box onto the clipboard. After the data has been copied onto the clipboard, it can be pasted into an editor or word processor, and then saved to a file or printed. To align the data in an editor or word processor, specify a fixed-width font such as Courier New.

Help

Click this button to display Help for this dialog box.


Equatorial Coordinates dialog box

Use the Equatorial Coordinates dialog box to specify a set of equatorial coordinates, right ascension and declination, that you'd like to search for.

Display the Equatorial Coordinates dialog box by using the Equatorial Coordinates command on the Search menu.

Right ascension

Specify the right ascension.

Declination

Specify the declination.

OK

Click this button to close this dialog box and search for the coordinates.

Cancel

Click this button to close this dialog box without searching for the coordinates.

Help

Click this button to display Help for this dialog box.


Event dialog box

Use the Event dialog box to view the sun, the moon, or a planet when it rises, transits, or sets. The local time will be set to that of the event you're interested in, and the object you select will be centered.

Display the Event dialog box by using the Event command on the Time menu, or by pressing the Ctrl+E keys.

Object

Select one of the solar system objects in this box.

Event

Select one of the events in this box.

OK

Click this button to close this dialog box and update the sky chart.

Cancel

Click this button to close this dialog box without updating the sky chart.

Help

Click this button to display Help for this dialog box.


Fonts dialog box

Use the Fonts dialog box to customize the fonts used to display items on the screen and on a printer.

Display the Fonts dialog box by using the Fonts command on the Options menu.

Font

Select the Screen or Printer option to specify whether you want to change a screen or printer font.

Sample

Shows the font used to display the selected item.

Item

Select an item to edit or reset.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Edit

Click this button to edit the font of the selected item.

Reset

Click this button to reset the font of the selected item.

Reset All

Click this button to reset the fonts of all the items in the list.

Help

Click this button to display Help for this dialog box.


Grids dialog box

Use the Grids dialog box to display or hide coordinate system grids and grid labels.

Display the Grids dialog box by using the Grids command on the Chart menu.

Equatorial grid

Check this box to display the equatorial coordinate system grid.

Horizontal grid

Check this box to display the horizontal coordinate system grid.

Labels

Check this box to display grid labels.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Horizontal Coordinates dialog box

Use the Horizontal Coordinates dialog box to specify a set of horizontal coordinates, azimuth and altitude, that you'd like to search for.

Display the Horizontal Coordinates dialog box by using the Horizontal Coordinates command on the Search menu.

Azimuth

Specify the azimuth.

Altitude

Specify the altitude.

OK

Click this button to close this dialog box and search for the coordinates.

Cancel

Click this button to close this dialog box without searching for the coordinates.

Help

Click this button to display Help for this dialog box.


Julian Date dialog box

Use the Julian Date dialog box to change the time by entering a Julian date.

Display the Julian Date dialog box by using the Julian Date command on the Time menu, or by pressing the Ctrl+J keys.

Julian date

To specify a Julian date, enter a number into the Julian date box or click the spin buttons to change the displayed Julian date. CyberSky's limits of 4000 BC to 4000 AD correspond to Julian dates 260423.5 and 3182029.5, respectively.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Lines dialog box

Use the Lines dialog box to display or hide reference lines.

Display the Lines dialog box by using the Lines command on the Chart menu.

Ecliptic

Check this box to display the ecliptic. When the ecliptic is displayed, a cross labeled "NEP" marks the position of the north ecliptic pole, and another one labeled "SEP" marks the position of the south ecliptic pole.

Celestial equator

Check this box to display the celestial equator. When the celestial equator is displayed, a cross labeled "NCP" marks the position of the north celestial pole, and another one labeled "SCP" marks the position of the south celestial pole.

Galactic equator

Check this box to display the galactic equator. When the galactic equator is displayed, a cross labeled "NGP" marks the position of the north galactic pole, and another one labeled "SGP" marks the position of the south galactic pole.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Local Time dialog box

Use the Local Time dialog box to change the local date and time, and to specify whether daylight saving time is in effect.

Display the Local Time dialog box by using the Local Time command on the Time menu, by clicking the [image] button on the Animation toolbar, by clicking the Data bar pane that displays the local time, or by pressing the Ctrl+L keys.

Date

To specify the local date, enter month, day, and year numbers into the three boxes or click the spin buttons to change the displayed date. Years must fall in the range 4000 BC to 4000 AD. October 4, 1582 and earlier dates are on the Julian calendar. October 15, 1582 and later dates are on the Gregorian calendar.

The format in which dates are entered and displayed is based on the format specified in the Windows Control Panel under Regional Settings, Date.

Month/day/year format

Day/month/year format

Year/month/day format

Time

To specify the local time, enter hours, minutes, and seconds into the three boxes or click the spin buttons to change the displayed time.

The format in which times are entered and displayed is based on the format specified in the Windows Control Panel under Regional Settings, Time.

12-hour format

24-hour format

Daylight saving time

Check this box to specify that daylight saving time is in effect.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Location dialog box

Use the Location dialog box to specify the location on the earth from which you want to view the sky.

Display the Location dialog box by using the Location command on the Options menu.

Name

To specify the location on the earth from which you want to view the sky, click the down arrow, and then click the name of the location.

Location name containing text

To specify the text to search for, enter it in the box. CyberSky ignores case when searching the location database.

Find Next

Click this button to search for the next location containing the text in the box to the left.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Edit

Click this button to edit the longitude, latitude, and time zone for the location selected in the Name list to the left.

Add

Click this button to add a location to the location database.

Delete

Click this button to delete a location from the location database. Use this option with caution! Once you've deleted a location, the only way to restore it is to reinstall CyberSky.

Set As Home

Click this button to make the location your home location. This will allow you to change the location in the future, as many times as you like, and then quickly return to your home location by using the Return Home command on the Options menu.

Help

Click this button to display Help for this dialog box.


Location Data dialog box

Use the Location Data dialog box to view or edit the longitude, latitude, and time zone settings associated with a location in the location database.

Display the Location Data dialog box by clicking the Edit or Add button in the Location dialog box.

Name

To specify the name of the location, enter a name up to 36 characters in length.

Longitude

To specify the longitude of the location, enter a longitude in degrees, minutes, and seconds, then select "E" to specify an east longitude or "W" to specify a west longitude.

Latitude

To specify the latitude of the location, enter a latitude in degrees, minutes, and seconds, then select "N" to specify a north latitude or "S" to specify a south latitude.

Time zone

To specify the time zone of the location, enter a time in hours and minutes, then select "ahead of UT" to specify a time zone ahead of universal time or "behind UT" to specify a time zone behind universal time.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Lunar Phases Data dialog box

Use the Lunar Phases Data dialog box to display the local times and Julian dates corresponding to the beginning of new moon, first quarter, full moon, and last quarter.

Display the Lunar Phases Data dialog box by using the Lunar Phases command on the Data menu.

Lunar month

Click the Back button to display the local times and Julian dates for the previous lunar month, or the Next button to display the local times and Julian dates for the next lunar month.

OK

Click this button to close this dialog box.

Copy

Click this button to copy the data displayed in this dialog box onto the clipboard. After the data has been copied onto the clipboard, it can be pasted into an editor or word processor, and then saved to a file or printed. To align the data in an editor or word processor, specify a fixed-width font such as Courier New.

Help

Click this button to display Help for this dialog box.


Moon Data dialog box

Use the Moon Data dialog box to display information about the moon. This information includes the moon's equatorial, horizontal, and ecliptic coordinates, distance from the earth, angular diameter, magnitude, the constellation it is in, its rising, transit, and setting times, and the illumination of its disk. The equatorial and horizontal coordinates are apparent topocentric coordinates. The ecliptic coordinates are apparent geocentric coordinates.

Display this dialog box by clicking on the moon with the right mouse button and then selecting the corresponding About command on the popup menu that appears, or by using the Solar System Object command on the Data menu.

OK

Click this button to close this dialog box.

Copy

Click this button to copy the data displayed in this dialog box onto the clipboard. After the data has been copied onto the clipboard, it can be pasted into an editor or word processor, and then saved to a file or printed. To align the data in an editor or word processor, specify a fixed-width font such as Courier New.

Help

Click this button to display Help for this dialog box.


Object Paths dialog box

Use the Object Paths dialog box to display the paths of solar system objects across the sky. The calculated positions along each path can optionally be marked and labeled.

Display the Object Paths dialog box by using the Object Paths command on the Chart menu.

Objects

Check the objects for which you'd like to calculate and display paths.

Calculate X positions along each path

Enter the number of positions to be calculated along each path.

Separate positions by X days

Enter the interval between calculated positions in days.

Label every X positions

Enter the interval between labeled positions. For example, enter "7" if you would like every seventh position to be labeled. Enter "0" if you don't want any positions to be labeled. Positions will only be labeled if one of the options in the Label with group is checked.

Mark all positions with a cross

Click this option if you want all calculated positions to be marked with a cross.

Mark all labeled positions with a cross

Click this option if you only want all labeled positions to be marked with a cross.

Label with

Check the type of information you'd like to see.

Date. This option causes a position to be labeled with the date on which the center of the object reaches the position.

Time. This option causes a position to be labeled with the time at which the center of the object reaches the position. The Time option is useful whenever you specify a fractional day between calculated positions. This is something you might want to do in the case of the moon, due to its rapid motion across the sky.

Label angle

Enter the angle of the labels, measured clockwise with respect to the normal text orientation. In other words, an angle of 0 degrees corresponds to horizontal text written from left to right, and an angle of 90 degrees corresponds to vertical text written from bottom to top.

OK

Click this button to close this dialog box and display the paths.

Cancel

Click this button to close this dialog box without displaying the paths.

Help

Click this button to display Help for this dialog box.


Page Setup dialog box

Use the Page Setup dialog box to specify the sizes of the margins around a printed sky chart and whether to print in black and white or in color.

The Page Setup dialog box is displayed whenever you print or preview a sky chart.

Caption

Enter any text you want to appear in the upper left corner of the printed sky chart.

Top, Bottom, Left, Right

Enter the sizes of the margin at the top, bottom, left, and right side of the page. The default margins are 0.75 inches or 1.905 centimeters.

The sizes of margins is specified in inches or in centimeters depending on the preference selected in the Windows Control Panel. To change these units, go to Control Panel, Regional Settings, select the Numbers tab, and then select either Metric (centimeters) or U.S. (inches) under Measurement system.

The sizes of margins are measure from the edge of the printed page.

Print in black and white

Check this box to print in black and white. Otherwise, sky charts will be printed in color. Printing in color can result in very nice sky charts even on black and white laser printers, because colors are converted to shades of gray on such printers.

OK

Click this button to close this dialog box and print or preview the page.

Cancel

Click this button to close this dialog box without printing or previewing the page.

Help

Click this button to display Help for this dialog box.


Planet Data dialog box

Use the Planet Data dialog box to display information about a planet. This information includes the planet's equatorial, horizontal, and ecliptic coordinates, distances from the earth and sun, elongation from the sun, angular diameter, magnitude, the constellation it is in, its rising, transit, and setting times, and the illumination of its disk. The equatorial and horizontal coordinates are apparent topocentric coordinates. The ecliptic coordinates are apparent geocentric coordinates.

Display this dialog box by clicking on the planet with the right mouse button and then selecting the corresponding About command on the popup menu that appears, or by using the Solar System Object command on the Data menu.

OK

Click this button to close this dialog box.

Copy

Click this button to copy the data displayed in this dialog box onto the clipboard. After the data has been copied onto the clipboard, it can be pasted into an editor or word processor, and then saved to a file or printed. To align the data in an editor or word processor, specify a fixed-width font such as Courier New.

Help

Click this button to display Help for this dialog box.


Planets Data dialog box

Use the Planets Data dialog box to display information about all planets visible from the earth. For each planet, this information includes the equatorial coordinates, the constellation it is in, distances from the earth and sun, angular diameter, magnitude, and its rising, transit, and setting times. The equatorial coordinates are apparent topocentric coordinates.

Display this dialog box by using the Planets command on the Data menu.

OK

Click this button to close this dialog box.

Copy

Click this button to copy the data displayed in this dialog box onto the clipboard. After the data has been copied onto the clipboard, it can be pasted into an editor or word processor, and then saved to a file or printed. To align the data in an editor or word processor, specify a fixed-width font such as Courier New.

Help

Click this button to display Help for this dialog box.


Seasons Data dialog box

Use the Seasons Data dialog box to view data about the seasons of the year. The beginning of each of the four seasons depends on the latitude of the current location. If the location is on or above the equator, spring starts in March, summer in June, fall in September, and winter in December. If the location is below the equator, spring starts in September, summer in December, fall in March, and winter in June.

Display the Seasons Data dialog box by using the Seasons command on the Data menu.

Local time

Specifies the local time at which the season begins.

Universal time

Specifies the universal time at which the season begins.

Julian date

Specifies the Julian date at which the season begins.

Duration

Specifies the duration of the season in days.

OK

Click this button to close this dialog box.

Copy

Click this button to copy the data displayed in this dialog box onto the clipboard. After the data has been copied onto the clipboard, it can be pasted into an editor or word processor, and then saved to a file or printed. To align the data in an editor or word processor, specify a fixed-width font such as Courier New.

Help

Click this button to display Help for this dialog box.


Select dialog box

Use the Select dialog box to select a star, deep sky object, constellation, solar system object, or point on the celestial sphere.

This dialog box is displayed when you use the Star, Deep Sky Object, Constellation, Solar System Object, or Point command on the Search menu, or the Solar System Object command on the Data menu.

OK

Click this button to close this dialog box and select the object.

Cancel

Click this button to close this dialog box without selecting the object.

Help

Click this button to display Help for this dialog box.


Solar System Objects dialog box

Use the Solar System Objects dialog box to set solar system object display options.

Display the Solar System Objects dialog box by using the Solar System Objects command on the Chart menu.

Solar system objects

Check this box to display solar system objects.

Labels

Check this box to display solar system object labels.

Label type

Select the type of label you'd like to see.

Abbreviations such as "Me" and "Ve". The Galilean satellites of Jupiter will be labeled "I" (Io), "II" (Europa), "III" (Ganymede), and "IV" (Callisto).

Names such as "Mercury" and "Venus".

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Star Data dialog box

Use the Star Data dialog box to display information about a star. This information includes the star's proper name, Bayer and Flamsteed designations, equatorial coordinates, horizontal coordinates, magnitude, the constellation it is in, its rising, transit, and setting times, and its spectral type.

Display this dialog box by clicking on the star with the right mouse button and then selecting the corresponding About command on the popup menu that appears.

OK

Click this button to close this dialog box.

Copy

Click this button to copy the data displayed in this dialog box onto the clipboard. After the data has been copied onto the clipboard, it can be pasted into an editor or word processor, and then saved to a file or printed. To align the data in an editor or word processor, specify a fixed-width font such as Courier New.

Help

Click this button to display Help for this dialog box.


Stars dialog box

Use the Stars dialog box to set star display options. The registered version of CyberSky includes 80,179 stars to magnitude 8.5, but the shareware version includes only 1,671 stars to magnitude 5.0. With your naked eyes you can generally see stars of the fourth or even fifth magnitude from urban locations, and can see stars of the sixth magnitude when you are far away from city lights. The registered version of CyberSky can show you many more stars visible through binoculars or a telescope.

Display the Stars dialog box by using the Stars command on the Chart menu, or by clicking the Data bar pane that displays the limiting magnitude for stars.

Stars

Check this box to display stars.

Star sizes

Select the sizes of symbols you'd like to see stars represented by.

Largest displays stars using the largest symbols.

Larger displays stars using larger than normal symbols.

Normal displays stars using normal symbols.

Labels

Check this box to display star labels.

Label type

Select the type of label you'd like to see.

Proper names such as "Betelgeuse" and "Rigel". If a star does not have a proper name, no label will be displayed.

Bayer letters such as "α" for Betelgeuse and "β" for Rigel. If a star does not have a Bayer designation, no label will be displayed.

Flamsteed numbers such as "58" for Betelgeuse and "19" for Rigel. If a star does not have a Flamsteed designation, no label will be displayed.

Magnitudes such as "0.50" for Betelgeuse and "0.12" for Rigel.

Automatic

Check this box to have CyberSky automatically adjust the limiting magnitude for you. The limiting magnitude will increase when you zoom in, and will decrease when you zoom out.

Magnitude

Move the slider left to include fewer stars in the chart, or right to include more stars.

Colors based on spectral types

Check this box to display stars in colors based on their spectral types.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Sun Data dialog box

Use the Sun Data dialog box to display information about the sun. This information includes the sun's equatorial, horizontal, and ecliptic coordinates, distance from the earth, angular diameter, magnitude, the constellation it is in, its rising, transit, and setting times, and its spectral type. The equatorial and horizontal coordinates are apparent topocentric coordinates. The ecliptic coordinates are apparent geocentric coordinates.

Display this dialog box by clicking on the sun with the right mouse button and then selecting the corresponding About command on the popup menu that appears, or by using the Solar System Object command on the Data menu.

OK

Click this button to close this dialog box.

Copy

Click this button to copy the data displayed in this dialog box onto the clipboard. After the data has been copied onto the clipboard, it can be pasted into an editor or word processor, and then saved to a file or printed. To align the data in an editor or word processor, specify a fixed-width font such as Courier New.

Help

Click this button to display Help for this dialog box.


Time Step dialog box

Use the Time Step dialog box to specify the size of the time step between animation frames.

Display the Time Step dialog box by using the Time Step command on the Animation menu, or by pressing the Ctrl+T keys.

Factor

Enter the factor by which to multiple the selected units on the right.

Units

Select the units you want to multiply by the factor on the left.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Twilight Data dialog box

Use the Twilight Data dialog box to view the times at which astronomical, nautical, and civil twilight begin and end, as well as the times of sunrise and sunset.

Display the Twilight Data dialog box by using the Twilight command on the Data menu.

OK

Click this button to close this dialog box.

Copy

Click this button to copy the data displayed in this dialog box onto the clipboard. After the data has been copied onto the clipboard, it can be pasted into an editor or word processor, and then saved to a file or printed. To align the data in an editor or word processor, specify a fixed-width font such as Courier New.

Help

Click this button to display Help for this dialog box.


Universal Time dialog box

Use the Universal Time dialog box to change the universal date and time.

Display the Universal Time dialog box by using the Universal Time command on the Time menu, by clicking the Data bar pane that displays the universal time, or by pressing the Ctrl+U keys.

Date

To specify the universal date, enter month, day, and year numbers into the three boxes or click the spin buttons to change the displayed date. Years must fall in the range 4000 BC to 4000 AD. October 4, 1582 and earlier dates are on the Julian calendar. October 15, 1582 and later dates are on the Gregorian calendar.

The format in which dates are entered and displayed is based on the format specified in the Windows Control Panel under Regional Settings, Date.

Month/day/year format

Day/month/year format

Year/month/day format

Time

To specify the universal time, enter hours, minutes, and seconds into the three boxes or click the spin buttons to change the displayed time.

The format in which times are entered and displayed is always the 24-hour format.

24-hour format

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


Zoom Level dialog box

Use the Zoom Level dialog box to set the magnification for the sky chart.

Display the Zoom Level dialog box by using the Zoom Level command on the View menu, or by clicking the Data bar pane that displays the zoom level.

Zoom level

Select one of the options in this box to set the zoom level.

OK

Click this button to close this dialog box and save any changes you've made.

Cancel

Click this button to close this dialog box without saving any changes you've made.

Help

Click this button to display Help for this dialog box.


The sky at the North Pole, equator, and South Pole

While performing this exploration, you'll observe the sky visible from the earth's North Pole, equator, and South Pole.

Make sure the Horizon Mode option on the Chart menu is selected and the Horizon option on the same menu is checked. Click the [image] button on the View toolbar to bring the south point to the bottom of the sky chart, and then click the [image] button on the same toolbar to display the entire sky visible at the current viewing location. The center of the circle you see corresponds to the zenith, the point directly above your head, and the bottom of the circle is the south point on the horizon.

Now make sure the Daylight option on the Options menu is checked. When this option is turned on, the color of the sky background varies depending on the altitude of the sun. Set the location to "North Pole" using the Location command on the Options menu. After you've moved your viewing location to the North Pole, use the Midnight command on the Time menu to set the local time to midnight. Depending on the time of year, you may be surprised to find that the sun is above the horizon and it is daytime, even though the local time is midnight.

Notice a star of average brightness located almost exactly at the center of the sky chart. This star is called Polaris, or simply the North Star. Polaris just happens to be located close to the north celestial pole, the projection of the earth's North Pole onto the celestial sphere. When you look straight up at the zenith while standing at the North Pole, you are looking along the earth's axis of rotation, and therefore toward Polaris.

Display the celestial equator by clicking the [image] button on the Chart toolbar. The celestial equator is the projection of the earth's equator onto the celestial sphere, and lies 90 degrees from the north and south celestial poles. Because the north celestial pole is directly overhead at the North Pole, the celestial equator coincides with the horizon. Atmospheric refraction causes objects near the horizon to appear slightly higher than they really are, which explains why CyberSky shows the celestial equator slightly above the horizon.

From any location on the earth's surface you can see only half of the celestial sphere at any given time. As you can see, at the North Pole you can only observe that part of the celestial sphere that is north of the celestial equator. Any celestial objects that are south of the celestial equator -- those that have negative declinations -- are below the horizon and cannot be seen. This means that an observer at the North Pole can only see the "top" part of the constellation Orion, and can never see the constellation Scorpius.

A small cross at the center of the sky chart, labeled "NCP", marks the north celestial pole. Click the [image] on the View toolbar to zoom in so you can see that Polaris is not located exactly at the north celestial pole. You will probably need to zoom in three or four times to see this clearly. Click the [image] on the View toolbar when you're ready to restore your view of the entire sky.

Use the Time Step command on the Animation menu to set the animation time step to five minutes. Click the [image] button on the Animation toolbar to start animation. Notice that all of the stars appear to be moving in circles, counterclockwise, around Polaris. Here at the North Pole, all stars are circumpolar; they are above the horizon all day long. Click the [image] button on the Animation toolbar when you're ready to stop animation.

Display the ecliptic by clicking the [image] button on the Chart toolbar. The ecliptic is the projection of the earth's orbit onto the celestial sphere, which means that the sun appears to move along this line during the course of a year. Because the earth's axis is tilted by about 23.5 degrees with respect to its orbit around the sun, the celestial equator and ecliptic are tilted by about 23.5 degrees with respect to each other. The celestial equator and ecliptic cross at two points on opposite sides of the sky. Part of the ecliptic lies to the north of the celestial equator and the other part lies to the south.

Now use the Time Step command on the Animation menu to set the animation time step to five solar days. Click the [image] button on the Animation toolbar to start animation. Watch the motion of the sun carefully. If you don't see the sun moving along the ecliptic, wait for it to appear. It is important to realize that you are not watching the sun move across the sky over the course of a day. Each animation step shows you the sky at the same time of day, and each step is separated by five full days. As you can see, here at the North Pole the sun spends half a year above the horizon. The North Pole experiences six months of daytime!

Click the [image] button on the Animation toolbar while the sun is in the sky, and then use the Time Step command on the Animation menu to set the animation time step to back to five minutes. Click the [image] button on the Animation toolbar to start animation once again, and observe how the sun circles the sky. When you're ready to continue, click the [image] button on the Animation toolbar.

Set the location to "Equator" by using the Location command on the Options menu. At the North Pole the north celestial pole was directly overhead. Here at the equator the celestial equator crosses the sky from due east to due west and passes through the zenith. The north celestial pole is at the north point on the horizon, and the south celestial pole is at the south point.

Click the [image] button on the Animation toolbar to start animation. The time step should still be set at five minutes. Here at the equator all of the stars rise in the east, move across the sky, and then set in the west. There are no circumpolar stars. Over the course of a day you can see the entire celestial sphere. Click the [image] button on the Animation toolbar.

Set the location to "South Pole" by using the Location command on the Options menu. The situation at the South Pole is similar to the situation you saw at the North Pole, but here it is the south celestial pole that is directly overhead. Notice that there is no star that marks the position of the south celestial pole the way Polaris marks the position of the north celestial pole.

As you can see, at the South Pole you can only observe that part of the celestial sphere that is south of the celestial equator. Any celestial objects that are north of the celestial equator -- those that have positive declinations -- are below the horizon and cannot be seen. This means that an observer at the South Pole can only see the "bottom" part of the constellation Orion, and can never see the constellation Gemini.

Click the [image] button on the Animation toolbar to start animation. The time step should still be set at five minutes. Notice that all of the stars appear to be moving in circles, clockwise, around the south celestial pole. Here at the South Pole, all stars are circumpolar, just as they were at the North Pole. But, the stars visible at the North Pole can never be seen at the South Pole, and vice versa. Click the [image] button on the Animation toolbar.

Once again, use the Time Step command on the Animation menu to set the animation time step to five solar days. Click the [image] button on the Animation toolbar to start animation. As was the case at the North Pole, you'll find that the sun spends half a year above the horizon. The South Pole experiences six months of daytime just as the North Pole does. But, when it is daytime at the South Pole it is nighttime at the North Pole, and vice versa. Click the [image] button on the Animation toolbar when you're ready to finish this exploration.

Use the Return Home command on the Options menu when you're ready to leave the South Pole and return to your home location.


Solar days and sidereal days

While performing this exploration you'll learn about solar days and sidereal days and see how they differ.

Solar time is time measured with respect to the motion of the sun. The clocks we use for civil timekeeping are based on solar time. Of course, the apparent motion of the sun across the sky is actually caused by the rotation of the earth. So, our clocks measure the length of time required for the earth to rotate once with respect to the sun. From our perspective, the sun revolves around the earth every 24 hours. This period is known as a solar day.

Sidereal time is time measured with respect to the motion of the stars. The apparent motion of the stars across the sky is also caused by the rotation of the earth. But, while the earth is rotating on its axis it is also moving along its orbit around the sun. Over the course of a day the earth moves about one degree along its orbit (360 degrees in a full orbit divided by 365 days in a year is about one degree). Therefore, from our perspective, the sun moves about one degree from west to east with respect to the background stars.

All of this means that according to our clocks, which are based on solar time, a given star will rise or set about four minutes earlier each day (the earth rotates about 15 degrees in one hours, so one degree of rotation is equivalent to about four minutes of time). For example, a star that rises at 9:00 PM (21:00) tonight will rise at 8:56 PM (20:56) tomorrow and at 8:52 PM (20:52) the next night. One month later that star will rise or set two hours earlier. In other words, from our perspective, the stars revolve around the earth in only 23 hours and 56 minutes. This period is known as a sidereal day.

Make sure the Horizon Mode option on the Chart menu is selected and the Horizon option on the same menu is checked. Click the [image] button and then the [image] button on the View toolbar. This tells CyberSky to display a view of the entire sky with the south horizon at the bottom of the display. Now set the time to noon using the Noon command on the Time menu.

You should now see the sun at its noontime position. Use the Time Step command on the Animation menu to set the animation time step to one solar day. Then click the [image] button on the Animation toolbar to start animation. If you look at the local time displayed at the top of the Data bar you'll see that the time is not changing but the date is advancing one day per animation step.

As the days rush by and your viewpoint moves around the sun, your line of sight remains fixed toward the sun. The sun moves north and south due to the tilt of the earth's axis and east and west due to the fact that the earth's orbit is an ellipse rather than a circle. If the earth's axis wasn't tilted and its orbit was a circle, the sun would be motionless in the display. The stars, on the other hand, are scrolling from east to west at a steady rate.

Now use the Time Step command on the Animation menu again, this time to set the animation time step to one sidereal day. If you look at the local time displayed in the legend you'll see that the date is advancing one day per animation step but the time is about four minutes earlier at each step.

Your line of sight now remains fixed toward the stars, so they are motionless in the display. As your viewpoint moves around the sun, solar system objects move in and out of view.

As is the case with solar days, sidereal days are also divided into hours, minutes, and seconds. Naturally, these hours, minutes, and seconds are shorter than the solar hours, minutes, and seconds you're familiar with. One solar day is 24 solar hours long, and one sidereal day is 24 sidereal hours long, but one sidereal day is 23 solar hours and 56 solar minutes long.


Sirius, the Dog Star

While performing this exploration you'll observe the heliacal rising of the star Sirius.

The "dog days of summer" are named after Sirius, the brightest star in the constellation Canis Major, the Great Dog. The star's proper name is probably derived directly from the Greek word for "sparkling" or "scorching". Sirius is the brightest star in the sky other than the sun, and is a dazzling sight on a clear, frosty winter night. The ancient Egyptians revered Sirius, as it was associated with the goddess Isis, wife of Osiris and mother of Horus. The southern shaft of the Queen's Chamber in the great pyramid of Khufu points directly toward Sirius at its meridian transit. Many Egyptian temples were aligned in such a way that the light of Sirius could reach the inner chambers.

As the sun moves along the ecliptic over the course of a year, stars that are near the sun become impossible to see due to its brilliance. That is, the sun will hide a given star for a period of time. Eventually the sun moves far enough from the star that it can be seen briefly just before the sun rises. This first appearance of a star just before sunrise is referred to as the star's heliacal rising.

Thousands of years ago, accurate timekeeping required careful observation of the skies. The date of Sirius' heliacal rising was very important to the ancient Egyptians, as it coincided with the annual flood of the Nile on which Egyptian agriculture depended. The ancient Greeks, seeing that the sun and Sirius both traveled across the sky during daylight hours, believed that their combined light actually caused the hot weather of summer.

Make sure the Horizon Mode option on the Chart menu is selected and the Horizon option on the same menu is checked. Click the [image] button on the View toolbar to view the sky visible above the east horizon. Set the location to "Egypt, Luxor" using the Location command on the Options menu. Click the [image] button on the Animation toolbar to set the date to June 20, 3000 BC. Then set the time to sunrise using the Sunrise command on the Time menu.

You are now looking at the sky visible from southern Egypt about 5,000 years ago! The sun has just risen on the left side of the display. The constellation Orion is visible on the right side of the display. Sirius will rise just below Orion, but will not be visible on this date because the sun has already risen.

Click the [image] button on the Animation toolbar again and set the date to June 30, 3000 BC. Then set the time to sunrise again using the Sunrise command on the Time menu. You should be able to see that both the sun and Sirius are above the horizon, and that Sirius is slightly higher than the sun. This means that Sirius had risen and was visible for five or six minutes before sunrise. Adjust the local time to verify this.

Use the Return Home command on the Options menu when you're ready to leave Aswan and return to your home location.


Precession of the equinoxes

While performing this exploration you'll observe the effect of precession of the equinoxes on the appearance of the sky.

The earth is not a perfect sphere, but has an equatorial diameter that is slightly larger than its polar diameter. The sun, moon, and other planets exert a gravitational attraction on the earth's equatorial bulge, which causes the earth's axis of rotation to wobble, just as a spinning top wobbles. The positions of the celestial poles therefore move across the sky, tracing out circles 47 degrees across every 25,800 years. The ecliptic and celestial equator cross at two points, known as the vernal and autumnal equinoxes. The positions of these points also move around the sky every 25,800 years, giving this effect the name "precession of the equinoxes".

The fact that the earth's axis of rotation wobbles means that the star we call the North Star was not near the north celestial pole thousands of years ago, and will not be near the pole thousands of years in the future! Precession of the equinoxes does not alter the constellation outlines or change their boundaries with respect to the stars, but causes a slow drift of the entire celestial coordinate system on the celestial sphere.

Click the [image] button on the View toolbar, and then use the Zoom Level command on the View menu to set the zoom level to 4. Set the location to "North Pole" using the Location command on the Options menu. You are now looking straight up at the zenith. When you do this at the North Pole, you are looking along the earth's axis of rotation. The star you see at the center of the sky chart is Polaris, the North Star.

Click the [image] button on the Chart toolbar to display constellation figures. Use the Current Time command on the Time menu. Then use the Time Step command on the Animation menu to set the animation time step to five minutes. Click the [image] button on the Animation toolbar to start animation. Notice that all of the stars appear to be moving in circles, counterclockwise, around Polaris.

Now set the year to 2450 BC by using the Local Time command on the Time menu. Suddenly, Polaris is no longer at the center of the sky chart. The star that is now located at the zenith is Thuban, a star of the constellation Draco. All of the stars now appear to be moving in circles around Thuban, including Polaris! Click the [image] button on the Animation toolbar when you're ready to stop animation.

As you can see, Thuban was the pole star at the time the great pyramid of Khufu was built in ancient Egypt. In fact, the northern shaft of the King's Chamber in the pyramid points directly toward Thuban at its upper meridian transit.

Click the [image] button on the Chart toolbar to display the celestial equator and the celestial poles. The celestial equator will not be visible in this view of the sky, but the north celestial pole will be marked by a cross labeled "NCP". Note that Thuban is not located exactly at the north celestial pole. You may wish to adjust the date forward or backward 25 or 50 years at a time to see when Thuban was closest to the pole. Thuban's closest distance to the pole was about half a degree, which is also the closest distance between the pole and the current pole star, Polaris.

About 5,500 years from now the star Alderamin will come within about four degrees of the pole. About 12,000 years from now the star Vega will also come within about four degrees of the pole.

Use the Return Home command on the Options menu when you're ready to leave Stuttgart and return to your home location.


The proper motion of Arcturus

While performing this exploration you'll observe the proper motion of the star Arcturus, the brightest star in the constellation Bootes.

All stars move through space, just as our sun does, but those that are close to our solar system appear to move much faster than those that are farther away. Even the closest stars outside the solar system are very far away, and detecting their proper motions requires very large telescopes and very sensitive equipment. The proper motion of a star during the course of a human lifetime results in a very small angular shift. But, the effect does accumulate over thousands of years.

Make sure the Atlas Mode option on the Chart menu is selected. Use the Zoom Level command on the View menu to set the zoom level to 8. Click the [image] button on the Chart toolbar to display constellation figures. Click the [image] button on the Animation toolbar to set the date to January 1, 2000 and the time to midnight. Use the Star command on the Search menu to search for Arcturus.

When CyberSky calculates the positions of the stars, it takes their individual proper motions into account, as well as the effect of precession. However, CyberSky does not apply proper motion calculations to the constellation figures. In other words, the constellation figures are attached to the equatorial coordinate system rather than to individual stars. This means constellation figures do not distort due to proper motion; you can observe proper motion by watching stars move with respect to constellation figures.

You should now see Arcturus at the center of the sky chart. Note its position with respect to the constellation figure for Bootes. Click the [image] button on the Animation toolbar to change the year to 2000 BC. Arcturus will no longer be at the center of the sky chart, so use the Star command on the Search menu to search for it.

As you can see, Arcturus has moved by over two degrees in the last 4,000 years. Muphrid, southwest of Arcturus, has moved less than a quarter of this angle in the same period of time. The English astronomer Edmund Halley, famous for the comet that bears his name, discovered proper motion. He noticed that Arcturus was not at the same location it was shown at in star charts made 2,000 years earlier by the Greek scholar Hipparchus.


The sun, the ecliptic, and the seasons

While performing this exploration, you'll follow the sun's motion along the ecliptic and see how its changing position causes the seasons.

Make sure the Horizon Mode option on the Chart menu is selected and the Horizon option on the same menu is checked. Click the [image] button and then the [image] button on the View toolbar. This tells CyberSky to display a view of the entire sky with the south horizon at the bottom of the display. Click the [image] button on the Animation toolbar to set the date to March 21 and the time to noon.

You should now see a full-sky view with the sun at its noontime position. Display the celestial equator by clicking the [image] button on the Chart toolbar. The celestial equator is the projection of the earth's equator onto the celestial sphere. If you're watching the sky from north of the equator, you'll see the celestial equator arc across the southern part of the sky. If you're watching the sky from the equator, you'll see the celestial equator pass through the zenith. If you're watching from south of the equator, you'll see the celestial equator arc across the northern part of the sky.

Next, display the ecliptic by clicking the [image] button on the Chart toolbar. The ecliptic is the projection of the earth's orbit onto the celestial sphere. Therefore, the sun will appear to move along this line during the course of a year. Because the earth's axis is tilted by about 23.5 degrees with respect to its orbit around the sun, the celestial equator and ecliptic are tilted by about 23.5 degrees with respect to each other. This means the celestial equator and ecliptic cross at two points on opposite sides of the sky. Notice that the sun is located near one of these points. When the sun reaches this point, called the vernal equinox, it marks the beginning of spring in the Northern Hemisphere and fall in the Southern Hemisphere.

Use the Time Step command on the Animation menu to set the animation time step to one solar day. Click the [image] on the Animation toolbar and watch what happens. Click the button a few more times. Each time you click the button the date advances by one day, but the time remains set to noon. You can see that as each day passes the sun moves a small distance -- about one degree -- along the ecliptic. This causes the sun's noontime position to be farther and farther north every day. Now click the [image] button on the Animation toolbar and continue to watch the motion of the sun along the ecliptic.

The sun continues to move northward along the ecliptic until it reaches the northernmost point on June 21. When the sun reaches this point, called the summer solstice, it marks the beginning of summer in the Northern Hemisphere and winter in the Southern Hemisphere. After the sun passes the summer solstice it moves southward until it crosses the celestial equator. When the sun reaches this point, called the autumnal equinox, it marks the beginning of fall in the Northern Hemisphere and spring in the Southern Hemisphere. The sun continues to move south along the ecliptic until it reaches the southernmost point on December 21. When the sun reaches this point, called the winter solstice, it marks the beginning of winter in the Northern Hemisphere and summer in the Southern Hemisphere. After the sun passes the winter solstice it moves northward until it returns to the vernal equinox on March 21.

If the earth's axis was not tilted with respect to its orbit, the celestial equator and ecliptic would follow the same path across the sky, and we would not experience seasons. Some people believe we experience seasons because the earth is closer to the sun during the summer than it is during the winter. The earth does orbit the sun in an elliptical path, but it is slightly closer to the sun during January than it is during June! If the earth's changing distance from the sun was responsible for the seasons, the Northern and Southern hemispheres would experience the same season at the same time, but they don't.

The reason we experience seasons has to do with how much sunlight the ground absorbs at different times of the year. At the summer solstice the sun is higher in the sky than it is during the rest of the year, so the ground absorbs more than the average amount of sunlight. The sun's rays hit the ground at a higher angle and are therefore more concentrated than they are during the winter. Also, the sun is above the horizon for a longer time during the summer, so the ground has more time to absorb the sun's light. On the other hand, at the winter solstice the sun is lower in the sky than it is during the rest of the year, so the ground absorbs less than the average amount of sunlight. The sun's rays hit the ground at a lower angle and are therefore less concentrated than they are during the summer. And, the sun is above the horizon for a shorter time during the winter, so the ground has less time to absorb the sun's light.


The analemma and the equation of time

While performing this exploration you'll observe the sun at the same time of day over the course of a year and see the figure eight it traced out on the sky. This figure eight, called the analemma, can sometimes be seen on a globe, map, or the face of a sundial.

The earth's axis of rotation is tilted by about 23.5 degrees with respect the plane of its orbit around the sun. The sun reaches its farthest distance north of the celestial equator on the summer solstice, and its farthest distance south on the winter solstice. On the vernal equinox the sun is on the celestial equator; the same is true on the autumnal equinox. An observer at temperate latitudes will see the sun cross the sky in a high arc during the summer and in a low arc during the winter. An observer in the tropics will see the sun cross the meridian north of the zenith during summer and south of the zenith during winter.

The earth's orbit around the sun is an ellipse, not a perfect circle. The earth's orbital speed is fastest when it is nearest to the sun, and slowest when it is farthest from the sun. This variation in orbital speed causes the sun's motion along the ecliptic to vary in speed. This means that the length of the day as measured by a sundial actually varies throughout the year. On the other hand, clocks measure even intervals of time throughout the year. Sundials measure apparent solar time whereas clocks measure mean solar time. The "equation of time" is the amount of time that must be added to mean solar time to obtain apparent solar time. In other words, it is the difference between time measured by a sundial and by a clock.

Make sure the Horizon Mode option on the Chart menu is selected. Set the location to "Los Angeles" using the Location command on the Options menu. Click the [image] button on the View toolbar to view the sky visible above the south horizon.

Click the [image] button on the Animation toolbar to set the date to March 21 and the time to noon. You should now see the sun near the center of the sky chart. Set the animation time step to five solar days by using the Time Step command on the Animation menu. If you have a fast computer, you may want to try a smaller time step such as two or three solar days. Click the [image] button on the Animation menu to start animation.

Each animation step shows the sun at noon as measured by a clock. It's important to realize that the motion of the stars you're seeing is not the familiar motion due to the earth's rotation on its axis. The stars appear to be moving past the sun because the earth is moving around the sun. By setting the animation time step to an integral number of solar days, you've effectively eliminated the effect of the earth's rotation so you can concentrate on the effect of the earth's revolution around the sun.

Watch the motion of the sun carefully and ignore everything else. Each day the sun will move farther north until it reaches its highest point on or near June 21, the summer solstice. It will then move southward, passing through the center of the figure eight on or near the autumnal equinox, September 23. On or near December 21, the winter solstice, the sun will reach its lowest point, and will begin to move northward again.

Use the Return Home command on the Options menu when you're ready to leave Los Angeles and return to your home location.


The conjunction of Venus and Jupiter on June 17, 2 BC

While performing this exploration you'll watch the conjunction of the planets Venus and Jupiter that took place on June 17, 2 BC.

Make sure the Horizon Mode option on the Chart menu is selected and the Horizon option on the same menu is checked. Set the location to "Iran, Tehran" using the Location command on the Options menu. Then click the [image] button on the View toolbar to see the sky visible above the west horizon. Click the [image] button on the Animation toolbar to set the date to June 7, 2 BC and the time to 9:00 PM (21:00).

You're now seeing the western sky as it appeared a couple of hours after sunset on a day two thousand years in the past! The two brightest planets in the sky, Venus and Jupiter, are visible on either side of the star Regulus, the brightest star in the constellation Leo. If you can't see the moon and planets in the display, click the [image] button on the Chart toolbar to turn them on!

Click the [image] button on the Animation toolbar ten times, until the local date reads June 17, 2 BC. Notice that every day Venus and Jupiter move closer together until they appear to overlap. The zoom level is currently set to 2X, so CyberSky is not displaying the planetary disks to scale. In other words, the disks appear to overlap but they may not be as close together as you think.

To get a better look, click the [image] button on the Search toolbar to move Venus to the center of the sky chart. Then click the [image] button on the Chart toolbar eight times, until the zoom level reads 512X. Now you can see Jupiter's Galilean satellites. This would have been a spectacular view through a telescope! Venus and Jupiter were so close to each other in the sky that to the naked eye they would have appeared as a single, very bright object.

According to the Bible, three Magi, members of a priestly caste in ancient Persia (modern Iran) were guided to Bethlehem by a "star" to worship the infant Jesus. This conjunction of Venus and Jupiter has been suggested as one possible explanation of the Star of Bethlehem.

A similar conjunction of Venus and Jupiter, but visible in the eastern sky before dawn, took place only ten months earlier. You should have no trouble verifying this for yourself. Set the date to August 12, 3 BC and the time to sunrise. View the sky above the east horizon.

Use the Return Home command on the Options menu when you're ready to return to your home location.


The transit of Venus on June 3, 1769

While performing this exploration you'll watch the transit of the planet Venus that took place on June 3, 1769.

The term transit has two meanings in astronomy: the passage of a celestial body across the meridian, and the passage of a small celestial body in front of a much larger one. The latter meaning applies here; you'll watch the disk of Venus move across the face of the sun. Transits of Venus take place in pairs, with each transit separated by eight years and each pair separated by over 100 years.

Make sure the Atlas Mode option on the Chart menu is selected. Set the location to "France, Tahiti, Papeete" using the Location command on the Options menu. Tahiti is an island in the South Pacific, part of French Polynesia, an overseas territory of France. Click the [image] button on the Search toolbar to move the sun to center of the sky chart. Then click the [image] button on the Animation toolbar to set the date to June 3, 1769 and the time to 9:00 AM (9:00). Use the Zoom Level command on the View menu to set the zoom level to 256X.

You should see Venus close to the edge of the sun's disk. Set the animation time step to ten minutes by using the Time Step command on the Animation menu. If you have a fast computer, you may want to try a smaller time step such as 5 minutes. Click the [image] button on the Animation menu to start animation. The transit starts at about 9:20 AM (9:20) and ends at about 3:30 PM (15:30).

Captain James Cook (1728-1779) made his famous first voyage to the South Pacific primarily to bring astronomers of the Royal Society to Tahiti to observe this transit. They left Plymouth, England in August 1768 and arrived at Tahiti in April 1769, which plenty of time to spare before the transit took place.

What was the point of traveling to Tahiti to observe this transit of Venus? The laws of planetary motion formulated by Johannes Kepler (1571-1630) allowed astronomers to determine the relative distances of the planets. That is, they had been able to determine the distances of the planets in astronomical units. An astronomical unit is simply the distance between the earth and the sun. Astronomers could say that the sun is one astronomical unit from the earth, and that Jupiter is about five astronomical units from the sun. But, they didn't know these distances in absolute units such as kilometers or miles.

Astronomers had long been attempting to determine the sun's parallax, the shift in its position when viewed from widely separated places. To understand this effect, hold your thumb at arm's length in front of your face, and then look at your thumb first with one eye, and then with the other. As you switch from one eye to the other you'll see your thumb's position shift in relation to objects that are farther away. Because you're eyes are separated by a small distance, when you switch from one eye to the other you're actually seeing your thumb from a slightly different direction. Repeat this experiment, but hold you thumb closer to your face. You'll see that the shift in your thumb's position will be larger than it was before.

By watching this transit of Venus from different locations on the earth's surface, and recording the positions of Venus over the solar disk, the sun's parallax could be calculated and the true dimensions of the solar system could be known. Transits of Venus occurred on June 5, 1761 and June 3, 1769. Expeditions were sent around the world to record these transits. Charles Mason and Jeremiah Dixon, who later surveyed the Mason-Dixon Line, observed the 1761 transit from South Africa. Others observed this transit from Canada, Siberia, and Madagascar. When the data from all these observations was analyzed, the calculated parallax varied between 8.55 and 8.88 arc seconds. The modern accepted value is 8.79 arc seconds.

After the transit of Venus, Cook followed his secret orders to try to find a continent that had been suspected to exist in the South Pacific. In October 1769 a new land was discovered and named New Zealand. Cook spent half a year circumnavigating and mapping New Zealand before sailing westward. In April 1770 Cook discovered the east coast of a much larger land, which he named New South Wales. Cook spent months charting about 2,000 miles of what we now call Australia before heading to the Dutch settlement of Batavia and then back to England. Cook made two other voyages to the Pacific. He was killed by native inhabitants of Hawaii in February 1779.

The next transits of Venus will occur on June 7, 2004 and June 5, 2012.


The solar eclipse of August 11, 1999

While performing this exploration you'll be able to observe the total solar eclipse visible from Europe on August 11, 1999.

A solar eclipse can only occur when the moon is new. The moon's orbit is inclined about five degrees with respect to the ecliptic and intersects the ecliptic at two points known as the nodes of the orbit. If the moon's orbit was not inclined to the ecliptic, we would observe solar eclipses every month because the moon would pass over the sun's disk every month. But, because the moon's orbit is inclined by five degrees, most of the time the moon passes above or below the sun. An eclipse occurs only when the moon and the sun are both near one of the nodes of the moon's orbit.

The moon casts a shadow, and when this shadow sweeps across the surface of the earth people in the shadow see an eclipse. Observers in the area swept across by the umbra, the darkest part of the shadow, see a total solar eclipse. The solar disk is completely blocked in this case, allowing view of the sun's chromosphere, corona, and prominences. The moon's umbra is only about 270 kilometers (168 miles) across and moves so quickly that a total solar eclipse typically lasts only 3 or 4 minutes. The area surrounding the umbra is called the penumbra, and observers in the area swept across by the penumbra see only a partial eclipse. An annular eclipse occurs when the moon is farther than normal from the earth, and is therefore too small to completely cover the sun. When the moon passes in front of the sun observers see a ring (annulus) of sun surrounding the moon's disk.

It is a remarkable coincidence of nature that the sun and moon are nearly the same size in the sky. The sun is about 400 times larger than the moon, but it is also about 400 times farther way from the earth. It is a fact that the moon is slowly moving away from the earth, so sometime in the distant future total solar eclipses will no longer be possible.

Set the location to "Germany, Stuttgart" using the Location command on the Options menu. Make sure the Atlas Mode option on the Chart menu is selected. Click the [image] button on the Animation toolbar to set the date to August 11, 1999 and the time to 11:00 AM (11:00). Make sure the Daylight saving time option is checked. Use the Zoom Level command on the View menu to set the zoom level to 64. Click the [image] button on the Search toolbar to move the sun to the center of the sky chart.

You should now see the sun and moon very close to each other. Set the animation time step to one minute by using the Time Step command on the Animation menu. The sun is currently locked to the center of the display -- a result of using the program's search feature -- so when you start animation it will remain at the center of the display. Click the [image] button on the Animation menu to start animation.

The moon will move toward the sun and the two disks will touch at about 11:15 AM (11:15). This moment is called first contact. The moon will completely cover the solar disk from about 12:34 PM (12:34) to 12:37 PM (12:37). Last contact will take place at about 1:57 PM (13:57). Click the [image] button on the Animation toolbar when you're ready to finish this exploration.

Use the Return Home command on the Options menu when you are ready to leave Stuttgart and return to your home location.


The planetary alignment of May 5, 2000

While performing this exploration you'll watch an interesting planetary alignment you may have heard about.

Because the sun, moon, and planets move across the sky in a relatively narrow band centered on the ecliptic, and because they move at different rates, they will occasionally congregate in the same region of the sky. Such events, frequently referred to as planetary alignments, are also called conjunctions. Contrary to popular belief, during such alignments the sun, moon, and planets are not positioned along a straight line.

Planetary alignments have happened many times in the past and will happen many times in the future. Some people claim that during the next such event, which occurs in the year 2000, the summed gravitational forces of the sun, moon, and planets will result in natural disasters such as earthquakes, volcanoes, and tidal waves. This makes no sense. Relatively simple mathematics can be used to show that the gravitational forces due to the planets are insignificant compared with the normal tidal force due to the moon. If such alignments could trigger natural disasters on the earth, we would have records of such disasters coinciding with past alignments.

Make sure the Atlas Mode option on the Chart menu is selected. Click the [image] button on the Animation toolbar to set the date to May 2, 2000 and the time to noon. Use the Zoom Level command on the View menu to set the zoom level to 4. Click the [image] button on the Search toolbar to move the sun to the center of the display. You should now be able to see the sun, moon, and all five planets visible without optical aid. Mars is located farthest to the east, just below the Pleiades star cluster in the constellation Taurus. Saturn, Jupiter, the sun, Mercury, and Venus are all found within the constellation Aries. The moon is located farthest to the west in the constellation Pisces.

Advance the date to May 6, 2000 by clicking the [image] button on the Animation toolbar four times. Between May 2 and May 6 the moon will move from the west side of the grouping of objects to the east side. During this same period of time Venus will move closer to the sun, causing the entire grouping to compress into an even smaller angular span.

On May 5 (universal time), the sun, moon, and all five classical planets will occupy their smallest span of ecliptic longitude. Because this span is only about 26 degrees in size and is roughly centered on the sun, you won't be able to see this alignment in the real sky. The moon and Mars will be only about 16 degrees from the sun, in the morning sky. Venus will be a mere 10 degrees from the sun, in the evening sky. Mercury, Jupiter, and Saturn will be too close to the sun to be visible.

A similar alignment of these seven objects last occurred on February 5, 1962. Go ahead and change the date right now to see what it looked like! After the alignment of the year 2000, the next alignment will take place on March 20, 2675. Be sure to take a look at this one, too! There were a total of ten alignments between the years 1000 and 2000 during which the sun, Mars, Jupiter, and Saturn came within 10 degrees of each other. Given that there were no natural disasters recorded as a result of these conjunctions, it is reasonable to assume that we are in no danger from the alignment of the year 2000.


Retrograde motion of an inferior planet

While performing this exploration you'll observe the retrograde motion of the planet Venus.

Venus' orbit lies inside that of the earth, which is why Venus is referred to as an "inferior" planet. With respect to the sun, the center of our solar system, Venus' orbit is "below" that of the earth. Planets that are closer to the sun move more quickly than planets that are farther away. Venus therefore moves more quickly along its orbit than the earth, and at some point Venus will catch up to and move past the earth. This happens when the earth is near opposition as viewed from Venus, that is, when the earth and the sun are on opposite sides of Venus.

Make sure the Atlas Mode option on the Chart menu is selected. Click the [image] button on the Animation toolbar to set the date to June 15, 1999. It really doesn't matter what the time is, but you can set it to midnight if you like. Use the Zoom Level command on the View menu to set the zoom level to 8. Click the [image] button on the Search toolbar to move Venus to the center of the display.

You should now see Venus close to the Beehive star cluster in the constellation Cancer. Set the animation time step to one solar day by using the Time Step command on the Animation menu. Venus is currently locked to the center of the display -- a result of using the program's search feature -- so when you start animation it will remain at the center of the display. Click the [image] button on the Animation menu to start animation.

Watch Venus move across the sky. Venus will move from west to east across Cancer and Leo for about six weeks. It will slow down and halt its eastward motion soon after it passes the star Regulus at the end of July. The planet's normal west to east motion is referred to as direct or prograde motion. Venus will then move "backwards", from east to west, until it returns to Cancer. This east to west motion, which will take place until the middle of September, is referred to as retrograde motion. By the end of September Venus will resume prograde motion and will once again be moving through the constellation Leo.


Retrograde motion of a superior planet

While performing this exploration you'll observe the retrograde motion of the planet Mars.

Mars' orbit lies outside that of the earth, which is why Mars is referred to as a "superior" planet. With respect to the sun, the center of our solar system, Mars' orbit is "above" that of the earth. Planets that are closer to the sun move more quickly than planets that are farther away. The earth therefore moves more quickly along its orbit than Mars, and at some point the earth will catch up to and move past Mars. This happens when Mars is near opposition, that is, when the planet and the sun are on opposite sides of the earth.

Make sure the Atlas Mode option on the Chart menu is selected. Click the [image] button on the Animation toolbar to set the date to March 1, 1999. It really doesn't matter what the time is, but you can set it to midnight if you like. Use the Zoom Level command on the View menu to set the zoom level to 8. Click the [image] button on the Search toolbar to move Mars to the center of the display.

You should now see Mars in the constellation Libra, not far from the border with Virgo. Set the animation time step to one solar day by using the Time Step command on the Animation menu. Mars is currently locked to the center of the display -- a result of using the program's search feature -- so when you start animation it will remain at the center of the display. Click the [image] button on the Animation menu to start animation.

Watch Mars move across the sky. Mars will move from west to east across Libra for a couple of weeks but will then slow down and halt its eastward motion. The planet's normal west to east motion is referred to as direct or prograde motion. Mars will then move "backwards", from east to west, into the constellation Virgo. This east to west motion, which will take place throughout April and May, is referred to as retrograde motion. Mars will halt its retrograde motion when it gets near the star Spica at the beginning of June. Soon it will move quickly from west to east again and by the beginning of August the planet will be back in Libra.

To understand what you've just seen, imagine driving down a highway in a car and passing a slower car in another lane. Even though the other car is moving forward, it will appear to be moving backward in relation your car and the scenery outside. Similarly, when the earth overtakes and moves past Mars, the planet appears to move backward with respect to the background stars.


Using the online Help system

This Help file documents all of CyberSky's many features and also provides a good deal of reference information about constellations and solar system objects. If you're just getting interested in astronomy, the glossary of astronomical terms may also be very useful to you.

To view Help for toolbar buttons and menu commands

When you move the pointer over a toolbar button and wait a second you'll see the name of the button appear in a small ToolTip window. A short description of the button will also appear in the left part of the status bar. To view more detailed Help:

•	Click the [image] button on the View toolbar to turn the pointer into an arrow with a question mark, and then click the button or command.

•	Press the Shift+F1 keys, and then click the button or command.

Use the same procedures to view Help for other parts of CyberSky's window, such as the panes in the Data bar or Pointer bar.

To view Help for dialog boxes

When you are using a dialog box and would like to view Help:

•	Click the dialog box's Help button.

•	Press the F1 key.

Help for the dialog box will appear.


System requirements

System requirements for CyberSky 3.1 are as follows:

•	Personal computer with an Intel Pentium or compatible processor.

•	Microsoft Windows 95, 98, NT 4.0, or 2000 operating system.

•	About 5 MB of disk space for the registered version; about 2 MB for the shareware version.

•	Desktop area 800 by 600 pixels in size or larger.

•	Microsoft mouse or compatible pointing device.


Obtaining the latest version

Months or even years may have passed since this version of CyberSky was released. To find out if you're running the latest version of CyberSky, please check at www.cybersky.com.

Minor version updates (3.0.1, 3.0.2, and so on) will be made available to correct any problems that are discovered and to provide enhancements and modifications requested by customers. These releases will be distributed as patch files that will update the version installed on your computer to the latest version.

Major version upgrades (4.0, 5.0, and so on) will be made available for purchase at www.cybersky.com and will be offered to registered users at a discount.


Reporting a problem

If you encounter a problem while using CyberSky, or find an error in the program's documentation, please report your discovery to support@cybersky.com, or to Stephen Michael Schimpf, 2444 West 230th Street, Torrance, CA 90501-5242, USA. It is possible that the problem you've encountered has already been corrected. Please visit www.cybersky.com to find out if you're running the latest version of the software.

When reporting a problem, please be as descriptive as possible. Provide any relevant information about the hardware and software you are using, describe any messages you may have seen, and list the steps required to reproduce the problem. Be sure to mention which version of CyberSky and which version of Windows you are running. If the problem involves printing a sky chart, be sure to mention the make and model of printer you're using.


Submitting a suggestion

This latest version of CyberSky is the result of the many suggestions I've received from helpful customers all over the world. These suggestions let me know what features customers would like to see in future versions of CyberSky, and help me decide how to budget my limited programming time.

If you have a suggestion for a new feature or an enhancement of an existing feature, please submit your suggestion to stephen@cybersky.com, or to Stephen Michael Schimpf, 2444 West 230th Street, Torrance, CA 90501-5242, USA. Be assured that all comments and suggestions are recorded and will shape future versions of CyberSky.


Setting your location and time zone

The first time you start CyberSky, the program will display the sky as visible from Torrance, California, USA. Unless you happen to live in Torrance, you'll need to specify another location so that CyberSky can produce accurate sky charts for you. The sky seen in California looks very different from the sky seen in Australia! CyberSky knows the longitudes, latitudes, and time zones of well over a thousand locations around the world, and you can add more locations to the program's database if necessary.

Use the Location command on the Options menu to display the Location dialog box. To specify your location, click the down arrow in the Name box, scroll down until you find the location's name, and then click the name. If you can't find your location in the list, select the name of a nearby location. Click the Set As Home button to make the location your home location. This will allow you to change the location in the future, as many times as you like, and then quickly return to your home location by using the Return Home command on the Options menu. Click the OK button to close the dialog box and update the sky chart.

CyberSky can now use the longitude, latitude, and time zone of your location to produce accurate sky charts. Unfortunately, the use of daylight saving time effectively changes your time zone for about six months out of each year. For example, if your time zone is normally eight hours behind universal time, it is only seven hours behind when daylight saving time is in effect. Daylight saving time is adopted to prolong sunlight into evening hours. In the United States, daylight saving time is used from 2:00 AM on the first Sunday in April to 2:00 AM on the last Sunday in October. The states of Arizona and Hawaii, as well as some counties in the Midwest, do not observe daylight saving time.

Click the [image] button on the Animation toolbar to display the Local Time dialog box. Check the Daylight saving time option if daylight saving time is currently in effect. In the future, be sure to check or uncheck this option, if necessary, whenever you change the local time. Click the OK button to close the dialog box and update the sky chart.


Understanding the program's window

Whenever you run CyberSky, a small window -- known as a splash screen -- will appear for a few seconds to identify the name and number of the version you're running. CyberSky will then read the date and time from your computer's clock and will use this information to display the sky visible above the south horizon.

The main window

The program's main window will initially take up as much of the screen as possible, but will not cover the Windows taskbar. You can, of course, make the window smaller and move it around the screen at any time. Whenever you change the position and size of the main window, CyberSky will remember these new settings until you change them again. Similarly, CyberSky will remember the positions and sizes of the toolbars and other control bars described below. When you run CyberSky again, all of the program's windows will be displayed just like they were when you last exited the program.

The sky chart

CyberSky's simulated view of the sky fills most of the program's main window. Other Help topics describe the contents of the sky chart and the orientation of the cardinal directions in detail.

CyberSky includes a feature called full screen mode that let's you display a sky chart that takes up the entire screen. When full screen mode is turned on, all parts of the program's window except the sky chart will disappear, and the sky chart will expand to fill up the entire screen. When this happens you can still access the program's menus using the Alt key. For example, press the Alt+F keys to pull down the File menu, or the Alt+C keys to pull down the Chart menu. You can also use CyberSky's keyboard shortcuts to control the program.

Use the Full Screen command on the View menu or press the Ctrl+F keys to turn full screen mode on or off.

The toolbars

CyberSky's four toolbars give you easy access to many of the program's most frequently used features. Each of these toolbars contains buttons that perform related functions.

A toolbar can be docked along any edge of the sky chart. Here is the Animation toolbar in its initial position, docked along the top edge of the sky chart:

A toolbar can also be moved so that it floats above the sky chart. To turn a docked toolbar into a floating toolbar, move the pointer over the empty area around the toolbar's buttons, press and hold down the mouse button, and then drag the pointer away, toward the center of the sky chart. When the toolbar's outline has changed shape and is located where you want it, release the mouse button. Here is the Animation toolbar floating above the sky chart:

To turn a floating toolbar into a docked toolbar, move the pointer over the toolbar's title bar, press and hold down the mouse button, and then drag the pointer to any edge of the sky chart. When the toolbar's outline has changed shape and is located where you want it, release the mouse button.

You can also drag the edge of a floating toolbar to resize it. Here is the Animation toolbar once again, resized so that the toolbar buttons are arranged out in two rows:

When you move the pointer over a toolbar button and wait a second you'll see the name of the button appear in a small ToolTip window. A short description of the button will also appear in the left part of the status bar.

The View toolbar

The View toolbar contains buttons that deal with printing a sky chart, previewing a printed sky chart, changing the zoom level, displaying a standard horizon or zenith view, scrolling the sky chart, and obtaining context-sensitive Help.

Use the View Toolbar command on the View menu to display or hide the View toolbar.

The Animation toolbar

The Animation toolbar contains buttons that deal with changing the time, starting and stopping animation, and locking solar system objects to the center of the display.

Use the Animation Toolbar command on the View menu to display or hide the Animation toolbar.

The Chart toolbar

The Chart toolbar contains buttons that deal with displaying or hiding components of the sky chart.

Use the Chart Toolbar command on the View menu to display or hide the Chart toolbar.

The Search toolbar

The Search toolbar contains buttons that deal with searching for solar system objects. These buttons are labeled with the traditional astronomical symbols for the sun, moon, and planets.

Use the Search Toolbar command on the View menu to display or hide the Search toolbar.

The Data bar

The panes in the Data bar display the local and universal time and other information about the sky chart. Click a pane to access a dialog box or perform a related command. For example, click the pane that displays the local time to display the Local Time dialog box.

Use the Data Bar command on the View menu to display or hide the Data bar.

You can dock the Data bar along the left or right edge of the sky chart, using the same procedure described above for toolbars. But, you cannot dock the Data bar along the top or bottom edge. You can also turn the Data bar into a floating control bar, as shown above.

The Pointer bar

The panes in the Pointer bar display the equatorial coordinates, horizontal coordinates, and constellation under the mouse pointer. Click the equatorial or horizontal coordinates pane to turn the equatorial or horizontal coordinate system grid on or off, or the constellation pane to access the Constellations dialog box.

Use the Pointer Bar command on the View menu to display or hide the Pointer bar.

You can dock the Pointer bar along the left or right edge of the sky chart, using the same procedure described above for toolbars. But, you cannot dock the Pointer bar along the top or bottom edge. You can also turn the Pointer bar into a floating bar, as shown above.

The status bar

The status bar is displayed across the bottom of the sky chart. The left part of the status bar contains a description of the action performed by the menu command currently selected, or by the toolbar button currently under the pointer. The right part contains two panes that display the name and coordinates of the location from which you're viewing the sky.

The left part of the status bar also displays the angular separation between two points in the display. To measure an angular separation, move the pointer over the first point, click and hold down the left mouse button, drag the pointer to the second point, and then release the mouse button.

The angular separation between the two points will be displayed in the status bar until another message takes its place.

Use the Status Bar command on the View menu to display or hide the status bar. The status bar cannot be moved or turned into a floating bar.


Understanding the sky chart

CyberSky uses a variety of different colors and symbols to represent different types of celestial objects and to convey information about the sky. You may be unfamiliar with some of the symbols used, but with a little explanation you'll find the sky chart easy to understand.

The images displayed below show small areas of sky charts produced using CyberSky's default color scheme. If you prefer another color scheme, you can use the Colors command on the Options menu at any time to customize screen and printer colors to your liking.

The sky background

By default, the color of the sky background varies depending on the altitude of the sun.

The sky background is displayed like this during daytime, when the sun is above the horizon...

…and like this during civil twilight, when the sun is less than 6 degrees below the horizon...

…and like this during nautical twilight, when the sun is more than 6 but less than 12 degrees below the horizon...

…and like this during astronomical twilight, when the sun is more than 12 but less than 18 degrees below the horizon...

…and like this during nighttime, when the sun is more than 18 degrees below the horizon.

If you prefer, you can turn this feature off so that the sky background remains the same color regardless of the altitude of the sun. Use the Daylight command on the Options menu or press the Ctrl+D keys to turn daylight on or off.

The horizon

The thick orange line that curves along the bottom of the sky chart represents the horizon. This line is curved rather than straight due to the projection CyberSky uses to display the celestial sphere on the screen.

When the horizon is displayed, tick marks and labels indicate the positions of the cardinal points along the horizon: north ("N" at 0 degrees), northeast ("NE" at 45 degrees), east ("E" at 90 degrees), southeast ("SE" at 135 degrees), south ("S" at 180 degrees), southwest ("SW" at 225 degrees), west ("W" at 270 degrees), and northwest ("NW" at 315 degrees).

The horizon. The tick mark labeled "S" indicates the position of the south point on the horizon, located at 180 degrees azimuth.

Click the [image] button on the Chart toolbar, use the Horizon command on the Chart menu, or press the Ctrl+H keys to display or hide the horizon. Hiding the horizon will also hide the cardinal direction labels and will allow you to see the sky below the horizon.

You may notice celestial objects move when you turn the horizon on or off. When the horizon is displayed the positions of celestial bodies are adjusted to take into account the effect of atmospheric refraction. When you hide the horizon these adjustments are not performed, so the bodies shift back to the positions they would have if the earth's atmosphere didn't exist.

Stars

A star is a spherical, gaseous body that generates energy by nuclear fusion reactions in its core. These reactions, which convert hydrogen into helium and helium into heavier elements, allow a typical star to shine for billions of years.

If you take a look at stars in the sky you'll see that they're not all white. Many appear to have a pure white color, but many others appear to have a touch of blue in their light, while others appear to have a touch of yellow, or orange, or even red.

These colors you see are indications of the surface temperatures of these stars. The blue stars are the hottest, and the red stars are the coolest. Stars are classified into spectral classes, named O, B, A, F, G, K, and M, based on the characteristics of their light, which are in turn dependent on their surface temperatures.

Circular symbols of various sizes represent stars. Larger symbols represent brighter stars, and smaller symbols represent fainter ones. CyberSky initially displays stars to magnitude 4.5, about as many stars as you can see from an urban location. By default, this limiting magnitude will be increased or decreased automatically as you zoom in or out. You can disable this behavior if you wish.

Stars can be displayed in white only:

Stars displayed in white only.

Or, they can be displayed in colors based on their spectral types:

Stars displayed in colors.

Click the [image] button on the Chart toolbar to display or hide stars, and the [image] button on the same toolbar to display or hide star labels.

Use the Stars command on the Chart menu to set star display options.

Constellations

Constellations are arbitrary groupings of stars, invented to break the sky into smaller, more manageable pieces, thereby making it possible for the human mind to quickly identify the stars visible at a given time. Many constellations are very old, but in ancient times constellations had no fixed limits. A constellation consisted of a group of stars that defined a stick figure or outline resembling a mythological person, an animal, or a monster. It often takes a great deal of imagination to "see" these objects in the sky.

CyberSky can display simple stick figures connecting stars to represent the constellations. These figures are not sanctioned by any official body, and the ones displayed by CyberSky may differ significantly from those you see displayed in books and magazines. Different authors use different sets of figures, some perhaps more attractive and suggestive of the objects after which the constellations are named than others.

Figure of the constellation Gemini.

Click the [image] button on the Chart toolbar to display or hide constellation figures.

Although it is these constellation figures that come to mind whenever constellations are mentioned, the only official definitions of the constellations are their boundaries. Strictly speaking, constellations are simply areas of the sky. Just as any city on the earth falls within the boundaries of some state, province, or country, all celestial bodies fall within the boundaries of a constellation.

Boundary of the constellation Gemini.

Click the [image] button on the Chart toolbar to display or hide constellation boundaries.

Constellations can be labeled with their official Latin names, abbreviations, or English or German equivalents.

Click the [image] button on the Chart toolbar to display or hide constellation labels.

Use the Constellations command on the Chart menu to set constellation display options.

Deep sky objects

Deep sky objects, which include galaxies, globular clusters, various types of nebulae, and open clusters, are represented by the symbols used in traditional printed star atlases.

Galaxies are composed of hundreds of millions or even hundreds of billions of stars, and their diameters range from a few thousand to hundreds of thousands of light years. Many galaxies are flat disks that have a spiral appearance. Many others are elliptical and show no structural features. The rest are irregular in shape.

Globular clusters are large clusters of stars located outside our galaxy. They contain about 100,000 stars, and are therefore much larger than the open or galactic clusters found within our galaxy.

Nebulae are clouds of gas and dust. Many deep sky objects originally called nebulae are now known to be galaxies just like own.

Open clusters are small clusters of stars, containing a few hundred stars at most, located in the disk of our galaxy. Open clusters are also known as galactic clusters.

Click the [image] button on the Chart toolbar to display or hide deep sky objects, and the [image] button on the same toolbar to display or hide deep sky object labels.

Use the Deep Sky Objects command on the Chart menu to set deep sky object display options.

Solar system objects

The solar system consists primarily of the sun and nine planets: Mercury, Venus, the earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. The sun is a typical star, one of about 200 billion stars that make up the Milky Way galaxy. The solar system is located about 30,000 light years from the center of the Milky Way galaxy.

Solar system objects are displayed as disks. At low zoom levels these disks are all shown at the same size and are not drawn to correct scale. You can even see the phases of Mercury and Venus, something that is impossible without optical aid.

Venus at a low zoom level, near the star Regulus in Leo.

This way of showing solar system objects is certainly unrealistic, but it has the benefit of making these objects stand out and easy to spot in the display. In addition, being able to observe the phases of Mercury and Venus change as they move around the sun can be very educational.

At high zoom levels the disks of solar system objects are drawn to correct scale.

Venus at a high zoom level.

At high zoom levels the four Galilean satellites of Jupiter, named Io, Europa, Ganymede, and Callisto, become visible.

Jupiter and a few of its moons.

The Galilean satellites are displayed in green to make them stand apart from stars. It's a lot of fun to use CyberSky's animation feature to watch these moons move around Jupiter!

At high zoom levels the rings of Saturn also become visible.

Saturn and its beautiful ring system.

The orientation of the ring system changes over time and is accurately displayed by CyberSky. The rings of Saturn are seen edge on approximately every fifteen years as the earth passes through the plane of the system. The last time this happened was in February, 1996.

Click the [image] button on the Chart toolbar to display or hide solar system objects, and the [image] button on the same toolbar to display or hide solar system object labels.

Use the Solar System Objects command on the Chart menu to set solar system object display options.

Object paths

CyberSky can display the paths of solar system objects across the sky. The positions of objects along their paths can be marked and labeled with the date and time.

The path of Uranus. The positions of the planet are here shown marked and labeled at four-day intervals.

The path of a given solar system object is displayed in the same color used to display the object.

Use the Object Paths command on the Chart menu to display the paths of solar system objects across the sky.

The equatorial coordinate system grid

The equatorial coordinate system is equivalent to the system of longitude and latitude used on the surface of the earth. The coordinates are called right ascension and declination.

Right ascension is a measure of the angular distance of a point from the vernal equinox, measured eastward. Right ascension is usually given in hours rather than degrees, where one hour is equal to 15 degrees. Declination is a measure of the angular distance of a point from the celestial equator, measured northward.

The equatorial coordinate system appears fixed with respect to the stars, making it possible to specify coordinates that do not depend on the time of day or the viewing location.

The equatorial coordinate system grid. All intersections of grid lines are labeled with their right ascensions and declinations.

Click the [image] button on the Chart toolbar to display or hide the equatorial coordinate system grid.

The horizontal coordinate system grid

The horizontal coordinate system is also known as the altitude-azimuth system because the coordinates are called altitude and azimuth.

Azimuth is a measure of the angular distance of a point from the north point on the horizon, measured eastward. A point that is due north has an azimuth of 0 degrees, one that is due east has an azimuth of 90 degrees, and so on. Altitude is a measure of the angular distance of a point above the horizon.

The horizontal coordinate system appears fixed with respect to a given location on the earth's surface. But, the position of an object given in terms of altitude and azimuth is only valid for an instant because the object is moving across the sky with the motion of the celestial sphere.

The horizontal coordinate system grid. All intersections of grid lines are labeled with their azimuths and altitudes.

Click the [image] button on the Chart toolbar to display or hide the horizontal coordinate system grid.

The chart mode

The sky chart can be displayed in either atlas or horizon mode.

Atlas mode aligns the sky chart with the equatorial coordinate system. This is the orientation used in traditional printed star atlases. Lines of right ascension are generally vertical and lines of declination are generally horizontal. Sky charts printed using this mode are most useful if you're observing the sky using an equatorially-mounted telesope.

Horizon mode aligns the sky chart with the horizontal coordinate system. This is the orientation used in sky charts that show you what the sky will look like when you stand outside and look in a given direction. Lines of azimuth are generally vertical and lines of altitude are generally horizontal. Sky charts printed using this mode are most useful if you're observing the sky with your naked eyes, binoculars, or a telescope that is not equatorially-mounted, such as a Dobsonian.

If you don't understand any of this, don't worry about it for now. CyberSky uses horizon mode by default. After you've had a chance to use CyberSky for a while, switch between the two modes a few times and the difference should become obvious to you.

Use the Atlas Mode or Horizon Mode command on the Chart menu to select which mode you want to display.

The ecliptic

The ecliptic is the projection of the earth's orbital plane onto the celestial sphere. As the earth moves along its orbit during the course of a year, we look at the sun from different places in our orbit and therefore see the sun projected against different background stars. The sun moves roughly one degree along the ecliptic every day. You will always find the sun, moon, and planets on or near this line.

The ecliptic, with the sun and some planets visible.

The twelve constellations through which the sun moves are known as the constellations of the zodiac: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, and Pisces.

Click the [image] button on the Chart toolbar to display or hide the ecliptic.

When the ecliptic is displayed, a cross labeled "NEP" marks the position of the north ecliptic pole, and another one labeled "SEP" marks the position of the south ecliptic pole.

The celestial equator

The celestial equator is the projection of the earth's equator onto the celestial sphere. It divides the sky into a northern half and a southern half. Objects north of the celestial equator have a positive declination, and cannot be seen from the South Pole. Objects south of the celestial equator have a negative declination, and cannot be seen from the North Pole.

The celestial equator passing through Orion.

Click the [image] button on the Chart toolbar to display or hide the celestial equator.

When the celestial equator is displayed, a cross labeled "NCP" marks the position of the north celestial pole, and another one labeled "SCP" marks the position of the south celestial pole.

The galactic equator

Our galaxy is a collection of hundreds of billions of stars distributed in a thin disk. When we look in a direction perpendicular to the plane of this disk, we see relatively few stars. But, when we look in a direction parallel to the plane we see many more stars. This concentration of stars forms a band around the sky that has been called the Milky Way since ancient times.

The galactic equator is the projection of the plane of our galaxy's disk onto the celestial sphere. As you use CyberSky you'll notice a definite concentration of stars along this line. You'll also find that open clusters, which are located in the disk of our galaxy, are concentrated around this line.

The galactic equator passing through Sagittarius and Scorpius.

Click the [image] button on the Chart toolbar to display or hide the galactic equator.

When the galactic equator is displayed, a cross labeled "NGP" marks the position of the north galactic pole, and another one labeled "SGP" marks the position of the south galactic pole.


Understanding the chart's orientation

If you're familiar with charts of the earth's surface, but not with charts of the sky, it is easy to become confused by the orientation of cardinal directions in a sky chart. A little explanation and a few diagrams should help you understand how CyberSky's sky chart relates to the real sky.

Picture yourself standing in a field far away from buildings, mountains, and trees. Your view of the horizon is unobstructed, so you can see the entire dome of the sky. If you face the north horizon, the south horizon will be behind you. The east horizon will be to your right, and the west horizon will be to your left. The sun will rise to your right, pass overhead, and then set to your left. The following diagram illustrates this situation:

The cardinal directions north, east, south, and west are marked by dots labeled N, E, S, and W. The point directly above your head is called the zenith, and is marked by a dot labeled Z.

Now picture what happens when you turn around to face the south horizon. The north horizon will now be behind you, and east and west will trade places. The east horizon will now be to your left, and the west horizon will be to your right. The sun will now rise to your left, pass overhead, and then set to your right. The following diagram illustrates this new situation:

Imagine tilting your head up so that you're looking at a point halfway between the south point on the horizon and the zenith. You'll see the south horizon at the bottom of your field of view, and the zenith will be at the top. You'll see the eastern part of the sky to the left, and the western part of the sky to the right. The following diagram illustrates this situation:

Click the [image] button on the View toolbar or press the S key to tell CyberSky to show you this view of the sky. Doing so will set the viewing azimuth to 180 degrees (south), the altitude to 45 degrees (halfway between the horizon and the zenith), and the zoom level to 2X. A similar view centered on a point above the north, east, or west horizon can be obtained by clicking the [image], [image], or [image] button on the View toolbar, or by pressing the N, E, or W key.

Click the [image] button on the View toolbar or press the Page Up key to increase the zoom level to 4X. Repeat this action to increase the zoom level to 8X. Doing so will not change the direction in which you're viewing the sky, but will show you a smaller and smaller area of the sky. This is equivalent to using binoculars or a telescope to view the sky. The following diagram illustrates your new field of view:

Click the [image] button on the View toolbar or press the Page Down key as many times as necessary to return the zoom level to 2X. Or, simply click the [image] button on the View toolbar or press the S key to quickly return to the standard south horizon view.

You're still facing south, looking at a point halfway between the horizon and the zenith. Now imagine tilting your head back, farther and farther, until you're looking straight up at the zenith. Or, imagine lying down on the ground and looking straight up. The following diagram illustrates your field of view from this position:

Click the [image] button on the View toolbar or press the Z key to tell CyberSky to show you this view of the sky.

When you tell CyberSky to show you one of the horizon views, the program sets the viewing azimuth to 0 degrees (north), 90 degrees (east), 180 degrees (south), or 270 degrees (west), and the altitude to 45 degrees (halfway between the horizon and the zenith). When you tell CyberSky to show you a full sky view, the program sets the azimuth to 90 degrees (the zenith), but does not change the azimuth.

The reason that the south horizon is at the bottom of the previous diagram is that you had earlier used the [image] button to view the sky above the south horizon. How would you go about displaying a full sky view with the east horizon at the bottom of the display? First, click the [image] button or press the E key to view the sky above the east horizon. Then, click the [image] button or press the Z key to tell CyberSky to show you a full sky view. The following diagram illustrates the result:

As you can see, CyberSky is very flexible. You can even use the [image] button on the Chart toolbar or press the Ctrl+H keys to hide the horizon altogether. This lets you move your viewing direction to a point below the horizon and still see the sky, as if the earth wasn't there to block your view!


Changing the viewing direction and zoom level

CyberSky allows you to easily display standard horizon and full sky views, to move the viewpoint to another part of the sky, and to zoom in and out to see the sky at higher and lower levels of magnification.

To display a standard horizon view

•	Click the [image], [image], [image], or [image] button on the View toolbar.

•	Press the N, E, S, or W key.

•	Use the North, East, South, or West command on the View menu.

When one of these views is selected, the program sets the viewing azimuth to 0 degrees (north), 90 degrees (east), 180 degrees (south), or 270 degrees (west), and the altitude to 45 degrees (halfway between the horizon and the zenith). The zoom level is set to 2X.

To display a full sky view

•	Click the [image] button on the View toolbar.

•	Press the Z key.

•	Use the Zenith command on the View menu.

When this view is selected, the program sets the viewing azimuth to 90 degrees (the zenith), but does not change the azimuth. The zoom level is set to 1X.

To move the viewpoint

•	Click the [image], [image], [image], or [image] button on the View toolbar. When the sky chart is displayed in atlas mode, scrolling occurs in right ascension and declination. When the sky chart is displayed in horizon mode, scrolling occurs in azimuth and altitude.

•	Press the left- or right-arrow key to scroll in right ascension or azimuth, or the up- or down-arrow key to scroll in declination or altitude. Use a Ctrl key along with an arrow key to scroll in smaller steps.

•	Right-click a point that you'd like to move to the center of the sky chart and then select the Center command on the popup menu that appears. Or, simply double-click the point.

You can also move the viewpoint by using the commands on the Search menu or the buttons on the Search toolbar.

To zoom in or out

•	Click the [image] or [image] button on the View toolbar.

•	Press the PgUp or PgDn key.

•	Use the Zoom In or Zoom Out command on the View menu.

•	Right-click the sky chart and use the Zoom In or Zoom Out command on the popup menu that appears.

•	Use the Zoom Level command on the View menu to set the zoom level to a desired value.

•	Use the 1 through 0 keys to set the zoom level to 1X through 512X.

•	Use the mouse wheel to zoom in or out if you have a Microsoft IntelliMouse or similar mouse with a wheel.

Zooming in or out causes the zoom level to increase or decrease by a factor of two. CyberSky allows you to view the sky at zoom levels between 1X and 8192X.


Using keyboard shortcuts

You can use keyboard shortcuts in place of the mouse for many operations. Keyboard shortcuts provide an excellent alternative to using the mouse when the program is in full screen mode. The following table lists all keyboard shortcuts:

Press	To

Ctrl+B	Save a sky chart as a bitmap file.

Ctrl+P	Print a sky chart.

Alt+F4	Close the application's window and exit the application.

PgUp	Display the sky chart at a higher zoom level.

PgDn	Display the sky chart at a lower zoom level.

1	Set the zoom level to 1X.

2	Set the zoom level to 2X.

3	Set the zoom level to 4X.

4	Set the zoom level to 8X.

5	Set the zoom level to 16X.

6	Set the zoom level to 32X.

7	Set the zoom level to 64X.

8	Set the zoom level to 128X.

9	Set the zoom level to 256X.

0	Set the zoom level to 512X.

N	Display the sky as seen when looking above the north horizon.

E	Display the sky as seen when looking above the east horizon.

S	Display the sky as seen when looking above the south horizon.

W	Display the sky as seen when looking above the west horizon.

Z	Display the sky as seen when looking toward the zenith.

Ctrl+F	Turn full screen mode on or off.

Left Arrow	Scroll the sky chart to the left.

Ctrl+Left Arrow	Scroll the sky chart to the left in smaller steps.

Right Arrow	Scroll the sky chart to the right.

Ctrl+Right Arrow	Scroll the sky chart to the right in smaller steps.

Up Arrow	Scroll the sky chart up.

Ctrl+Up Arrow	Scroll the sky chart up in smaller steps.

Down Arrow	Scroll the sky chart down.

Ctrl+Down Arrow	Scroll the sky chart down in smaller steps.

Ctrl+Home	Set the location to your home location.

Ctrl+D	Turn daylight on or off.

Ctrl+A	Turn atlas mode on.

Ctrl+Z	Turn horizon mode on.

Ctrl+H	Display or hide the horizon.

Ctrl+L	Set the local time at which the sky is being viewed.

Ctrl+U	Set the universal time at which the sky is being viewed.

Ctrl+J	Set the Julian date at which the sky is being viewed.

Ctrl+C	Set the local time to your computer's system time.

Ctrl+M	Set the local time to midnight.

Ctrl+R	Set the local time to sunrise.

Ctrl+N	Set the local time to noon.

Ctrl+S	Set the local time to sunset.

Ctrl+E	Set the local time to that of a rising, transit, or setting event.

<	Start animation with time moving backward.

[	Display the previous animation step.

Esc	Stop animation.

]	Display the next animation step.

>	Start animation with time moving forward.

Ctrl+T	Set the animation time step.

Ctrl+K	Lock or unlock a selected solar system object.

F1	Display the application's Help topics or context-sensitive Help.

Shift+F1	Display Help for menu commands, toolbar buttons, and window areas.


Glossary of astronomical terms

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A

aberration

absolute magnitude

absolute zero

albedo

almanac

altitude

analemma

Angstrom

angular diameter

angular measure

annular eclipse

aphelion

apogee

apparent magnitude

apparent solar time

apse

asterism

asteroid

asteroid belt

astrology

astrometry

astronomical twilight

astronomical unit

astronomy

astrophysics

atmosphere

atmospheric refraction

aurora

autumnal equinox

axial inclination

axis

azimuth

B

Bayer letter

binary star

black hole

bollide

C

caldera

cardinal points

celestial equator

celestial mechanics

celestial meridian

celestial poles

celestial sphere

Celsius scale

chromosphere

circumpolar

civil twilight

color index

coma

comet

conjunction

constellation

core

corona

cosmic rays

cosmogeny

cosmology

cosmos

crater

crescent

cusps

D

dark cloud

dark nebula

daylight saving time

declination

deep sky objects

density

diffuse nebula

direct motion

disk

distance

diurnal motion

double star

dwarf

E

east point

eccentricity

eclipse

ecliptic

ecliptic coordinate system

ecliptic latitude

ecliptic longitude

ellipse

elliptical galaxy

elongation

emission nebula

ephemeris

epoch

equation of time

equatorial coordinate system

equinox

escape velocity

evening star

F

Fahrenheit scale

fireball

first quarter

Flamsteed number

full

G

galactic cluster

galactic coordinate system

galactic equator

galactic latitude

galactic longitude

galaxy

Galilean satellites

gegenschein

geocentric coordinates

giant

gibbous

globular cluster

great circle

Gregorian calendar

H

harvest moon

horizon

horizontal coordinate system

hour angle

hour circle

hunter's moon

I

illumination

inclination

inferior conjunction

inferior planet

inner planet

intergalactic

interplanetary

interstellar

irregular galaxy

J

Julian calendar

Julian date

K

Kelvin scale

L

last quarter

latitude

light year

limb

local sidereal time

longitude

luminosity

luminosity classes

lunar eclipse

M

magnitude

main sequence

mantle

mare

mass

mean solar time

meridian

Messier catalog

meteor

meteoroid

meteorite

meteoritics

meteor shower

Milky Way

minor planet

moon

morning star

N

nadir

nautical twilight

nebula

neutron star

new

New General Catalogue

node

north point

North Star

nova

nuclear fusion

O

occultation

open cluster

opposition

orbit

orbital inclination

outer planet

P

parallax

parsec

partial eclipse

penumbra

perigee

perihelion

photosphere

planet

planetarium

planetary nebula

pole star

precession

prograde motion

prominence

proper motion

proper name

pulsar

Q

quadrature

quasar

R

radiant

radiation

reflection nebula

retrograde motion

revolution

right ascension

rotation

S

satellite

semi-major axis

sidereal day

sidereal time

solar day

solar eclipse

solar system

solar time

solstice

south point

spectral sequence

spectral types

spectrum

spiral galaxy

star

summer solstice

Summer Triangle

sun

sunspot

sunspot cycle

supergiant

superior conjunction

superior planet

supernova

supernova remnant

synodic period

T

terminator

topocentric coordinates

total eclipse

transit

tropical year

U

umbra

universal time

universe

V

variable star

vernal equinox

vertical circle

W

wane

Water Jar

wavelength

wax

west point

white dwarf

winter solstice

Winter Triangle

Y

year

Z

zenith

zodiac

zodiacal constellation

zodiacal light


aberration

A small shift in the position of a celestial object caused by the motion of the earth around the sun. The effect is small, measuring at most 20 arc seconds. Aberration was discovered by the English astronomer James Bradley in 1729 and was used by him to prove that the earth moves through space.


absolute magnitude (M)

The magnitude a celestial object would have if it were located at a standard distance of 10 parsecs or 32.6 light years from an observer. An object's apparent magnitude tells us how bright the object appears to an observer here on the earth, but we don't know how bright an object really is unless we take into account its distance from us.

The sun's absolute magnitude is about 4.8, meaning that if it were placed 10 parsecs away it would appear as an inconspicuous star in our sky. In contrast, if the star Rigel (β Orionis) were placed 10 parsecs away it would shine at magnitude -8, about as bright as a quarter moon!


absolute zero

A temperature of 0 Kelvin, -273 Celsius, or -460 Fahrenheit, at which all molecular motion stops.


albedo

A measure of the reflecting power of the surface of a non-luminous body such as a planet, moon, or asteroid. An albedo of 1.0 represents a white surface that reflects all light that strikes it whereas an albedo of 0.0 represents a black surface that absorbs all light that strikes it.

The surfaces of the planet Mercury and the moon are made mostly of volcanic rock that is a poor reflector of incident light. The albedos of Mercury and the moon are 0.07 and 0.06 respectively.

The surface of the earth consists largely of water and the earth's albedo is therefore higher, about 0.36.

The planet Venus as well as the giant gas planets Jupiter, Saturn, Uranus, and Neptune are shrouded in clouds that are good reflectors of light, and these bodies all have albedos above 0.5.


almanac

A table listing the position of a celestial body at various times. Also called an ephemeris.


altitude (h)

The angular distance of a celestial object above or below the horizon. Altitude and azimuth are coordinates in the horizontal coordinate system.

Altitude is usually measured in units of degrees from 0 degrees to 90 degrees for altitudes above the horizon and from 0 degrees to -90 degrees for altitudes below the horizon.

The apparent altitude of a celestial object is affected by atmospheric refraction. At the horizon atmospheric refraction adds more than half a degree to an object's altitude. This means that when you see the sun on the horizon it is actually below the horizon but you are able to see it because its light is refracted by the atmosphere.


analemma

A figure-eight pattern with one loop larger than the other, depicting the sun's declination and the equation of time over the course of one year.


Angstrom (A)

A unit of length used in measuring the wavelength of light and other electromagnetic radiation. One Angstrom is equal to one ten-billionth of one meter, or about the diameter of one hydrogen atom. A human hair is about 500,000 A in diameter.


angular diameter

The observed diameter of a celestial body, usually measured in degrees, minutes, and seconds of arc.


angular measure

Angles are measured in degrees (°), minutes ('), and seconds (") of arc. A full circle contains 360 degrees, a degree contains 60 arc minutes, and one arc minute contains 60 arc seconds.

The diameters of the sun and moon are about half a degree or about 30 arc minutes across.

One arc minute is about the smallest angular measure that can be perceived by the best human eyes without optical aid. One arc second is roughly the angular measure of a typical coin seen from five kilometers or three miles away.


annular eclipse

An eclipse of the sun in which the angular diameter of the moon's disk is not large enough to completely hide the sun's disk.


aphelion

The point in an object's orbit around the sun at which it reaches its greatest distance from the sun. The earth is at aphelion in early January.


apogee

The point in an object's orbit around the earth at which it reaches its greatest distance from the earth.


apparent magnitude (m)

The brightness of a celestial object, on the magnitude scale, as measured by an observer on the earth.

The apparent magnitude of a celestial object depends on its luminosity, its distance from the earth, and on the amount of light absorbed between the object and the earth.


apparent solar time

Time measured with respect to the apparent sun. Sundials display time based on the apparent sun.

The earth's orbit around the sun is not a perfect circle but is an ellipse. The earth does not move along this ellipse at constant speed, but moves fastest when it is closest to the sun and slowest when it is farthest from the sun. The apparent sun therefore moves along the ecliptic at a non-uniform rate.

The non-uniform motion of the apparent sun implies that the length of the solar day is dependent on the position of the earth in its orbit. This situation is not desirable for civil timekeeping. Ideally we want to be able to treat each day as if it was exactly 24 hours long. The mean sun, which moves along the celestial equator at a uniform rate, was invented with this goal in mind.


apse (plural: apsides)

The point in an orbit closest to or farthest from the center of gravitational attraction. The closest point is called the periapsis and the farthest point is called the apoapsis. In the case of the moon's orbit around the earth, the closest point is called the perigee, and the farthest point is called the apogee. In the case of a planet's orbit around the sun, the closest point is called the perihelion, and the farthest point is called the aphelion.


asterism

A distinctive group of stars that are not one of the 88 constellations recognized by the International Astronomical Union.

One example is the Big Digger, which is not itself a constellation but is part of the constellation Ursa Major. The Big Dipper is known as the Plough in Great Britain, and as the Wagon in Germany.

Another example is the Summer Triangle, made up of the brightest stars in the constellations Aquila, Cygnus, and Lyra, named Altair, Deneb, and Vega.


asteroid

One of many small, rocky bodies that orbit the sun. Asteroids are larger than meteoroids, but smaller than planets. Most are found between the orbits of Mars and Jupiter, but some cross the earth's orbit and have the potential to strike our planet at some point in the future.

Asteroids are also known as minor planets.


asteroid belt

A region of asteroids found between the orbits of the planets Mars and Jupiter.


astrology

A pseudo-science that claims to link the apparent and relative positions of the sun, moon, and planets in the sky to human personalities and destinies. There is no scientific basis to astrology.


astrometry

The branch of astronomy concerned with the measurement of the precise positions, sizes, and motions of stars and other celestial bodies.


astronomical twilight

The period between the time the sun is 12 degrees and 18 degrees below the horizon.


astronomical unit (AU)

A unit of length equal to the average distance between the earth and the sun. One AU is equal to 149,597,870 kilometers or 92,955,807 miles. One AU is a long way. A typical commercial airliner would take approximately 17 years to fly from the earth to the sun. Yet, the sun is the closest star.

The astronomical unit is mainly used for distances within the solar system. Pluto, the planet most distant from the sun, lies approximately 40 AU from the center of the solar system. The entire solar system is therefore about 80 AU in diameter. The nearest star outside the solar system is about 270,000 AU from the sun, or about 7,000 times the distance of Pluto!


astronomy

The science concerned with the study of the stars and all other bodies in the universe, the space between those bodies, and of the universe as a whole. Major branches of astronomy include astrometry, astrophysics, and celestial mechanics.


astrophysics

The branch of astronomy concerned with the study of the physical and chemical processes associated with celestial bodies and with the space between those bodies. Astrophysics focuses in particular on the production and expenditure of energy in stars and galaxies and seeks to understand how this activity affects the evolution of such systems.


atmosphere

The gaseous outer region of a star, planet, moon, or any other celestial body.

A celestial body can maintain an atmosphere if its escape velocity is sufficiently high. If this condition is not met, the gas molecules can escape into space and over time the body will loose its atmosphere.

If the temperature is too hot the lighter gas molecules will travel faster than the planet's escape velocity and will escape into space. If the temperature is too cold the gas molecules will freeze onto the surface of the planet, which may be the case on the planet Pluto.


atmospheric refraction

The bending of the light from a celestial object as it passes through the earth's atmosphere. Atmospheric refraction bends the light toward the earth, causing celestial objects to appear slightly higher in the sky than they really are.

The effect of atmospheric refraction depends on the altitude of the object and is greatest near the horizon. The position of an object at the horizon has been shifted by about 35 arc minutes toward the zenith, meaning that the object is really 35 arc minutes below the horizon but is visible due to atmospheric refraction.


aurora

A glowing, often moving, display of colored light seen high in the atmosphere near the north and south magnetic poles of the earth. Auroras are caused by charged particles from the sun that become trapped in the earth's magnetic field. High-altitude air molecules within about 20 degrees of the magnetic poles and approximately 100 kilometers or 60 miles high are excited by these particles and emit light.

An aurora in the Northern Hemisphere is called an aurora borealis, or the "Northern Lights". A similar effect in the Southern Hemisphere is called the aurora australis.


autumnal equinox

The time when the sun crosses the celestial equator moving from north to south. This takes places around September 23 and marks the beginning of fall in the northern hemisphere and the beginning of spring in the southern hemisphere.


axial inclination

The angle between a body's axis of rotation and the plane of its orbit.


axis

The line about which a body rotates, or about which a property such as its magnetic field is symmetrical. These two lines do not have to coincide. For example, the axis of the earth's magnetic field is tilted about 11.4 degrees with respect to its axis of rotation. A compass points to the magnetic north pole, not to the earth's geographic North Pole!


azimuth (A)

The angular distance from the north point measured eastward to the intersection of the horizon and the object's vertical circle. Altitude and azimuth are coordinates in the horizontal coordinate system.

Azimuth is usually measured in units of degrees from 0 degrees to 360 degrees.

Azimuth is also called compass bearing.


Bayer letter

A lower case letter of the Greek alphabet assigned to a star.

This system of star names was introduced by Johann Bayer in 1603 in the first true star atlas, his Uranometria, which catalogs 1277 stars. He assigned the letter α (alpha) to the brightest star in a constellation, β (beta) to the second-brightest star, γ (gamma) to the third brightest, and so on.

The letters are usually assigned in this order of brightness, but mistakes were made, so sometimes the star designated β is brighter than the star designated α.


binary star

A pair of stars that are revolving around a common center of gravity. Some components of binary stars are so close to each other that they complete one revolution in a fraction of a day. Others are so far apart that centuries pass before they complete one revolution.

The first such star was discovered by William Herschel (1738-1822), who proved the mutual revolution of Castor in 1803.

Binary and multiple stars are common in our galaxy. Perhaps about half of all stars are part of binary and multiple star systems. Binary stars are important to astronomers because observations of their orbital motions provides the only direct way to determine the masses of stars.


black hole

A collapsed star whose gravitational field has become so strong that not even light can escape it. A black hole cannot be observed directly, but its effect on its environment can be studied.


bollide

A term used for a very bright meteor that explodes into fragments near the end of its path through the earth's atmosphere.


caldera

The "crater" at the top of a volcano.


cardinal points

The four principal points on the horizon, called the north point (0 degrees azimuth), south point (180 degrees azimuth), east point (90 degrees azimuth), and west point (270 degrees azimuth).


celestial equator

A great circle formed by projecting the earth's equatorial plane onto the celestial sphere. The celestial equator is 90 degrees from both the north and south celestial poles.

The axis of the earth's daily rotation is tilted with respect to its orbital plane, and therefore the ecliptic and celestial equator are tilted with respect to each other. This angle, known as the obliquity of the ecliptic, is currently roughly 23.5 degrees. The precession of the earth's axis causes this angle to slowly change over time.


celestial mechanics

The branch of astronomy concerned with the study of the motions of celestial bodies under the influence of the force of gravity.


celestial meridian

The projection of the observer's meridian on the celestial sphere. The observer's celestial meridian passes through both celestial poles, and passes through the observer's zenith.

The celestial meridian divides the sky into an eastern half and a western half. When an object in the sky is in the east half, it is rising, and when it is in the west half it is setting. When the object is on the celestial meridian, it has reached its highest point in the sky.

You probably expect the sun to cross the meridian at noon, but this is generally not the case. The reasons for this are that the location from which you are viewing the sky is probably not located in the center of its time zone, the effect called the equation of time, and the adoption of daylight saving time.


celestial poles

The projections of the North and South poles of the earth's axis of rotation onto the celestial sphere. The precession of the earth's axis causes the celestial poles to trace out circles on the celestial sphere in a period of about 25,800 years.

The north celestial pole is currently found near the star Polaris, better known as the North Star, or more formally as α Ursae Minoris. The south celestial pole is currently found in the constellation Octans.


celestial sphere

When discussing the appearance and motion of the sky, it is useful to imagine that the sky is a great, hollow sphere surrounding the earth, and that the celestial bodies we see are somehow attached to the inner surface of this sphere. This imaginary sphere, called the celestial sphere, appears to rotate around the earth from east to west, although we know it is really the earth that is moving from west to east.

The point directly above you is called the zenith. The line that passes the north point on the horizon, the zenith, and the south point on the horizon is called the meridian.

The points on the celestial sphere directly above and below the earth's North and South poles are called the north and south celestial poles. As the celestial sphere rotates from east to west everything in the sky appears to rotate around these two points.

Halfway between the celestial poles is found a great circle known as the celestial equator. The celestial equator is the projection of the earth's equator onto the celestial sphere. It divides the sky into a northern half and a southern half.

As the earth turns on its axis the sky appears to turn in the opposite direction. Over time the sky will turn from east to west and the stars, sun, moon, and planets will appear to rise in the east, move across the sky, and set in the west.


Celsius scale (C)

A temperature scale that sets the freezing point of water at 0 degrees and the boiling point of water at 100 degrees. Because there are 100 divisions between the freezing and boiling points of water, the size of a degree in the Celsius scale is larger than the size of a degree in the Fahrenheit scale which has 180 divisions.

The Celsius scale was invented in 1742 by Swedish astronomer Anders Celsius (1701-1744).


chromosphere

The layer of the sun's atmosphere just above the photosphere, and just below the corona.


circumpolar

A term used to describe stars that are permanently above the horizon at a given location on the earth. All stars with positive declinations are circumpolar at the North Pole, and all stars with negative declinations are circumpolar at the South Pole.


civil twilight

The period between the time of sunrise or sunset and the time the sun is 6 degrees below the horizon.


color index

The difference between the apparent magnitude of a star measured at one standard wavelength of light and another longer wavelength. A star's color index value depends on the distribution of light across the spectrum, and is therefore a measure of the color and temperatures of the star.

Colors indices are currently measured using the Johnson-Morgan UBV system. The apparent magnitude of a star is measured at three wavelengths, ultraviolet (U) at 3600 Angstroms, blue (B) at 4200 Angstroms, and greenish-yellow (V) at 5400 Angstroms. Subtracting these values yields the U - B and B - V color indices. The more positive the color index, the redder and cooler the star is. The more negative the color index, the bluer and hotter the star is.


coma

The bright diffuse halo of a comet.


comet

A diffuse body of gas and solid particles that orbits the sun in an orbit generally more elliptical than that of planets. Most orbit the sun in very elongated orbits and appear at regular intervals. Others appear only once and then disappear into interstellar space, never to return.

Comets typically consist of three parts. The nucleus is usually about one mile across and is thought to resemble a dirty snowball. The coma surrounds the nucleus. The tail consists of gas and dust and appears only when the comet nears the sun. A comet's tail always points away from the sun.


conjunction

The moment when a planet's elongation is 0 degrees.


constellation

Constellations are arbitrary groupings of stars, invented to break the sky into smaller, more manageable pieces, thereby making it possible for the human mind to quickly identify the stars visible at a given time. Easy identification of stars was important to ancient sailors, because stars played a key role in navigation.

Many constellations are very old, but in ancient times constellations had no fixed limits. A constellation consisted of a group of stars that defined a stick figure or outline resembling a mythological person, an animal, or a monster. The Greek astronomer Ptolemy listed only 48 constellations. The names of these ancient Greek constellations were eventually Latinized, and it is by these Latin names that we know these constellations today. In more recent times more constellations were added for the areas of the southern sky that became visible to European explorers.

It became necessary to standardize the constellations and define precise boundaries separating all constellations. Just as any city on the earth falls within the boundaries of some state, province, or country, all celestial bodies fall within the boundaries of a constellation. The International Astronomical Union established the boundaries of 88 constellations in 1930. The constellation boundaries follow arcs of right ascension and declination for the epoch of January 1, 1875.

The stars in a given constellation usually have no connection to each other, but merely lie in the same direction as viewed from the earth. Some of the stars in a constellation are relatively near the solar system, and others are tens or hundreds of times farther away. Seen from another direction, our constellations would be unrecognizable, because the stars we recognize as making up the constellations would change both their brightness and their positions. If human beings one day establish a colony on a planet orbiting another star, they will need to invent a new set of constellations.

Although the stars found in a given constellation do move across space, their apparent motion is so slow that it doesn't affect the appearance of a constellation over a human lifetime, or in fact many human lifetimes. The constellations we see in our sky today appeared the same to people who lived hundreds or thousands of years ago. But, if we were to travel 25,000 or 50,000 years into the past or into the future, we would find that many of our constellations would look distorted, or in some cases would be unrecognizable.


core

The central region of a star, planet, moon, or any other celestial body.


corona

The outer atmosphere of the sun, only visible at the time of a total solar eclipse. The sun's corona has a temperature of about 2 million K.


cosmic rays

Highly energetic particles from interstellar space, moving at close to the speed of light, that bombard the earth from all directions.

Cosmic rays were discovered by VF Hess during a balloon flight in 1912.


cosmogeny

The study of the origin and evolution of the universe or one of its components, such as galaxies or the solar system.


cosmology

The study of the structure and evolution of the universe.


cosmos

Everything there is. Another term for universe.


crater

A circular depression observed on the surface of a terrestrial planet or a moon. Craters are formed when a large meteoroid or asteroid strikes the surface of the object.

Craters formed on bodies that don't posses an atmosphere, such as Mercury or the moon, are not subject to erosion and therefore appear as they did when they were formed. Craters formed on bodies that possess an atmosphere, such as the earth or Mars, show signs of erosion due to rain and wind.


crescent

A term used to describe the appearance of a planet or moon when between zero and 50 percent of the its disk is illuminated by sunlight. In other words, when the phase of the planet or moon is between new and first quarter, or between last quarter and new.


cusps

The pointed ends of the illuminated portion of Mercury, Venus, or the moon at crescent phase.


dark cloud

An interstellar cloud of gas and dust that is dense enough to block the passage of light.


dark nebula

An interstellar cloud of gas and dust that is dense enough to block the passage of light.


daylight saving time (DST)

Daylight saving time is adopted in some areas for spring and summer use to prolong sunlight into evening hours. One hour is added to standard time to obtain daylight saving time.

In the United States, daylight saving time is currently in effect from 2:00 AM on the first Sunday in April to 2:00 AM on the last Sunday in October. The states of Arizona and Hawaii, as well as some counties in the Midwest, do not make use of daylight saving time.


declination (Decl, Dec, or δ)

The angular distance of a celestial object north or south of the celestial equator. Right ascension and declination are coordinates in the equatorial coordinate system.

Declination is analogous to latitude on the earth's surface. Declination is usually measured in units of degrees, minutes, and seconds from -90 degrees to 90 degrees.


deep sky objects

Deep sky objects are objects such as galaxies, nebulae, and star clusters. With only a handful of exceptions, deep sky objects are not visible without optical aid such as binoculars or a small telescope.

Deep sky objects appear fainter than their magnitude values would indicate. Unlike a star, whose light appears to be concentrated in a point, a deep sky object appears spread out over a relatively large area. Deep sky objects are therefore said to have a low surface brightness and are often hard to see.

Some deep sky objects have popular names associated with them, and most have been assigned catalog numbers. CyberSky can label deep sky objects with their popular names (for example, "Orion Nebula"), their Messier catalog numbers ("M 42"), or other catalog numbers ("NGC 1976").


density (ρ)

The amount of mass per unit volume, usually measured in grams per cubic centimeter. The density of water is 1.0 gram per cubic centimeter. Objects with a density greater than that of water will sink in water, whereas those with a density less than that of water will float on water.

The density of iron is 7.9 grams per cubic centimeter, and the density of lead is 11.3 grams per cubic centimeter.


diffuse nebula

A cloud of gas and dust in interstellar space, measuring on average twenty light years across. Diffuse nebulae consist mostly of hydrogen, helium, nitrogen, and oxygen.

Such clouds of gas and dust are invisible unless illuminated by the light of nearby stars. If one or more nearby stars are very hot, their intense ultraviolet radiation will cause the nebula to emit light by the process of fluorescence, causing it to glow brightly. If all nearby stars are cool the nebula will appear less bright as it will merely reflect their light.


direct motion

The apparent west to east motion of a planet as seen from the earth against the background of distant stars. Direct motion is also described as prograde motion.


disk

The visible surface of a celestial body.


distance

The physical separation between two celestial objects. CyberSky displays the distance of the earth's moon in kilometers and miles, and the distances of other solar system objects in astronomical units.

By simply looking up at the stars you have no way of knowing how near or how far away any of them are. It is natural to assume that a bright star must be nearby whereas a faint star must be much further away, but this is not necessarily the case.

For example, take a look at Procyon and Betelgeuse, two bright stars in the constellations Canis Minor and Orion, respectively. Procyon is only slightly brighter than Betelgeuse. Yet, it turns out that Procyon is about 3.5 parsecs (11.3 light years) from us and Betelgeuse is about 200 parsecs (650 light years) from us. Imagine how bright Betelgeuse must be to shine as bright as Procyon even though it is so much farther away. Betelgeuse is in fact about 1,700 times as bright as Procyon.

A star's distance from us not only affects how bright it will appear to us, but also how far back in time we are looking when we see it. Stars are so far away from us that it takes their light years to reach us. In the case of Betelgeuse, you are seeing the star as it was 650 years ago.


diurnal motion

The apparent daily east to west motion of celestial bodies and of the sky as a whole, caused by the west to east rotation of the earth on its axis.


double star

A pair of stars that appear close together in the sky. Such stars may be physically close to each other and revolve around a common center of gravity, in which case they are called binary stars. Or, such stars may simply lie in the same direction in space and be otherwise unrelated to each other.


dwarf

A term used to describe a typical star such as the sun that is generating energy by converting hydrogen into helium. Stars spend most of their lifetime in the "dwarf" or "main sequence" stage of stellar evolution.


east point

The point on the horizon at 90 degrees azimuth.


eccentricity (e)

A measure of the degree of flattening of an ellipse. An ellipse with zero eccentricity is called a circle.

Most of the planets and moons in the solar system have orbits with eccentricities under 0.25. Venus has the least eccentric orbit. Its orbit is almost a circle. Pluto has the most eccentric orbit. The orbits of most comets are much more eccentric.


eclipse

A total or partial obscuration of light from a celestial body as it passes through the shadow of another body. Note that a solar eclipse is really an occultation.

Each year at least two and no more than five solar eclipses occur.


ecliptic

The plane of the earth's orbit, and the projection of that plane onto the celestial sphere. It is the line in the sky along which the sun appears to move during the course of a year. The sun moves roughly one degree along this line every day.

Because the orbits of the naked-eye planets have inclinations of seven degrees or less with respect to the ecliptic, you will always find these planets on or very close to this line.


ecliptic coordinate system

The coordinate system in which the fundamental reference circle is the ecliptic and the zero point is the vernal equinox. The coordinates are named ecliptic longitude (λ) and ecliptic latitude (β).


ecliptic latitude (β)

The angular distance of a celestial object above or below the ecliptic. Ecliptic longitude and ecliptic latitude are coordinates in the ecliptic coordinate system.

Ecliptic latitude is usually measured in units of degrees, minutes, and seconds of arc from 0 degrees to 90 degrees for latitudes above the ecliptic, and from 0 degrees to -90 degrees for latitudes below the ecliptic.


ecliptic longitude (λ)

The angular distance of a celestial object east of the vernal equinox. Ecliptic longitude and ecliptic latitude are coordinates in the ecliptic coordinate system.

Ecliptic longitude is usually measured in units of degrees, minutes, and seconds of arc from 0 degrees to 360 degrees.


ellipse

A geometric curve in the shape of a "squashed" circle. The exact shape of an ellipse is determined by a value known as its eccentricity.


elliptical galaxy (E)

A galaxy that has elliptical contours and that contains no conspicuous interstellar material.

Elliptical galaxies are classified according to their apparent degree of oblateness. Perfectly round elliptical galaxies are classified as type E0, and elongated, lens-shaped elliptical galaxies are classified as type E7.


elongation

The angular distance between the sun and a planet or moon.

An object with an east elongation appears east of the sun in the evening sky, and an object with a west elongation appears west of the sun in the morning sky. An elongation of 0 degrees is called a conjunction; one of 90 degrees is called quadrature; and one of 180 degrees is called opposition.

The greatest possible elongation for Mercury is about 28 degrees and for Venus about 48 degrees.


emission nebula

A type of diffuse nebula that is caused to radiate visible light by the absorption of ultraviolet light of a nearby star.


ephemeris

A table of calculated positions of a celestial body or celestial bodies over successive intervals of time.


epoch

A point of time selected as a fixed reference, especially for stellar positions or orbital elements.


equation of time

The difference between time based on the apparent sun and the mean sun. In other words, the difference between time as reported by a sundial and a clock.

The apparent sun runs up to 16 minutes fast with respect to the mean sun, and up to 14 minutes slow.


equatorial coordinate system

A coordinate system in which the fundamental reference circle is the celestial equator and the zero point is the vernal equinox. The coordinates are named right ascension (α) and declination (δ).

Precession of the equinoxes causes right ascension and declination to change slowly over time. Therefore, to correctly specify the position of a celestial object, one must give not only its right ascension and declination, but also the epoch for which those coordinates apply.


equinox

One of the two points at which the ecliptic intersects the celestial equator. This term is also applied to the moment the sun crosses such a point.

See autumnal equinox and vernal equinox.


escape velocity

The velocity a body much reach to break away from the gravity of another body and never return to it. In order for a planet or a moon to maintain an atmosphere, its escape velocity must be higher than the velocities of the atoms and molecules that make up its atmosphere.

Planets like Venus and the earth are too small to hold on to hydrogen and helium gases, and so their atmospheres are made up of heavier gases such as carbon dioxide, nitrogen, and oxygen.

Planets such as Jupiter and Saturn are much more massive and have therefore been able to hold onto the hydrogen and helium gases in their original atmospheres.


evening star

A term used to describe the planet Venus when it appears in the western sky after sunset.

The ancient Greeks referred to Venus as Hesperus when it appeared in the evening sky.


Fahrenheit scale (F)

A temperature scale that sets the freezing point of water at 32 degrees and the boiling point of water at 212 degrees. Because there are 180 divisions between the freezing and boiling points of water, the size of a degree in the Fahrenheit scale is smaller than the size of a degree in the Celsius and Kelvin scales which have only 100 divisions.

The Fahrenheit scale was invented in 1709 by the German physicist Gabriel Daniel Fahrenheit (1686-1736).


fireball

A term used for a very bright meteor, one that far exceeds the brightness of the planet Venus. As many as 100,000 fireballs occur in the earth's atmosphere each year.


first quarter

A term used to describe the appearance of a planet or moon when 50 percent of the its disk is illuminated by sunlight and when the planet or moon will subsequently enter a waxing gibbous phase.


Flamsteed number

A number assigned to stars in each constellation.

This system of star names was introduced in 1725 by English astronomer John Flamsteed (1646-1719) in his book Historia Coelestis Britannica, published posthumously. Stars within each constellation are numbered in order of right ascension. Flamsteed assigned numbers to about 3,000 stars in total.


flare

An energetic, temporary outburst of light observed in some stars, including the sun.


full

A term used to describe the appearance of a planet or moon when its disk is fully illuminated by sunlight.


galactic cluster

A small star cluster, containing a few hundred stars at most, located in the spiral arms or disk of our galaxy. Galactic clusters are also know as open clusters.


galactic coordinate system

A coordinate system in which the fundamental reference circle is the galactic equator and the zero point is the direction of the galactic center. The coordinates are named galactic longitude (l) and galactic latitude (b).


galactic equator

The plane of our galaxy, the Milky Way, projected onto the celestial sphere. The galactic equator and the celestial equator are inclined at an angle of about 62 degrees.


galactic latitude (b)

The angular distance of a celestial object above or below the galactic equator. Galactic longitude and galactic latitude are coordinates in the galactic coordinate system.

Galactic latitude is usually measured in units of degrees, minutes, and seconds of arc from 0 degrees to 90 degrees for latitudes above the galactic equator, and from 0 degrees to -90 degrees for latitudes below the galactic equator.


galactic longitude (l)

The angular distance of a celestial object east of the galactic center. Galactic longitude and galactic latitude are coordinates in the galactic coordinate system.

Galactic longitude is usually measured in units of degrees, minutes, and seconds of arc from 0 degrees to 360 degrees.


galaxy

A large collection of gravitationally bound stars and interstellar gas and dust. Galaxies typically are composed of hundreds of millions or even hundreds of billions of stars and their diameters range from a few thousand to hundreds of thousands of light years.

Many galaxies are flat disks that have a spiral appearance. Many others are elliptical and show no structural features. The rest are irregular in shape.

The galaxy that contains our solar system is a spiral galaxy called the Milky Way. It is composed of approximately 200 billion stars and is about 100,000 light years in diameter. The solar system is located about 30,000 light years from the center of the Milky Way galaxy.

The most distant object you can see with your naked eyes is the Andromeda galaxy. In a dark location far away from city lights you should be able to see this galaxy as a faint smudge just to the west of the star ν Andromedae. If you do see the Andromeda galaxy, you'll be seeing light that has been traveling across space for more than 2 million years to reach your eyes.


Galilean satellites

A term used to describe the four largest satellites or moons of Jupiter, discovered independently by Galileo Galilei (1564-1642) and Simon Marius (1573-1624) in 1610. Their names, in order of distance from Jupiter, are Io, Europa, Ganymede, and Callisto.

Although they are frequently referred to as the Galilean satellites, their names were given them by Marius, not Galileo.


gegenschein

A spot of light in the sky at a point 180 degrees from the sun.

Gegenschein is also called counterglow.


geocentric coordinates

The coordinates of a celestial body measured from the earth's center. For nearby objects such as the sun, moon, and planets, the difference between geocentric and topocentric coordinates is significant due to the effect of parallax.


giant

A term used to describe a star that has completed the "dwarf" or "main sequence" stage of stellar evolution, and is generating energy by converting into helium into carbon and oxygen. Stars spend a small fraction of their lifetime in the "giant" stage of stellar evolution.


gibbous

A term used to describe the appearance of a planet or moon when between 50 and 100 percent of the its disk is illuminated by sunlight. In other words, when the phase of the planet or moon is between first quarter and full, or between full and last quarter.


globular cluster

A large star cluster, often containing more than 100,000 stars, located outside the spiral arms or disk of our galaxy.


great circle

Any circle on the surface of a sphere generated by a plane passing through the center of the sphere. Such a circle has the same radius as the sphere.

Lines of longitude on the surface of the earth are great circles, as are lines of declination on the celestial sphere.


Gregorian calendar

In the Julian calendar established during the days of the Roman Empire, each year was 365 days long and every fourth year was made 366 days long by the addition of a leap day. This made a year 365.25 days long, which is over 11 minutes longer than the tropical year of 365.24219 days. Every 128 years this error accumulated into a full day, and by 1582 the first day of spring was occurring on March 11 instead of March 21.

Pope Gregory XIII was advised to correct this problem. First, he proclaimed that October 4, 1582 was to be followed by October 15, 1582. This eliminated the accumulated error of 10 days. Second, he proclaimed that century years, which are leap years in the Julian calendar, would henceforth only be considered leap years if they were evenly divisible by 400. The Gregorian calendar is correct to 1 day in 3,300 years.

Note that different countries made the switch from the Julian to the Gregorian calendar at different times. The Roman Catholic countries made the switch in 1582. Portions of the Netherlands did not switch until 1700. England and her colonies did not switch until 1752. Russia did not switch until 1917, and by this time the Julian calendar error had increased such that they had to omit 13 days.


harvest moon

A term used for the full moon closest to the autumnal equinox. The harvest moon gets its name from the fact that it rises soon after sunset, giving farmers more light and extra hours to harvest their crops.


horizon

A great circle that corresponds to the intersection of the earth and the sky.


horizontal coordinate system

A coordinate system in which the fundamental reference circle is the horizon and the zero point is the north point. The coordinates are named altitude (h) and azimuth (A).


hour angle (HA or t)

The angle measured westwards along the celestial equator from an observer's meridian to the hour circle of a celestial body. Hour angle is usually measured in units of hours, minutes, and seconds between 0 hours and 24 hours.


hour circle

Any great circle on the celestial sphere along which declination is measured. A great circle passes through the celestial poles and is perpendicular to the celestial equator.


hunter's moon

A term used for the first full moon following the harvest moon.


illumination

The percentage of the visible disk of a planet or the moon that is illuminated by sunlight.


inclination (i)

Axial inclination is the angle between the rotation axis of a celestial body and a line perpendicular to its orbital plane.

Orbital inclination is the angle between the orbital plane of a planet, satellite, asteroid, or comet and the plane of the ecliptic.


inferior conjunction

The moment at which the elongation of a celestial body on the near side of the sun is 0 degrees.


inferior planet

Mercury or Venus. These planets are referred to as inferior planets because they are closer to the sun than the earth.

The two inferior planets are always close to the sun in the sky. In fact, Mercury can never be more than about 28 degrees from the sun, and Venus can never be more than 48 degrees from the sun. These angular distances are known as the greatest elongations of these planets. The consequence of this is that unlike the other planets, Mercury and Venus can never be seen at midnight. They always rise or set within a few hours of the sun.

When either planet is west of the sun, it rises before the sun and is known as a "morning star". Either planet is described as an "evening star" when it is east of the sun and sets after the sun.

Mercury is the most difficult of the naked-eye planets to observe, because it is usually lost in the sun's glare. It can only be seen under favorable conditions at dusk or dawn when it is low on the horizon and our view of it is poor. Mercury is not very interesting when observed through a small telescope. Venus is the brightest point of light in the sky, and is fun to see for that fact alone. Through a small telescope Venus shows phases much like the moon's but its cloud cover prevents any surface features from being seen.


inner planet

Mercury, Venus, the earth, or Mars. These planets lie closer to the sun than the main belt of asteroids found between the orbits of Mars and Jupiter.


intergalactic

Between the galaxies. The void between the galaxies is called intergalactic space.


interplanetary

Between the planets. The void between the planets is called interplanetary space.


interstellar

Between the stars. The void between the stars is called interstellar space.


irregular galaxy (I)

A galaxy that does not posses a smooth distribution of stars or rotational symmetry. Neither an elliptical nor a spiral galaxy.


Julian calendar

The calendar established by the Roman Emperor Julius Caesar in 46 BC and modified by Augustus Caesar in 8 AD. The new months of July and August were named after these men.

Each year was 365 days long and every fourth year was made 366 days long by the addition of a leap day. This made a year 365.25 days long, which is over 11 minutes longer than the tropical year of 365.24219 days. Every 128 years this error accumulated into a full day, and it was eventually necessary for a new calendar, the Gregorian calendar, to be adopted to solve this problem.


Julian date

The number of days that have passed since noon universal time on January 1, 4713 BC. The Julian day is the number of integral days that have passed, whereas the Julian date includes the decimal fraction of the day that has elapsed since the preceding noon. Note that a Julian date is not a date on the Julian calendar.

The Julian date is very useful because the consecutive numbering of days makes the system independent of the varying lengths of months and years. To find the number of days between two events, simply determine the Julian dates of those events and subtract one date from the other.

The Julian date system was invented in 1582 by the French scholar Joseph Scalinger.


Kelvin scale (K)

A temperature scale that sets the freezing point of water at 273 degrees and the boiling point of water at 373 degrees. Because there are 100 divisions between the freezing and boiling points of water, the size of a degree in the Kelvin scale is larger than the size of a degree in the Fahrenheit scale which has 180 divisions.

The Kelvin scale was invented in 1848 by British physicist William Thomson (1824-1907), also known as Lord Kelvin.


last quarter

A term used to describe the appearance of a planet or moon when 50 percent of the its disk is illuminated by sunlight and when the planet or moon will subsequently enter a waning crescent phase.


latitude

The angular distance of a terrestrial location north or south of the equator. Longitude and latitude are coordinates in the terrestrial coordinate system.

Latitudes are usually measured in units of degrees, minutes, and seconds of arc from 0 degrees to 90 degrees for latitudes north of the equator, and from 0 degrees to -90 degrees for latitudes south of the equator.


light year (ly)

The distance that light or any other form of electromagnetic radiation travels in a vacuum in the course of a year. Contrary to popular belief, a light year is not a unit of time.

Light travels at about 300,000 kilometers per second or 186,200 miles per second. A light year is therefore equivalent to about 9,500,000,000,000 kilometers or 6,000,000,000,000 miles.


limb

The edge of the visible disk of the sun, moon, or any planet, or of any other celestial object that has a detectable disk.


local sidereal time (LST)

The sidereal time at an observer's location. It is equal to the right ascension currently on the observer's celestial meridian.


longitude

The angular distance of a terrestrial location east or west of the meridian that passes through Greenwich, England. Longitude and latitude are coordinates in the terrestrial coordinate system.

Longitude is usually measured in units of degrees, minutes, and seconds of arc from 0 degrees to 180 degrees for longitudes east of Greenwich, and from 0 degrees to -180 degrees for longitudes west of Greenwich.


luminosity (L)

A measure of the intrinsic or absolute brightness of a star. Luminosity is equal to the total energy radiated by a star per unit time.


luminosity classes

Luminosity classes are Roman numerals used to express the size of stars. Small stars have dense atmospheres that exhibit high gas pressures, whereas large stars have immense, extended atmospheres that exhibit low gas pressures.

The characteristics of absorption lines and bands in the spectra of stars are highly dependent on atmospheric pressure, and therefore are an indication of a star's size. These characteristics are studied to determine the luminosity class of a given star.


lunar eclipse

The passage of the moon through the earth's shadow.

A lunar eclipse can only occur when the moon is full. Rather than the earth passing into the moon's shadow, which is what happens when a solar eclipse occurs, during a lunar eclipse it is the moon that passes into the earth's shadow.

If the moon passes into the umbra of the earth's shadow, an observer sees a total lunar eclipse, and if the moon only passes into the penumbra of the earth's shadow an observer sees a partial lunar eclipse. Total lunar eclipses typically last an hour and a half.


magnitude

A logarithmic scale used to describe the brightness of an object. The larger the magnitude, the dimmer the object.

Magnitudes are used in astronomy for historical reasons. In ancient times, 129 BC to be exact, the Greek astronomer Hipparchus ranked the stars in six classes of magnitude when he produced the first well-known star catalog. The brightest stars were assigned to the first magnitude and the faintest stars just visible to the naked eye were assigned to the sixth magnitude.

More recently, this system had to be expanded to cover stars brighter than first magnitude and fainter than sixth magnitude. In 1856 the English astronomer Norman R Pogson proposed that a difference of five magnitudes correspond exactly to a brightness ratio of 100 to 1. The brightness ratio of two stars that differ by one magnitude is the fifth-root of 100, or 2.512, a quantity known as the Pogson ratio. A star that is two magnitudes brighter than another star is 2.512 squared, or about 6.3, times brighter than the other star.


main sequence (MS)

A term used to describe a typical star such as the sun that is generating energy by converting hydrogen into helium. Stars spend most of their lifetime in the "main sequence" or "dwarf" stage of stellar evolution.


mantle

The inner part of a planet between its central core and its outer crust.


mare (plural: maria)

An impact basin on the surface of the moon that has been filled with dark, basaltic lava. Such lava flows cover about 17 percent of the moon's surface.


mass (M)

A measure of the quantity of matter in a body, usually measured in units of grams or kilograms. Mass is also frequently measured in units of the mass of another body such as the earth or the sun. The mass of a body determines the strength of the gravitational field it produces.


mean solar time

Time measured with respect to the mean sun. Clocks display time based on the mean sun.

The earth's orbit around the sun is not a perfect circle but is an ellipse. The earth does not move along this ellipse at constant speed, but moves fastest when it is closest to the sun and slowest when it is farthest from the sun. The apparent sun therefore moves along the ecliptic at a non-uniform rate.

The non-uniform motion of the apparent sun implies that the length of the solar day is dependent on the position of the earth in its orbit. This situation is not desirable for civil timekeeping. Ideally we want to be able to treat each day as if it was exactly 24 hours long. The mean sun, which moves along the celestial equator at a uniform rate, was invented with this goal in mind.


meridian

A great circle on the surface of the earth that passes through both poles of the earth's axis. In other words, an observer's meridian is the line of longitude he or she is standing on.

In astronomy, when someone says "meridian" he or she usually means the celestial meridian.


Messier catalog

A list of non-stellar objects compiled by French astronomer Charles Messier (1730-1817) and published in 1784. Messier was interested in discovering comets. Between 1760 and 1784 he compiled a list of nebulous objects that might be confused with the comets for which he was searching.


meteor

A streak of light in the sky produced by the motion of a meteoroid through the earth's atmosphere. Meteors are typically observed 100 kilometers or 60 miles high in the atmosphere and burn up before ever getting near the ground.

On a clear, moon-less night an average of about 10 meteors can be seen per hour. Much higher counts are possible during a meteor shower. The highest meteor count occurs during the early morning hours when the earth is moving into the cloud of interplanetary particles that cause meteors.

Meteors are commonly called falling stars or shooting stars.


meteoroid

A small particle orbiting the sun. Most are thought to be fragments of asteroids. Most are also very small, about the size of a grain of sand.

It is estimated that several hundred tons of meteoroids fall on the earth each day. Almost all burn up in the atmosphere and do not strike the ground. Those that do are called meteorites.


meteorite

The portion of a meteoroid that has survived its fall from the sky and has landed on the surface of the earth.

The "thunderstone" ("Donnerstein" in German) that fell near Einsisheim, Alsace in 1492 was the first documented case of a meteorite. Meteorites were not accepted as being extraterrestrial in origin by the scientific community until 1803.


meteoritics

The study of meteorites and of the formation of the solar system.


meteor shower

A profusion of meteors that typically fall within a day or two and appear to radiate from a common point in the sky. Meteor showers are caused by the passage of the earth through a meteor stream. Such streams are composed of the particles left behind by comets as they near the sun.


Milky Way

The galaxy that contains the solar system. The approximately 200 billion stars that compose the Milky Way galaxy are concentrated in a plane, and our view of this plane of stars from within results in the faint band of light we also call the Milky Way. It is necessary to view the sky on a clear, moon-less night to see the Milky Way.

The Milky Way galaxy is thought to be a spiral galaxy of type Sb or Sc.


minor planet

Another name for an asteroid.


moon

Any natural body that revolves around a planet. Although we refer to our planet's natural satellite as "the moon" there are in fact many other moons in our solar system. In fact, the only planets that do not possess one or more moons are Mercury and Venus.

In ancient times the moon was used as the basis for calendars, and this explains why our month is about as long as the moon's synodic period, that is, the length of time it takes the moon's phases to repeat themselves. It is also no coincidence that we divide our months into weeks lasting seven days, because it takes about one week for the moon to go from new to first quarter, from first quarter to full, from full to last quarter, and from last quarter to new.

One of the moon's characteristics we take for granted is that we see the same side of the moon all the time. The "man in the moon" is always visible. The reason for this is that the moon rotates once on its axis each time it revolves around the earth. The moon moves rapidly across the sky, an average of 13 degrees per day eastward. During the course of one evening it is possible to notice the motion of the moon against the background stars. Because of the moon's eastward motion, it rises about 50 minutes later each day.

The period of time it takes the moon to pass through the cycle of phases is about 29.5 days. This period is called the moon's synodic period. It takes the moon only 27.3 days to circle the earth. This period is called the moon's sidereal period.


morning star

A term used to describe the planet Venus when it shines in the eastern sky before sunrise.

The ancient Greeks referred to Venus as Phosphorus when it appeared in the morning sky.


nadir

The point on the celestial sphere that lies directly beneath an observer, 90 degrees below the horizon. This point lies directly opposite the observer's zenith and is therefore never observable.


nautical twilight

The period between the time the sun is 6 degrees and 12 degrees below the horizon.


nebula (plural: nebulae)

Originally, any diffuse, non-stellar object. Galaxies were originally referred to as nebulae. This term now describes a cloud of gas and dust in interstellar space.

The two major types of nebulae are diffuse nebulae and planetary nebulae.


neutron star

A star more massive than the sun, yet only about 20 kilometers (12.4 miles) in diameter. A neutron star is a dense ball of neutral subatomic particles left at the core of a star after a supernova explosion destroys the rest of the star. A star that is not massive enough to form a neutron star at the end of its life ends up as a type of star called a white dwarf. A star that is too massive to form a neutron star collapses and forms a black hole.


new

A term used to describe the appearance of a planet or moon when its disk is not illuminated by sunlight.


New General Catalogue

Short for New General Catalogue of Nebulae and Clusters of Stars. A list of non-stellar objects compiled by Danish astronomer John Louis Emil Dreyer (1852-1926) and published in 1888.


node

The point in an orbit at which it crosses the ecliptic or another reference plane. The node at which the orbiting body crosses the ecliptic from south to north is called the ascending node. The node at which it crosses from north to south is called the descending node.

Because the sun is always on the ecliptic, the only time a solar eclipse can occur is when the moon is near one of its nodes.


north point

The point on the horizon at 0 degrees azimuth.


North Star

Polaris, known more formally as α Ursae Minoris, or any other bright star that happens to be within a few degrees of the north celestial pole during a given era.


nova (plural: novae)

A star that experiences a dramatic increase in its brightness for a short period of time, and then slowly returns to its original brightness. During a nova outburst a star can increase its luminosity by hundreds or even thousands of times.

It is thought that novae are binary star systems, and that the increase in brightness happens when one star dumps some of its mass onto the surface of the other star.


nuclear fusion

A process whereby several small particles are combined into a larger particle whose mass is slightly less than the combined masses of the small particles. The lost mass is converted into energy. This is the source of energy in all stars, including the sun.


occultation

The passage of a larger celestial body in front of a smaller one. A solar eclipse is really an occultation of the sun by the moon.


open cluster

A small star cluster, containing a few hundred stars at most, located in the spiral arms or disk of our galaxy. Open clusters are also know as galactic clusters.


opposition

The moment when a planet's elongation is 180 degrees.


orbit

The path along which a celestial body moves in the gravitational field of another body. For example, the path of the earth or another planet around the sun, the path of an artificial satellite around the earth, or the path of one star around another star.

Orbits are conic sections. That is, they are either ellipses, parabolas, or hyperbolas. Most orbits are ellipses, and the orbits of the planets of the solar system are almost circular. The orbits of periodic comets are ellipses.


orbital inclination

The angle between a body's orbital plane and the earth's orbital plane.


outer planet

Jupiter, Saturn, Uranus, Neptune, or Pluto. These planets lie farther from the sun than the main belt of asteroids found between the orbits of Mars and Jupiter.


parallax

The angular displacement in the apparent position of a celestial body when observed from two widely separated points.

Measuring the parallax of stars is very useful because it allows us to measure the distances to those stars. The position of a star is measured very precisely at one time, then this measurement is repeated half a year later when the earth has moved to the other side of its orbit. The star will have a slightly different position when viewed from these two perspectives, and the different in these positions allows the distance of the star to be calculated.

The German astronomer Friedrich Wilhelm Bessel (1784-1846) measured the first stellar parallax, that of 61 Cygni, in 1838.


parsec (pc)

A unit of length equal to the distance at which the mean radius of the earth's orbit subtends an angle of one arc second.

Parsecs are used to specify the distances of objects outside our solar system, such as the distances of stars and galaxies. One parsec is equal to 206,265 astronomical units, or 3.26 light years.


partial eclipse

An eclipse in which the eclipsed body is not totally hidden by the eclipsing body.


penumbra

A term used to describe the region of partial shadow in an eclipse, as well as the lighter part of a sunspot.


perigee

The point in an object's orbit around the earth at which it reaches its nearest distance to the earth.


perihelion

The point in an object's orbit around the sun at which it reaches its nearest distance to the sun.


photosphere

The visible surface of the sun or any other star. The photosphere is the region of a star's atmosphere that contributes most of the visible light that we see when we look at the star. Sunspots are observed in the photosphere.


planet

A spherical body that orbits the sun or any other star and shines only by reflected light. The nine planets of the solar system are Mercury, Venus, the earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.

Planets that are closer to the sun move faster across the sky than planets that are farther away. The planets appear to move slowly eastward with respect to the stars, a fact which gave them their name, as "planet" means "wanderer" in Greek. Occasionally a planet will slow down in its prograde or eastward motion and temporarily move westward. This motion is called retrograde motion.

The planets do not move at random over the sky but stay close to the line called the ecliptic. The ecliptic is the line along which the sun moves, and is simply the projection of the earth's orbit onto the celestial sphere. The reason all the planets move close to this line is that their orbits lie nearly in the same plane as the orbit of the earth. In fact, you'll find all planets other than Pluto within about 7 degrees of the ecliptic. Pluto's orbit is more highly inclined to the plane of the ecliptic, and so you'll find that planet as much as 17 degrees away.


planetarium

An optical device for projecting a representation of the sky on a domed ceiling. Also, a building housing such a device.


planetary nebula

A cloud of gas and dust in interstellar space, measuring on average a light year across. Planetary nebulae consist mostly of hydrogen, helium, nitrogen, and oxygen.

A planetary nebula is an expanding shell of gas ejected from the outer atmosphere of a giant star in the late part of its life.

Planetary nebulae have nothing whatsoever to do with planets. These nebulae are called "planetary" because as seen through a small telescope they resemble the disk of a distant planet.


pole star

The star closest to the north or south celestial pole at any particular time.


precession

The periodic change in the direction of the earth's axis of rotation. Currently the North Pole of the axis of rotation points toward the star Polaris, known more formally as α Ursae Minoris.

The earth is not a perfect sphere, but has an equatorial diameter that is slightly larger than its polar diameter. The sun, moon, and other planets of the solar system exert a gravitational attraction on the equatorial bulge of the earth. It is this force that is responsible for precession.

The positions of the celestial poles actually move across the sky, tracing out a circle with a diameter of about 47 degrees on the celestial sphere every 25,800 years. Therefore, the pole star observed thousands of years ago was not the star we see near the north celestial pole today. For example, in Egypt when the great pyramids were being built, the North Star was Thuban, known more formally as α Draconis, the brightest star in the constellation Draco.

Precession does not alter the constellation outlines or change their boundaries with respect to the stars, but causes a slow drift of the entire celestial coordinate system on the celestial sphere.


prograde motion

The apparent west to east motion of a planet as seen from the earth against the background of stars. Prograde motion is also described as direct motion.


prominence

Solar material elevated above the surface by the magnetic forces found in active regions on the solar surface.


proper motion (μ)

The apparent angular motion of a star across the celestial sphere. Stars do actually move through space, and the change in their position with respect to the moving the solar system causes their apparent position to change.

Because stars are so far away, it takes thousands of years for stars to move far enough for this effect to be noticeable to the naked eye.

Proper motion was discovered by the English astronomer Edmund Halley (1656-1742) around 1715 when he compared the position of the star Arcturus, known more formally as α Bootis, with its position in ancient star charts.


proper name

A name, such as Altair or Betelgeuse, given to one of the brighter stars in the sky.


pulsar

A rapidly rotating neutron star that emits radiation in narrow beams focused by its strong magnetic field. These beams act like the beams of light from a lighthouse. When either beam crosses our line of sight we see a "flash" from the pulsar.


quadrature

The moment when a planet's elongation is 90 degrees.


quasar

One of a number of star-like objects found at great distances from our own galaxy, now known to be the centers of very young galaxies.

The term "quasar" is a contraction of the phrase "quasi-stellar radio source". Such objects were first detected by radio telescopes due to their strong radio emissions.


radiant

The point from which all the meteors in a meteor shower appear to radiate.


radiation

Energy propagating through space in the form of electromagnetic waves.


reflection nebula

A nebula that reflects the light of cool stars in our direction.


retrograde motion

The apparent east to west motion of a planet as seen from the earth against the background of stars. Such apparent backward motion occurs when the earth is overtaken by an inferior planet near inferior conjunction or overtakes a superior planet near opposition. The result is that the planet appears to slow down, reverses its direction, slows down again, and then continues its "normal" prograde or direct motion.


revolution

The orbital motion of a body around a gravitational center of attraction.


right ascension (RA or α)

The angular distance of a celestial object east or west of the vernal equinox to the hour circle of the object. Right ascension and declination are coordinates in the equatorial coordinate system.

Right ascension is analogous to longitude on the earth's surface. Right ascension is usually measured in units of hours, minutes, and seconds from 0 hours to 24 hours. The benefit of using these units is that as the earth rotates you see the sky turn by about one hour of right ascension for each hour of time.


rotation

The turning of a body on its axis. Almost all celestial bodies show some degree of rotation.


satellite

Any body, natural or artificial, that revolves around a planet. Natural satellites are commonly referred to as moons.


semi-major axis

The average distance of an orbiting body from the object it orbits.


sidereal day

The time interval between two successive meridian passages of a star. A sidereal day is divided into 24 hours, and is equal to about 23 hours, 56 minutes, and 4 seconds of mean solar time.


sidereal time

Time measured by reference to the rotation of the earth with respect to the stars. Our common solar time is measured by reference to the rotation of the earth with respect to the sun.

With respect to the stars, the earth takes about 23 hours, 56 minutes, and 4 seconds to spin once on its axis. This quantity is known as a sidereal day. During this period the earth moves along its orbit around the sun. Because of this motion, it takes roughly another four minutes before the earth has rotated once on its axis with respect to the sun. This 24-hour period is known as a solar day.

The sidereal time at any location is equal to the hour angle of the vernal equinox.


solar day

The time interval between two successive meridian passages of a sun. A solar day is 24 hours long.


solar eclipse

A solar eclipse can only occur when the moon is new. The moon's orbit is inclined about five degrees with respect to the ecliptic and intersects the ecliptic at two points known as the nodes of the orbit. If the moon's orbit was not inclined to the ecliptic, we would observe solar eclipses every month because the moon would pass over the sun's disk every month. But, because the moon's orbit is inclined by five degrees, most of the time the moon passes above or below the sun. An eclipse occurs only when the moon and the sun are both near one of the nodes of the moon's orbit.

The moon casts a shadow, and when this shadow sweeps across the surface of the earth people in the shadow see an eclipse. Observers in the area swept across by the umbra, the darkest part of the shadow, see a total solar eclipse. The solar disk is completely blocked in this case, allowing view of the sun's chromosphere, corona, and prominences. The moon's umbra is only about 270 kilometers (168 miles) across, and moves so quickly that a total solar eclipse typically lasts only 3 or 4 minutes. The area surrounding the umbra is called the penumbra, and observers in the area swept across by the penumbra see only a partial eclipse. An annular eclipse occurs when the moon is farther than normal from the earth, and is therefore too small to completely cover the sun. When the moon passes in front of the sun observers see a ring (annulus) of sun surrounding the moon's disk.

It is a remarkable coincidence of nature that the sun and moon are nearly the same size in the sky. The sun is about 400 times larger than the moon, but it is also about 400 times farther way from the earth. It is a fact that the moon is slowly moving away from the earth, so sometime in the distant future total solar eclipses will no longer be possible.


solar system

The sun and a large number of objects gravitationally bound to it. These objects include the nine planets Mercury, Venus, the earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto; the moons of the nine planets; and numerous asteroids, comets, and meteoroids.

The solar system is located about 30,000 light years from the center of the Milky Way galaxy.


solar time

Time measured by reference to the rotation of the earth with respect to the sun.


solstice

One of the two points at which the sun reaches its northernmost or southernmost points on the ecliptic. The northernmost point is called the summer solstice and the southernmost point is called the winter solstice. This term is also applied to the moment the sun reaches such a point.


south point

The point on the horizon at 180 degrees azimuth.


spectral sequence

A sequence of letters assigned to stars to order them by decreasing temperature in the classification scheme of spectral types. The sequence consists of O, B, A, F, G, K, and M, where O represents the hottest stars and M represents the coolest stars. O stars are rare but very bright. M stars are numerous but relatively faint. The sun is a star of type G.


spectral types

Letters and numbers used to express the surface temperatures of stars.

The characteristics of absorption lines and bands in the spectra of stars are highly dependent on temperature, and so these characteristics are studied to determine the spectral type of a given star.

If you take a look at stars in the sky you'll see that they're not all white. Many appear to have a pure white color, but many others appear to have a touch of blue in their light, while others appear to have a touch of yellow, or orange, or even red.

These colors you see are indications of the surface temperatures of these stars. The blue stars are the hottest, and the red stars are the coolest. Stars are classified into spectral classes, named O, B, A, F, G, K, and M, based on the characteristics of their light, which are in turn dependent on their surface temperatures.


spectrum (plural: spectra)

The display of the dispersal of radiation from an object into its constituent wavelengths. Such a display allows one to observe the wavelengths present in the radiation and their relative intensities.

One familiar example of a spectrum is a rainbow, in which the visible wavelengths of sunlight are dispersed so that the sequence red, orange, yellow, green, blue, indigo, and violet can be observed. In this case sunlight is dispersed when it passes through drops of rain. Starlight can be dispersed by passing it through a prism or a grating.

Because the characteristics of absorption lines and bands in the spectra of stars are highly dependent on both temperature and atmospheric pressure, these physical properties of stars can be determined from their spectra.


spiral galaxy (S or SB)

A galaxy that appears to have stars concentrated in a spherical nuclear bulge or oblong central bar, and a flat disk with young stars concentrated in spiral arms, giving the galaxy the appearance of a pinwheel.

Spiral galaxies are divided into two types, normal spirals and barred spirals.

S	the spiral arms curve outward directly from the spherical central bulge

SB	the spiral arms begin on opposite ends of an oblong central bar

Additionally, spiral galaxies are classified according to the prominence of their nuclear bulge or central bar and the degree of spiral arm winding.

a	nuclear bulge or central bar dominates, spiral arms are tightly wound

b	nuclear bulge or central bar and spiral arms are equally prominent

c	nuclear bulge or central bar is small, spiral arms are loosely wound

The Milky Way galaxy is thought to be a spiral galaxy of type Sb or Sc.


star

A spherical, gaseous body that generates energy by nuclear fusion reactions in its core. These reactions, which convert hydrogen into helium and helium into heavier elements, allow a typical star to shine for billions of years.

Many stars appear to be white in color, but others appear to be blue, yellow, orange, or even red. These colors are related to the temperatures of the stars. Blue stars are hotter than white stars, which in turn are hotter than yellow stars. Orange stars are cooler than yellow stars, and red stars are the coolest of all.

Many of the stars you see in the sky are much like the sun. Some are many times brighter and hundreds of times larger than the sun. If such a star were placed where our sun is, the orbits of the inner planets, including that of the earth, would fall inside the star.

The sun is a typical star, one of about 200 billion stars that make up the Milky Way galaxy.


summer solstice

The moment when the sun reaches the northernmost point of the ecliptic, or that point itself. This occurs on or about June 21 and marks the beginning of summer in the Northern Hemisphere and the day having the maximum hours of sunlight. It also marks the beginning of winter in the Southern Hemisphere and the day having the maximum hours of darkness.


Summer Triangle

An asterism formed by Altair in Aquila, Deneb in Cygnus, and Vega in Lyra. This asterism is prominent during summer months in the Northern Hemisphere.


sun

The star that is the center of the solar system. The sun is a typical star in the Milky Way galaxy. In fact, if it were placed as far away from the earth as many typical stars are it would be nothing more than an inconspicuous point of light in the sky. But, because the sun is the center of our solar system and is much closer to us than any other star, the sun's appearance in our sky is unique.

Our solar system consists of the sun, nine planets plus their moons, as well as asteroids, comets, and meteoroids. Other stars are probably surrounded by similar systems of bodies, but astronomers are only now beginning to detect very large planets orbiting relatively nearly stars.

The term sun is sometimes used generally as a synonym for star.


sunspot

A region in the photosphere of the sun that is cooler than its surroundings, and therefore appears dark by contrast.


sunspot cycle

The variation in the number of sunspots, which repeats itself about every 11 years.


supergiant

A term used to describe a star that has completed the "giant" stage of stellar evolution, and is nearing the end of its lifetime. Stars spend a very small fraction of their lifetime in the "supergiant" stage of stellar evolution.


superior conjunction

The moment at which the elongation of a celestial body on the far side of the sun is 0 degrees.


superior planet

Mars, Jupiter, Saturn, Uranus, Neptune, or Pluto. These planets are referred to as superior planets because they are farther from the sun than the earth.

Mars is the closest superior planet to the earth, and therefore moves more quickly across the background of stars than do Jupiter and Saturn. Superior planets such as Mars are best seen when they are at opposition, that is, when the earth is between them and the sun. Because Mars's orbital period is slightly less than twice as long as the earth's, Mars does not reach opposition once every year. Oppositions occur about two years and two months apart. This means that Mars is in a favorable position for observation from the earth only half as often as are the other superior planets.

Jupiter appears as a very bright yellow "star" in the sky and is easily differentiated from a real star. Saturn, on the other hand, is faint enough to be confused with a bright star. Jupiter and Saturn move much more slowly than Mars and both reach opposition about once a year as the earth moves between them and the sun. Jupiter, with its colored bands and four bright moons, and Saturn, with its spectacular rings, are arguably the most interesting planets to observe through a small telescope.

Uranus, Neptune, and Pluto require the aid of binoculars or a telescope to be seen. If you own a telescope you may be able to observe Uranus as a small greenish disk. Neptune's bluish disk is even smaller and significantly fainter. Pluto is far too faint to observe unless you have a large telescope, good seeing conditions, and detailed star charts. Uranus, Neptune, and Pluto move slowly across the background of stars. In fact, Pluto has completed only about a quarter of its orbit since its discovery in 1930, because it has an orbital period of over 248 years.


supernova (plural: supernovae)

A star that experiences a catastrophic explosion of its core, resulting in a spectacular increase in its energy output. Such an explosion marks the final stage of evolution of a massive star. During a supernova explosion a star can increase its luminosity by millions of times.


supernova remnant

The rapidly expanding gases produced by a supernova explosion.


synodic period

For the moon, the average length of time between a given phase and the next phase of the same type. For a planet, the average length of time between successive oppositions, conjunctions, or quadratures.


terminator

The dividing line between the illuminated and dark portions of the lunar disk or any planetary disk. The line of sunrise or sunset on that body.


topocentric coordinates

The coordinates of a celestial body measured from the earth's surface. For nearby objects such as the sun, moon, and planets, the difference between topocentric and geocentric coordinates is significant due to the effect of parallax.


total eclipse

The complete hiding of one body by another as seen by an observer on the earth. In common usage a total eclipse of the sun is one in which the moon completely hides the sun's disk, and a total eclipse of the moon is one in which the moon's disk passes completely into the umbra of the earth's shadow.


transit

The passage of a celestial body across the meridian. Also, the passage of a small celestial body in front of a much larger one, such as when Mercury or Venus appear in silhouette against the solar disk, or when a natural satellite passes in front of Jupiter or Saturn. The shadow of a natural satellite may also transit the disk of the planet it orbits.


tropical year

The time interval between two successive passages of the sun through the vernal equinox. A tropic year is 365.24219 solar days long.


umbra

A term used to describe the region of total shadow in an eclipse, as well as the darker part of a sunspot.


universal time (UT)

Universal time is the mean solar time in the time zone centered on Greenwich, England. It is the same thing as Greenwich Mean Time (GMT).


universe

Everything there is. Another term for cosmos.


variable star

A star whose brightness varies with time. The period of time between successive peaks in the brightness of such a star can vary from hours to years. Some variable stars have very regular periods, and others have irregular periods. Some variable stars change their brightness so little that this change is only noticed after careful observation over time. Other variable stars change their brightness drastically, easily visible to the naked eye in the night sky, but then disappearing from view, only to brighten and reappear months later.

The most common type of variable stars are red giants that appear to pulsate, expanding and contracting like a beating heart.


vernal equinox

The moment when the sun crosses the celestial equator moving from south to north, or that point itself. This takes places about March 21 and marks the beginning of spring in the northern hemisphere and the beginning of fall in the southern hemisphere.

The sun crosses the celestial equator where the ecliptic and the celestial equator intersect. The point of the vernal equinox is also called the First Point of Aries and is important because it is the zero point for both the equatorial and ecliptic coordinate systems. That is, both right ascension and ecliptic longitude are measured eastward from this point.

The equinoxes are not fixed but move approximately 50 arc seconds per year due to the effect of precession. The vernal equinox or First Point of Aries is now actually located in the constellation Pisces.


vertical circle

A circle on the celestial sphere, drawn through the observer's zenith and perpendicular to the horizon.


wane

A term used to describe that portion of the lunar revolution between full and new, when the illuminated area of the disk is decreasing. Opposite of wax.


Water Jar

An asterism formed by the stars γ (Sadalachbia), η, π, and ζ in Aquarius.


wavelength (λ)

The distance between two crests of a wave.


wax

A term used to describe that portion of the lunar revolution between new and full, when the illuminated area of the disk is increasing. Opposite of wane.


west point

The point on the horizon at 270 degrees azimuth.


white dwarf

A star that is very near the end of its lifetime. Such a star has lost the ability to produce nuclear energy and as a consequence has collapsed to a size approximately that of the earth.


winter solstice

The moment when the sun reaches the southernmost point of the ecliptic, or that point itself. This occurs about December 21 and marks the beginning of winter in the Northern Hemisphere and the day having the maximum hours of darkness. It also marks the beginning of summer in the Southern Hemisphere and the day having the maximum hours of sunlight.


Winter Triangle

An asterism formed by Sirius in Canis Major, Procyon in Canis Minor, and Betelgeuse in Orion. This asterism is prominent during winter months in the Northern Hemisphere.


year

The time interval required for the earth to revolve once around the sun. The choice of reference point determines the exact length of the year.

Tropical year	equinox to equinox	365.24219 days

Sidereal year	fixed star to fixed star	365.25636 days

Anomalistic year	apse to apse	365.25964 days

Eclipse year	moon's node to moon's node	346.62030 days


zenith

The point on the celestial sphere that lies directly above an observer, 90 degrees above the horizon. This point lies directly opposite the observer's nadir.


zodiac

A band approximately 20 degrees wide passing around the celestial sphere centered on the ecliptic.

This band is divided into 12 equal sections 30 degrees in length called signs of the zodiac. The names of these sections correspond to the constellations located in them at the time of Hipparchus, over 2000 years ago.

The signs of the zodiac are called Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces. Precession of the equinoxes has shifted the zodiacal constellations by over 30 degrees meaning that the signs of the zodiac and the zodiacal constellations no longer correspond.

For example, spring begins when the sun enters the sign of Aries, but this point is now located in the constellation Pisces. Furthermore, during the course of one year the sun now passes through the constellation Ophiuchus, although this constellation is not considered a sign of the zodiac.


zodiacal constellation

One of the twelve constellations of the zodiac. The zodiacal constellations include Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, and Pisces. Note that the zodiacal constellations are not equivalent to the signs of the zodiac, although they once were. Note, too, that in astrology Scorpius and Capricornus or referred to as Scorpio and Capricorn.


zodiacal light

A faint glow that extends away from the sun in the ecliptic plane of the sky, visible to the naked eye in the western sky shortly after sunset or in the eastern sky shortly before sunrise. Zodiacal light is best seen on a clear, moon-less night in the tropical latitudes. Zodiacal light is sunlight scattered by very small dust particles in interplanetary space concentrated in the plane of the solar system.


Overview

CyberSky is an exciting, entertaining, and educational astronomy program that transforms your personal computer into your personal planetarium. CyberSky provides an excellent way to learn about astronomy and to explore the wonders of the sky visible in the distant past, the present, and the far-off future.

CyberSky displays accurate charts of the sky as seen from any location on the earth. Sky charts can include stars, constellations, deep sky objects, and solar system objects, and can be enhanced by the addition of labels, coordinate system grids, and reference lines. CyberSky's user-friendly interface allows you to easily change your view of the sky, search for celestial objects, and display data about those objects. CyberSky also prints attractive sky charts that you can take outside with you.

CyberSky was designed to be simple enough to appeal to people who are just beginning to discover astronomy, yet provide enough information to be useful to people who've already learned the basics. CyberSky has the ability to quickly and easily show you what's visible today or next weekend, but it is also accurate enough to help with research involving the appearance of the sky in the distant past, for example, during the era of pyramid construction in ancient Egypt.

CyberSky's ease of use and amazing animation feature make it an innovative and motivating learning environment. CyberSky provides an excellent way to learn the names and positions of the stars, constellations, and deep sky objects, and to become familiar with the motions of solar system objects across the sky. Many of the most basic and interesting astronomical phenomena can only be observed over weeks or months of time, and by observing the sky from widely separated locations. CyberSky lets you do this; it places the sky under your control.

CyberSky is used by people all over the world who want to learn about astronomy, by amateur and professional astronomers who need a straightforward planetarium program, by parents who want to share the joys of astronomy with their children, and by educators who want to empower their students to learn in a way unimagined a decade or two ago. CyberSky has something to offer you, regardless of your level of astronomy knowledge.


Features

Features of CyberSky 3.1 include:

General

•	Displays detailed, accurate, and dynamic views of the sky as seen from any location on the earth. You can move your viewpoint in any direction, even below the horizon, and can select from a wide range of zoom levels.

•	Allows you to search for stars, constellations, deep sky objects, solar system objects, and points on the celestial sphere.

•	Allows you to customize colors and fonts, and to customize screen and printer colors and fonts independently of each other.

•	Prints attractive sky charts on any type of printer supported by Windows.

•	Saves sky charts as bitmap files that you can use as Windows wallpaper.

Stars

•	The registered version of CyberSky includes 80,179 stars to magnitude 8.5, whereas the shareware version includes only 1,671 stars to magnitude 5.0.

•	Displays stars in white or in colors based on their spectral types.

•	Labels stars with their proper names, Bayer letters, Flamsteed numbers, or magnitudes.

•	Displays information about any star, including the star's proper name, Bayer and Flamsteed designations, equatorial and horizontal coordinates, magnitude, the constellation it is in, its rising, transit, and setting times, and its spectral type.

Constellations

•	Displays the official, internationally recognized constellation boundary lines that define each of the 88 constellations.

•	Displays attractive constellation figures, and allows you to view the figures of all 88 constellations or only those of the 12 zodiacal constellations.

•	Labels constellations with their official three-letter abbreviations, their official Latin names, or equivalent English or German names.

Deep sky objects

•	The registered version of CyberSky includes 472 deep sky objects to magnitude 8.5, whereas the shareware version includes only 68 deep sky objects to magnitude 5.0.

•	Labels deep sky objects with their popular names or catalog numbers.

•	Displays information about any deep sky object, including the object's name, catalog numbers, equatorial and horizontal coordinates, magnitude, the constellation it is in, its rising, transit, and setting times, and its type.

Solar system objects

•	Displays the positions of the sun, moon, and all planets in the solar system, including the phases of Mercury, Venus, and the moon, the four Galilean satellites of Jupiter, and the rings of Saturn.

•	Displays the paths of solar system objects across the sky. The positions of objects along their paths can be marked and labeled with the date and time.

•	Solar system objects can be locked to the center of the sky chart, making it possible to watch many interesting astronomical phenomena, including solar eclipses, occultations of stars by the moon, and the motions of the Galilean satellites around Jupiter.

•	Displays information about any solar system object, including the object's equatorial, horizontal, and ecliptic coordinates, distances from the earth and sun, elongation from the sun, angular diameter, magnitude, the constellation it is in, its rising, transit, and setting times, and the illumination of its disk.

Reference grids, lines, and points

•	Displays and labels equatorial and horizontal coordinate system grid lines.

•	Displays the ecliptic, celestial equator, and galactic equator.

•	Displays and labels the north and south ecliptic poles, celestial poles, and galactic poles.

Help system

•	Includes context-sensitive Help for all user interface items and for all dialog boxes.

•	Includes reference information about constellations and solar system objects, diagrams and tables, and a glossary of astronomical terms.

•	Includes explorations that suggest ways to use CyberSky to learn more about such topics as precession, proper motion, and the retrograde motion of the planets.


What's new

Changes introduced in CyberSky 3.0 include:

•	More viewpoint options: You can view the sky in any direction, even toward a point that's below the horizon. Double-click a point to move it to the center of the sky chart. Or, right-click a point and select the Center command on the popup menu that appears. Use buttons on the View toolbar to scroll the sky chart. Use the arrow keys by themselves to scroll the sky chart in large steps, or with a Ctrl key to scroll in smaller steps.

•	More zoom levels: You can view the sky at zoom levels between 1X and 8192X. Use buttons on the View toolbar to zoom in or out. Or, press the PgUp or PgDn key. Or, right-click the sky chart and select the Zoom In or Zoom Out command from the popup menu that appears. Use the Zoom Level command on the View menu to set the zoom level to a specific value. Use the 1 through 0 keys to set the zoom level to 1X through 512X. Use the mouse wheel to zoom in or out if you have a Microsoft IntelliMouse or similar mouse with a wheel.

•	Search capability: Search for a star, constellation, deep sky object, solar system object, or point on the celestial sphere. Searching for an object moves it to the center of the sky chart, even if it is below the horizon. Searching for a solar system object also locks the object to the center of the sky chart. Use the buttons on the Search toolbar to quickly search for solar system objects.

•	Many more stars: The registered version of CyberSky includes 80,179 stars to magnitude 8.5, almost 10 times the number of stars included with the previous registered version. (The shareware version includes only 1,671 stars to magnitude 5.0). Stars are displayed using smaller symbols, but you can select to use larger symbols if you wish. The limiting magnitude value for stars can be adjusted automatically as you zoom in or out. Stars can be labeled with their magnitudes.

•	Many more deep sky objects: The registered version of CyberSky includes 472 deep sky objects to magnitude 8.5, almost five times the number of deep sky objects included with the previous registered version. (The shareware version includes only 68 deep sky objects to magnitude 5.0). Deep sky objects are displayed in correct sizes and orientations whenever possible. The limiting magnitude value for deep sky objects is independent of the value for stars, and this value can be adjusted automatically as you zoom in or out.

•	Save Bitmap command: The Save Bitmap command on the File menu allows you to save sky charts as 8- or 24-bit bitmaps. The Bitmap Setup dialog box allows you to select a standard bitmap size, useful for making Windows wallpaper, or to specify another set of dimensions.

•	More printing options: The Page Setup dialog box, displayed when you use the Print or Print Preview command on the File menu, allows you to specify the sizes of margins around a printed sky chart, and whether to print in black and white or in color. The sizes of margins are specified in inches or centimeters, depending on the preference specified under Regional Settings in the Windows Control Panel.

•	More toolbars: The View, Animation, Chart, and Search toolbars give you easy access to many of the program's most frequently used features. The positions of all toolbars are remembered between sessions.

•	Data bar: The panes in the Data bar display the local and universal time and other information about the sky chart. Click a pane to access a dialog box or perform a related command. For example, click the pane that displays the local time to display the Local Time dialog box. The position of the Data bar is remembered between sessions.

•	Pointer bar: The panes in the Pointer bar display the equatorial coordinates, horizontal coordinates, and constellation under the mouse pointer. Click the equatorial or horizontal coordinates pane to turn the equatorial or horizontal coordinate system grid on or off, or the constellation pane to access the Constellations dialog box. The position of the Pointer bar is remembered between sessions.

•	Chart mode options: Use the Atlas Mode command on the Chart menu to align the sky chart with the equatorial coordinate system, or the Horizon Mode command on the Chart menu to align the sky chart with the horizontal coordinate system.

•	Object disks: Solar system objects are displayed as disks with correct sizes, orientations, and phases whenever possible. You can see the moon move across the sun during a solar eclipse, and can observe transits of Mercury and Venus. You can also see the phases of Mercury and Venus as these planets orbit the sun.

•	Galilean satellites: The four Galilean satellites of Jupiter, called Io, Europe, Ganymede, and Callisto, are displayed whenever you zoom in to view the planet at 256X or higher magnification.

•	Saturn's rings: The rings of Saturn are displayed whenever you zoom in to view the planet at 1024X or higher magnification.

•	Object paths: Use the Object Paths command on the Chart menu to display the paths of solar system objects across the sky. The positions of objects along their paths can be marked and labeled with the date and time.

•	Lock command: The Lock command on the Animation menu allows you to lock the most recently selected or searched for solar system object to the center of the sky chart. You can also right-click on a solar system object and select the Lock command on the popup menu that appears.

•	Localized date and time formats: Local and universal dates can be entered and displayed in month/day/year, day/month/year, or year/month/day format, and local times can be entered and displayed in 12-hour or 24-hour format. The formats used are based on the preferences specified under Regional Settings in the Windows Control Panel.

•	Seasons Data dialog box: The Seasons Data dialog box, accessible from the Data menu, displays the local times, universal times, and Julian dates at which the four seasons of the year begin, as well as the duration of each season.

•	Twilight Data dialog box: The Twilight Data dialog box, accessible from the Data menu, displays the local times at which astronomical, nautical, and civil dawn and dusk begin and end, and the times at which sunrise and sunset occur. This data is displayed for the three previous days, the current day, and the three following days.

•	Lunar Phases Data dialog box: The Lunar Phases Data dialog box, accessible from the Data menu, displays the local times and Julian dates at the beginning of new moon, first quarter, full moon, and last quarter phases.

•	Copy buttons: The program's data dialog boxes contain Copy buttons that allow you to copy the data they display onto the clipboard. After the data has been copied onto the clipboard, it can be pasted into an editor or word processor, and then saved to a file or printed.

•	Popup menus: You can right-click on an object or point in the sky chart to display a popup menu. The menu may be used to move the object or point to the center of the sky chart, view data about the object, lock the object to the center of the sky chart, zoom in or out, or turn full screen mode on or off.

•	Angular separation display: You can display the angular separation between two points on the sky chart by using the mouse. To measure an angular separation, move the pointer over the first point, click and hold down the left mouse button, drag the pointer to the second point, and then release the mouse button. The angular separation will be displayed in the status bar until another message takes its place.


Updates

Changes introduced since the release of CyberSky 3.0 include:

CyberSky 3.1 (February 24, 2000)

•	Enhancement: Increased the speed at which stars, constellation figures, deep sky objects, and solar system objects are drawn. This is especially noticeable at high zoom levels. When only stars and solar system objects are displayed, animation at 32X is about five times faster than before. When locked on Jupiter, animation at 512X is about seven times faster than before. When locked on Saturn, animation at 4096X is about four times faster than before.

•	Enhancement: Added the Zodiacal only box to the Constellations dialog box, which allows only zodiacal constellation figures to be displayed.

•	Enhancement: Added the Copy button to the Planets Data dialog box, which allows the data displayed by this dialog box to be copied onto the clipboard, pasted into an editor or word processor, and then saved to a file or printed.

•	Correction: The equatorial coordinates at the center of the sky chart were not calculated correctly when horizon mode was turned on and the horizon was displayed. This was due to a bug in code that reverses the effects of atmospheric refraction. This caused a number of problems that became noticeable at very high zoom levels, especially when the viewpoint was near the horizon. Objects that should have been displayed were not displayed. Grids and lines were only partially displayed, or were not displayed at all. The equatorial coordinates displayed in the Pointer bar were not correct.

•	Correction: The lines that make up the constellation figures were sometimes not displayed correctly. This was due to a bug in code that performs line clipping, and occurred only at very high zoom levels.

•	Correction: The sun and moon were sometimes displayed when they were in fact not visible in the area of sky being displayed. This was due to a bug in code that converts equatorial coordinates to screen coordinates, and occurred only at very high zoom levels.

•	Correction: The dark parts of solar system object disks were not printed correctly. When the sky chart was printed in black and white, the dark parts of disks were not filled, which allowed objects, grids, and lines to be seen through them. When the sky chart was printed in color, the dark parts of disks were filled with the same colors used to fill the light parts, which caused the objects to always appear as if they were at full phase.

CyberSky 3.0.3 (October 14, 1999)

•	Enhancement: Added the Keyboard Shortcuts, Ordering Information, and Registration Benefits commands to the Help menu to make it easier to access the associated topics in the program's Help file.

•	Correction: The Save Bitmap command on the File menu was disabled if the program could not find an available printer at startup.

•	Correction: The popup menu that appeared when a Messier object fainter than magnitude 8.5 was right-clicked did not include an About command for that object. This made it impossible to display the Deep Sky Object Data dialog box for that object.

•	Modification: When the program starts up in horizon mode, it now displays the sky above the south horizon if the location is on or above the equator, or above the north horizon if the location is below the equator. Previously, the program always displayed the sky above the south horizon at startup.

•	Modification: When the animation time step is set to one or more years, the size of each step is now adjusted so that the year changes during animation but the month and day remain the same. Previously, the size of each step was constant, which caused the month and day to change during animation due to the addition of leap days to the calendar.

CyberSky 3.0.2 (July 29, 1999)

•	Correction: The Deep Sky Object Data dialog box did not correctly classify open clusters; they were instead classified as globular clusters.

CyberSky 3.0.1 (June 10, 1999)

•	Correction: The Left and Right commands did not scroll the sky chart correctly when atlas mode was turned on. The Left command scrolled the sky chart to the right rather than to the left, and the Right command scrolled the sky chart to the left rather than to the right.

•	Correction: A system resource leak occurred when the path of a solar system object was displayed with date or time labels. This caused the amount of free system resources to drop each time the sky chart was drawn. If this system resource leak continued, it eventually caused the program to stop functioning correctly.

•	Correction: The data displayed in the Seasons Data dialog box did not reflect the fact that the four seasons start at different times of the year in the Southern Hemisphere than they do in the Northern Hemisphere.


License agreement

This agreement is a legal contract that specifies the terms of the license and warranty limitation between you and Stephen Michael Schimpf for the CyberSky software and any related documentation. You should carefully read the following terms before using this software. Unless you have a different license agreement signed by Stephen Michael Schimpf, your use of this software indicates your acceptance of the terms of this agreement.

Copyright

CyberSky is owned by Stephen Michael Schimpf and is protected by United States copyright laws and international treaty provisions. Therefore, you must treat CyberSky like any other copyrighted material. CyberSky is licensed, not sold. All rights to the CyberSky software and any related documentation not expressly granted under this agreement are reserved by Stephen Michael Schimpf.

Registered version

If you have purchased the registered version of CyberSky, Stephen Michael Schimpf hereby grants you the following non-exclusive license:

You may use the registered version of CyberSky on one or more computers, provided the software is run on only one computer at any given time, or you have purchased licenses covering all computers that will run the software at the same time.

You may use the output of the registered version of CyberSky for noncommercial purposes, in both electronic and physical publications, provided you credit CyberSky as the source. You are encouraged to provide a link to www.cybersky.com.

You may make copies of the registered version of CyberSky for the sole purpose of backing up the software and protecting your investment from loss.

Shareware version

If you have obtained the shareware version of CyberSky, Stephen Michael Schimpf hereby grants you the following non-exclusive license:

You may use the shareware version of CyberSky free of charge on up to 21 separate days for the sole purpose of evaluating the software. Use of the software beyond this evaluation period requires that you purchase the registered version of CyberSky.

You may freely copy and redistribute the shareware version of CyberSky by electronic means and on physical media, provided it is distributed in its original, unmodified form, and that it is not sold for profit.

Termination

This license will terminate immediately if you fail to comply with any provision of this license.

Disclaimer of warranty

CYBERSKY IS SUPPLIED "AS IS" WITHOUT WARRANTY OF ANY KIND. TO THE MAXIMUM EXTENT PERMITTED BY APPLICABLE LAW, STEPHEN MICHAEL SCHIMPF DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. STEPHEN MICHAEL SCHIMPF'S LIABILITY WILL BE LIMITED EXCLUSIVELY TO PRODUCT REPLACEMENT OR REFUND OF PURCHASE PRICE.

BECAUSE SOME STATES AND JURISDICTIONS DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES, THE ABOVE LIMITATION MAY NOT APPLY TO YOU.

Governing law

If you acquired this product in the United States, this agreement is governed by the laws of the State of California.

If this product was acquired outside the United States, then local law may apply.


Save Bitmap command
Save Bitmap command (File menu)

Saves the sky chart as a bitmap file.

Shortcut

Press the Ctrl+B keys.


Print Setup command
Print Setup command (File menu)

Sets the printer and printing options.


Print Preview command
Print Preview command (File menu)

Displays a sky chart as it will look when printed.

Print Preview button

Click this button on the View toolbar to execute this command.


Print command
Print command (File menu)

Prints a sky chart. CyberSky prints sky charts in landscape orientation by default. Use the Print Setup command on the File menu to switch to portrait orientation. Use the Print Preview command on the File menu to display a sky chart as it will look when printed.

Print button

Click this button on the View toolbar to execute this command.

Shortcut

Press the Ctrl+P keys.


Exit command
Exit command (File menu)

Closes the application's window and exits the application.

Shortcut

Press the Alt+F4 keys.


Zoom In command
Zoom In command (View menu)

Displays the sky chart at a higher zoom level.

Zoom In button

Click this button on the View toolbar to execute this command.

Shortcut

Press the PgUp key.


Zoom Out command
Zoom Out command (View menu)

Displays the sky chart at a lower zoom level.

Zoom Out button

Click this button on the View toolbar to execute this command.

Shortcut

Press the PgDn key.


Zoom Level command
Zoom Level command (View menu)

Sets the zoom level for the sky chart.


North command
North command (View menu)

Displays the sky above the north horizon. Using this command sets the viewing azimuth to 0 degrees, the altitude to 45 degrees, and the zoom level to 2X.

North button

Click this button on the View toolbar to execute this command.

Shortcut

Press the N key.


East command
East command (View menu)

Displays the sky above the east horizon. Using this command sets the viewing azimuth to 90 degrees, the altitude to 45 degrees, and the zoom level to 2X.

East button

Click this button on the View toolbar to execute this command.

Shortcut

Press the E key.


South command
South command (View menu)

Displays the sky above the south horizon. Using this command sets the viewing azimuth to 180 degrees, the altitude to 45 degrees, and the zoom level to 2X.

South button

Click this button on the View toolbar to execute this command.

Shortcut

Press the S key.


West command
West command (View menu)

Displays the sky above the west horizon. Using this command sets the viewing azimuth to 270 degrees, the altitude to 45 degrees, and the zoom level to 2X.

West button

Click this button on the View toolbar to execute this command.

Shortcut

Press the W key.


Zenith command
Zenith command (View menu)

Displays the sky directly overhead. Using this command sets the viewing altitude to 90 degrees and the zoom level to 1X. The viewing altitude is not changed, making it possible to create a full sky view with any azimuth at the bottom of the display. For example, if you'd like to display a full sky view with the west point at the bottom of the display, first use the West command on the View menu to bring the west point to the bottom of the display. Then use the Zenith command to look up at the zenith.

Zenith button

Click this button on the View toolbar to execute this command.

Shortcut

Press the Z key.


Full Screen command
Full Screen command (View menu)

Turns full screen mode on or off.

Shortcut

Press the Ctrl+F keys.


View Toolbar command (View menu)

Displays or hides the View toolbar.


Time Toolbar command (View menu)

Displays or hides the Time toolbar.


Chart Toolbar command (View menu)

Displays or hides the Chart toolbar.


Search Toolbar command (View menu)

Displays or hides the Search toolbar.


Data Bar command (View menu)

Displays or hides the Data bar.


Status Bar command
Status Bar command (View menu)

Displays or hides the status bar.


Location command (Options menu)

Sets the location from which the sky is being viewed.


Return Home command (Options menu)

Sets the location to your home location.

Shortcut

Press the Ctrl+Home keys.


Daylight command (Options menu)

Turns daylight on or off. When daylight is turned on, the color of the sky background varies depending on the altitude of the sun. When daylight is turned off, the sky background remains the same color regardless of the altitude of the sun.

Shortcut

Press the Ctrl+D keys.


Colors command (Options menu)

Sets screen and printer colors.


Fonts command (Options menu)

Sets screen and printer fonts.


Atlas Mode command (Chart menu)

Turns atlas mode on. Turning atlas mode on causes lines of right ascension and declination to remain fixed when animation is used.

Shortcut

Press the Ctrl+A keys.


Horizon mode command (Chart menu)

Turns horizon mode on. Turning horizon mode on causes lines of azimuth and altitude to remain fixed when animation is used.

Shortcut

Press the Ctrl+Z keys.


Stars command (Chart menu)

Sets star display options.


Constellations command (Chart menu)

Sets constellation display options.


Deep Sky Objects command (Chart menu)

Sets deep sky object display options.


Solar System Objects command (Chart menu)

Sets solar system object display options.


Object Paths command (Chart menu)

Sets object path display options.


Grids command (Chart menu)

Sets grid display options.


Lines command (Chart menu)

Sets line display options.


Horizon command (Chart menu)

Displays or hides the horizon. When the horizon is displayed or hidden you may notice that the stars seem to move slightly. This is because atmospheric refraction corrections are performed when the horizon is displayed, but are not performed when the horizon is hidden.

Horizon button

Click this button on the Chart toolbar to execute this command.

Shortcut

Press the Ctrl+H keys.


Local Time command (Time menu)

Sets the local time at which the sky is being viewed.

Local Time button

Click this button on the Time toolbar to execute this command.

Shortcut

Press the Ctrl+L keys.


Universal Time command (Time menu)

Sets the universal time at which the sky is being viewed.

Shortcut

Press the Ctrl+U keys.


Julian Date command (Time menu)

Sets the Julian date at which the sky is being viewed.

Shortcut

Press the Ctrl+J keys.


Current Time command (Time menu)

Sets the local time to your computer's system time.

Use this command if you've changed the time or have used animation and would like to see how the sky looks at this moment.

Shortcut

Press the Ctrl+C keys.


Midnight command (Time menu)

Sets the local time to midnight.

Shortcut

Press the Ctrl+M keys.


Sunrise command (Time menu)

Sets the local time to sunrise.

Shortcut

Press the Ctrl+R keys.


Noon command (Time menu)

Sets the local time to noon.

Shortcut

Press the Ctrl+N keys.


Sunset command (Time menu)

Sets the local time to sunset.

Shortcut

Press the Ctrl+S keys.


Event command (Time menu)

Sets the local time to an object's rising, transiting, or setting time.

Shortcut

Press the Ctrl+E keys.


Equatorial Coordinates command (Search menu)

Searches for equatorial coordinates. This command displays a dialog box that allows you to enter the right ascension and declination to search for. The coordinates you search for will appear at the center of the display.


Horizontal Coordinates command (Search menu)

Searches for horizontal coordinates. This command displays a dialog box that allows you to enter the azimuth and altitude to search for. The coordinates you search for will appear at the center of the display.


Star command (Search menu)

Searches for a star. This command displays a dialog box that allows you to select a star to search for. The star you search for will appear at the center of the display. If you cannot see it, it may be below the horizon or may be too faint to see. Use the Horizon command on the View menu to display or hide the horizon, or click the Horizon button on the Chart toolbar. Use the Stars command on the Chart menu to change the limiting magnitude so that the star becomes visible at the center of the display.


Constellation command (Search menu)

Searches for a constellation. This command displays a dialog box that allows you to select a constellation to search for. The constellation you search for will appear at the center of the display. If you cannot see it, it may be below the horizon. Use the Horizon command on the View menu to display or hide the horizon, or click the Horizon button on the Chart toolbar.


Deep Sky Object command (Search menu)

Searches for a deep sky object. This command displays a dialog box that allows you to select an object to search for. The object you search for will appear at the center of the display. If you cannot see it, it may be below the horizon or may be too faint to see. Use the Horizon command on the View menu to display or hide the horizon, or click the Horizon button on the Chart toolbar. Use the Deep Sky Objects command on the Chart menu to change the limiting magnitude so that the object becomes visible at the center of the display.


Solar System Object command (Search menu)

Searches for a solar system object. This command displays a dialog box that allows you to select an object to search for. The object you search for will appear at the center of the display. If you cannot see it, it may be below the horizon. Use the Horizon command on the View menu to display or hide the horizon, or click the Horizon button on the Chart toolbar.

After you search for a solar system object, you can keep the object locked to the center of the display by using the Lock command on the Animation menu, clicking the Lock button on the toolbar, or right-clicking on the object and choosing the Lock command on the pop-up menu that appears.


Point command (Search menu)

Searches for a point. This command displays a dialog box that allows you to select a point to search for. The point you search for will appear at the center of the display. If you cannot see it, it may be below the horizon. Use the Horizon command on the View menu to display or hide the horizon, or click the Horizon button on the Chart toolbar.


Seasons command (Data menu)

Displays data about the seasons of the year.


Twilight command (Data menu)

Displays data about astronomical, nautical, and civil twilight.


Solar System Object command (Data menu)

Displays data about a solar system object.


Planets command (Data menu)

Displays data about all planets visible from the earth.


Lunar Phases command (Data menu)

Displays data about the phases of the moon.


Play Backward command (Animation menu)

Starts animation with time moving backward.

Play Backward button

Click this button on the Time toolbar to execute this command.

Shortcut

Press the < key.


Previous Step command (Animation menu)

Displays the previous animation step.

Previous Step button

Click this button on the Time toolbar to execute this command.

Shortcut

Press the [ key.


Stop command (Animation menu)

Stops animation.

Stop button

Click this button on the Time toolbar to execute this command.

Shortcut

Press the Esc key.


Next Step command (Animation menu)

Displays the next animation step.

Next Step button

Click this button on the Time toolbar to execute this command.

Shortcut

Press the ] key.


Play Forward command (Animation menu)

Starts animation with time moving forward.

Play Forward button

Click this button on the Time toolbar to execute this command.

Shortcut

Press the > key.


Time Step command (Animation menu)

Sets the animation time step.

Shortcut

Press the Ctrl+T keys.


Real Time command (Animation menu)

Turns real time mode on or off. Turning real time mode on causes the local time to be set to your computer's system time and causes the sky chart to be updated as quickly as possible so that it continues to match the real sky.

When real time mode is turned on, you cannot change the time or use the normal animation commands. These will all be disabled until you turn off real time mode.


Lock command (Animation menu)

Locks or unlocks a selected solar system object.

The lock feature is automatically turned on whenever you search for a solar system object, either by clicking one of the buttons on the Search toolbar or by using the Solar System Object command on the Search menu. A solar system object that has been locked will automatically be moved to the center of the sky chart whenever the time changes for any reason.

The lock feature is wonderful for watching various astronomical phenomena. To watch a solar eclipse, set the time a few hours before the eclipse begins, search for the sun, and then start animation. The sun will automatically be kept at the center of the sky chart, and you'll be able to watch the moon move across the sun's disk. You can use a similar procedure to watch the moon's disk move over a star and to watch the Galilean satellites of Jupiter move around that planet.

Lock button

Click this button to execute this command.

Shortcut

Press the Ctrl+K keys.


Help Topics command (Help menu)

Displays the application's Help topics.

Shortcut

Press the F1 key.


Keyboard Shortcuts command (Help menu)

Displays information about using keyboard shortcuts.


Ordering Information command (Help menu)

Displays information about ordering the registered version of CyberSky.


Registration Benefits command (Help menu)

Displays the benefits of ordering the registered version of CyberSky.


CyberSky Home Page command (Help menu)

Displays the CyberSky Home Page in your Web browser.


About CyberSky command (Help menu)

Displays the application's name, version number, and copyright notice.


Ordering information

You can order the registered version of CyberSky from shareware registration services located in the United States, Germany, and Australia, as well as directly from me, Stephen Michael Schimpf, the program's author. You can place your order by secure online order form, e-mail, phone, fax, and postal mail.

For your convenience, a variety of payment options are available, including payment by credit card, wire transfer, check, money order, and cash.

You can choose to download the software after your order is processed, to receive the software by e-mail attachment, or to have the software delivered to you on two 3.5-inch disks.

Please read the following ordering information carefully.

Pricing

Current prices, in US and Australian dollars, are as follows:

Single License                     US$  30    AU$  50

Site License ( 3 Computers)        US$  60    AU$ 100

Site License ( 5 Computers)        US$  90    AU$ 150

Site License (10 Computers)        US$ 120    AU$ 200

Site License (20 Computers)        US$ 180    AU$ 300

Site License (30 Computers)        US$ 240    AU$ 400

Site License (40 Computers)        US$ 300    AU$ 500

Upgrade License                    US$  20    AU$  30

Single, site, and upgrade licenses are defined as follows:

•	Single license
Purchasing a single license allows you to run the registered version of CyberSky on one or more computers, provided the software is run on only one computer at any given time. For example, if you would like to use CyberSky on your desktop computer as well as on a laptop that you take outside with you, you only need to purchase a single license.

•	Site license
Purchasing a site license allows you to run the registered version of CyberSky on multiple computers at one location. For example, if you would like to use CyberSky on a number of computers in a lab at a high school or college, you need to purchase a site license. Site license prices are based on the maximum number of computers on which you'll install CyberSky.

•	Upgrade license
Purchasing an upgrade license gives you the same benefits as purchasing a single license, but you must own a previous registered version of CyberSky to do so. For example, if you purchased version 1.0 or 2.0 in the past and now would like to upgrade to version 3.0, you only need to purchase an upgrade license.

Please send any questions you may have about pricing or these license definitions to sales@cybersky.com, or to Stephen Michael Schimpf, 2444 West 230th Street, Torrance, CA 90501-5242, USA.

Ordering from DigiBuy

You can make your payment by Visa, MasterCard, American Express, Discover, or check.

You can place your order in the following ways:

•	By secure online order form
Please use the following link:

Order Now! Online Delivery Available!

•	By phone
Please call 1-800-242-4775 ext. 14084 toll-free from within the United States, or +1-713-524-6394 ext. 14084 from outside the United States.

•	By fax
Please fill out the secure online order form, select the fax order option, and follow the instructions.

•	By postal mail
Please fill out the secure online order form, select the postal mail order option, and follow the instructions.

You can choose to download the software after your order is processed, or to have the software delivered to you on two 3.5-inch disks.

Ordering from ShareIt!

You can make your payment by Visa, MasterCard, American Express, Diners Club, wire transfer, check, or cash. Please make your check payable to "ShareIt! Inc." if you are sending it to the United States, or to "element 5 AG" if you are sending it to Germany.

You can place your order in the following ways:

•	By secure online order form
Please use the following link:

Order Now!

•	By e-mail
Please send your name, postal mail address, e-mail address, product description, quantity desired, and credit-card information to register@shareit.com.

•	By phone
Please call 1-800-903-4152 ext. 103285 toll-free from within the United States, or +49-221-2407279 ext. 103285 from outside the United States.

•	By fax
Please send your name, postal mail address, e-mail address, product description, quantity desired, and credit-card information to 1-724-850-8187 from within the United States, or to +49-221-2407278 from outside the United States.

•	By postal mail
Please send your name, postal mail address, e-mail address, product description, quantity desired, and credit-card information or payment to ShareIt! Inc., P.O. Box 844, Greensburg, PA 15601-0844, USA, or to ShareIt!, element 5 AG, Sachsenring 69, 50677 Cologne, Germany.

You'll have the software delivered to you on two 3.5-inch disks.

Ordering from Shareware-Australia

You can make your payment by Visa, MasterCard, American Express, Bankcard, check, or money order. Please make your check or money order payable to "Shareware-Australia".

You can place your order in the following ways:

•	By secure online order form
Please use the following link:

Order Now!

•	By e-mail
Please send your name, postal mail address, e-mail address, product description, quantity desired, delivery method desired, and credit-card information to sales@shareware-australia.com.

•	By phone
Please call (02) 9565-2339 from within Australia, or +61-2-9565-2339 from outside Australia.

•	By fax
Please send your name, postal mail address, e-mail address, product description, quantity desired, delivery method desired, and credit-card information to (02) 9565-2362 from within Australia, or to +61-2-9565-2362 from outside Australia.

•	By postal mail
Please send your name, postal mail address, e-mail address, product description, quantity desired, delivery method desired, and credit-card information or payment to Shareware-Australia, P.O. Box 1075, Maroubra, NSW 2035, Australia.

You can choose to receive the software by e-mail attachment, or to have the software delivered to you on two 3.5-inch disks.

Ordering from Stephen Michael Schimpf

You can make your payment by check or money order payable in US dollars drawn on a US bank, international postal money order payable in US dollars, or cash in US dollars. Please make your check or money order payable to "Stephen Michael Schimpf".

You can place your order in the following way:

•	By postal mail
Please send your name, postal mail address, e-mail address, product description, quantity desired, delivery method desired, and payment or receipt for your international postal money order to Stephen Michael Schimpf, 2444 West 230th Street, Torrance, CA 90501-5242, USA.

You can choose to receive the software by e-mail attachment, or to have the software delivered to you on two 3.5-inch disks.


Registration benefits

CyberSky is marketed as "shareware" and is available in two distinct versions:

Shareware version. The shareware version of CyberSky allows you to "try before you buy", so you can determine whether the software works correctly on your computer and with your printer, and whether it is useful to you.

The shareware version does not include the complete star and deep sky object data files, in order to conserve space, and to provide an additional incentive for you to purchase the registered version.

Registered version. The registered version of CyberSky is the complete, fully functional version of the software. The registered version does not display any registration reminder messages, includes the complete data files, and allows you to continue to use the software after your evaluation period has expired.

Here are some images that compare what's displayed by the registered version with what's displayed by the shareware version:

Registered Version	Shareware Version
Objects to 8.5 magnitude	Objects to 5.0 magnitude
80,179 stars	1,671 stars
472 deep sky objects	68 deep sky objects
The registered version includes about 50 times more stars and about seven times more deep sky objects than are included with the shareware version. As you can see, this additional data makes for much more attractive and useful sky charts.

When you purchase the registered version of CyberSky, you'll also receive the following benefits:

•	Product support. You'll receive product support for the lifetime of the product. In addition, I'll do my best to resolve any problems you report within 30 days of your purchase of the software. If I cannot resolve the issue to your satisfaction, I'll refund the full purchase price.

•	Free minor version updates. You'll be able to update the registered version of CyberSky to future minor version releases (3.0.1, 3.0.2, and so on) by using free patch files available from my Web site at www.cybersky.com.

•	Discounted major version upgrades. You'll be able to purchase upgrades to future major version releases (4.0, 5.0, and so on) at discounted prices.

If you decide not to order the registered version because it lacks one or more features you consider essential, please take a moment to let me know. Send your comments and suggestions to stephen@cybersky.com, or to Stephen Michael Schimpf, 2444 West 230th Street, Torrance, CA 90501-5242, USA. Be assured that all comments and suggestions are recorded and will shape future versions of CyberSky.


Pointer bar

The Pointer bar is initially displayed along the right side of the sky chart, below the Data bar. The panes in the Pointer bar display the equatorial coordinates, horizontal coordinates, and constellation under the mouse pointer. Click the equatorial or horizontal coordinates pane to turn the equatorial or horizontal coordinate system grid on or off, or the constellation pane to access the Constellations dialog box.

Use the Pointer Bar command on the View menu to display or hide the Pointer bar.

To turn a docked bar into a floating bar, move the pointer over the empty area around the bar's buttons, press and hold down the mouse button, and then drag the pointer away, toward the center of the sky chart. When the bar's outline has changed shape and is where you want it, release the mouse button.

To turn a floating bar into a docked bar, move the pointer over the bar's title bar, press and hold down the mouse button, and then drag the pointer to any edge of the sky chart. When the bar's outline has changed shape and is where you want it, release the mouse button.


Equatorial coordinates pane (Pointer bar)

This pane displays the equatorial coordinates -- right ascension and declination -- currently under the pointer.

Click this pane to display or hide the equatorial coordinate system grid lines.


Horizontal coordinates pane (Pointer bar)

This pane displays the horizontal coordinates -- azimuth and altitude -- currently under the pointer.

Click this pane to display or hide the horizontal coordinate system grid lines.


Constellation pane (Pointer bar)

This pane displays the constellation currently under the pointer.

Click this pane to quickly access the Constellations dialog box.


Search toolbar

The Search toolbar is initially displayed along the bottom of the sky chart, above the status bar and to the right of the Chart toolbar. It contains buttons with deal with searching for solar system objects.

Use the Search Toolbar command on the View menu to display or hide the Search toolbar.

To turn a docked toolbar into a floating toolbar, move the pointer over the empty area around the toolbar's buttons, press and hold down the mouse button, and then drag the pointer away, toward the center of the sky chart. When the toolbar's outline has changed shape and is where you want it, release the mouse button.

To turn a floating toolbar into a docked toolbar, move the pointer over the toolbar's title bar, press and hold down the mouse button, and then drag the pointer to any edge of the sky chart. When the toolbar's outline has changed shape and is where you want it, release the mouse button.

When you move the pointer over a toolbar button and wait a second you'll see the name of the button appear in a small ToolTip window. A short description of the button will also appear in the left part of the status bar.


Sun command (Search toolbar)

Use this command to search for the sun. The sky chart will be redrawn with the sun at the center. If the sun is not visible at the center of the sky chart, it may be below the horizon. In that case, click the [image] button on the Chart toolbar, use the Horizon command on the Chart menu, or press the Ctrl+H keys to hide the horizon and make the sun visible.

Sun button

Click this button on the Search toolbar to execute this command.


Moon command (Search toolbar)

Use this command to search for the moon. The sky chart will be redrawn with the moon at the center. If the moon is not visible at the center of the sky chart, it may be below the horizon. In that case, click the [image] button on the Chart toolbar, use the Horizon command on the Chart menu, or press the Ctrl+H keys to hide the horizon and make the moon visible.

Moon button

Click this button on the Search toolbar to execute this command.


Mercury command (Search toolbar)

Use this command to search for Mercury. The sky chart will be redrawn with the planet at the center. If the planet is not visible at the center of the sky chart, it may be below the horizon. In that case, click the [image] button on the Chart toolbar, use the Horizon command on the Chart menu, or press the Ctrl+H keys to hide the horizon and make the planet visible.

Mercury button

Click this button on the Search toolbar to execute this command.


Venus command (Search toolbar)

Use this command to search for Venus. The sky chart will be redrawn with the planet at the center. If the planet is not visible at the center of the sky chart, it may be below the horizon. In that case, click the [image] button on the Chart toolbar, use the Horizon command on the Chart menu, or press the Ctrl+H keys to hide the horizon and make the planet visible.

Venus button

Click this button on the Search toolbar to execute this command.


Mars command (Search toolbar)

Use this command to search for Mars. The sky chart will be redrawn with the planet at the center. If the planet is not visible at the center of the sky chart, it may be below the horizon. In that case, click the [image] button on the Chart toolbar, use the Horizon command on the Chart menu, or press the Ctrl+H keys to hide the horizon and make the planet visible.

Mars button

Click this button on the Search toolbar to execute this command.


Jupiter command (Search toolbar)

Use this command to search for Jupiter. The sky chart will be redrawn with the planet at the center. If the planet is not visible at the center of the sky chart, it may be below the horizon. In that case, click the [image] button on the Chart toolbar, use the Horizon command on the Chart menu, or press the Ctrl+H keys to hide the horizon and make the planet visible.

Jupiter button

Click this button on the Search toolbar to execute this command.


Saturn command (Search toolbar)

Use this command to search for Saturn. The sky chart will be redrawn with the planet at the center. If the planet is not visible at the center of the sky chart, it may be below the horizon. In that case, click the [image] button on the Chart toolbar, use the Horizon command on the Chart menu, or press the Ctrl+H keys to hide the horizon and make the planet visible.

Saturn button

Click this button on the Search toolbar to execute this command.


Uranus command (Search toolbar)

Use this command to search for Uranus. The sky chart will be redrawn with the planet at the center. If the planet is not visible at the center of the sky chart, it may be below the horizon. In that case, click the [image] button on the Chart toolbar, use the Horizon command on the Chart menu, or press the Ctrl+H keys to hide the horizon and make the planet visible.

Uranus button

Click this button on the Search toolbar to execute this command.


Neptune command (Search toolbar)

Use this command to search for Neptune. The sky chart will be redrawn with the planet at the center. If the planet is not visible at the center of the sky chart, it may be below the horizon. In that case, click the [image] button on the Chart toolbar, use the Horizon command on the Chart menu, or press the Ctrl+H keys to hide the horizon and make the planet visible.

Neptune button

Click this button on the Search toolbar to execute this command.


Pluto command (Search toolbar)

Use this command to search for Pluto. The sky chart will be redrawn with the planet at the center. If the planet is not visible at the center of the sky chart, it may be below the horizon. In that case, click the [image] button on the Chart toolbar, use the Horizon command on the Chart menu, or press the Ctrl+H keys to hide the horizon and make the planet visible.

Pluto button

Click this button on the Search toolbar to execute this command.


The sun

Overview | Interior | Surface | Atmosphere | Properties

Overview

The sun, a typical star of spectral type G2 and luminosity class V, is one of several hundreds of billions of stars that make up our galaxy, a spiral galaxy called the Milky Way. The sun and the rest of our solar system are located on the inner edge of a spiral arm, about 8,500 parsecs (28,000 light years) from the center of the Milky Way. The sun revolves around the galactic center once every 240 million years.

The sun is also the center of our solar system. The planets, asteroids, comets, and meteoroids all revolve around it. The solar system formed from an immense cloud of interstellar gas and dust about five billion years ago. The sun contains about 99.86 percent of all the mass in the solar system. The remaining 0.14 percent formed the other bodies of the solar system.

Like all stars, the sun is a globe of incandescent gas. Analysis of the spectrum of light we receive from the sun allows us to determine that it is made of about 92 percent hydrogen, 7 percent helium, and 1 percent other gases such as carbon, oxygen, nitrogen, and neon. In fact, helium was discovered in the atmosphere of the sun before it was discovered here on the earth.

Computer models indicate that the sun has been active for about five billion years, and will remain so for another five billion years. This value for the sun's age agrees with the ages measured for the planets, and suggests that the sun and its planetary system formed at the same time.

Interior

The sun's energy, which is necessary for life on this planet, originates in the sun's core. The temperature at the core is about 27 million Celsius (15 million Fahrenheit). At such high temperatures the nuclei of hydrogen atoms move at over 1000 kilometers (620 miles) per second and undergo many collisions with other nuclei. A very small percentage of these nuclei take part in reactions that result in four hydrogen nuclei fusing together to form one helium nucleus. The helium nucleus is 0.71 percent lighter than the four hydrogen nuclei, and this excess mass is converted into energy in the form of gamma rays.

The sun is in a state of equilibrium, meaning that for any given piece of the sun the pressure of the gases below just balance the weight of the gases above. To maintain its equilibrium, the sun must convert 600 million tons of hydrogen into helium every second, meaning that 4 million tons of mass are converted into energy every second.

Surrounding the core is a layer in which the energy generated in the core is transported outward by way of radiation. Surrounding this zone of radiative transport is another layer in which convection replaces radiation as the means by which energy moves to the surface. In this layer, warmer columns of solar material, called convective cells, move upward while cooler columns move downward. Such convective cells are typically 1000 kilometers (620 miles) in diameter, and are usually visible for five or 10 minutes before sinking below the photosphere. The energy generated in the sun's core spends over a million years traveling through the sun, first by radiation, then by convection, until it escapes into space.

The sun will not continue to shine indefinitely. When all of the hydrogen in the sun's core has been used up it will shrink and increase its temperature, while the sun's atmosphere will expand and the photosphere will become cooler. The conversion of hydrogen into helium will begin in a thin shell surrounding the core, causing the core to shrink and the outer layers of the sun to expand. After a period of adjustment the sun will continue to live as a red giant star for another billion years. Its atmosphere will expand until it swallows the inner planets. Finally, it will blow its atmosphere into space and the exposed core will remain as a type of star known as a white dwarf. Such is the fate of a star such as the sun. Stars that are much more massive than the sun end their lives as neutron stars or black holes.

Surface

The sun's "surface", called its photosphere, is the innermost layer of the sun that is opaque to visible light. The photosphere is only about 400 kilometers (250 miles) thick. It has a granulated appearance, due to the turbulent eruptions of convective cells when they reach the surface. The temperature in the photosphere is about 5,500 Celsius (9,950 Fahrenheit).

Sunspots are associated with strong magnetic fields in the photosphere. These fields disrupt the movement of convective cells and therefore cool a small region of the photosphere. Such regions are still very hot, having a temperature of about 4,000 Celsius (7,200 Fahrenheit), but appear darker in comparison to their surroundings. Most sunspots, which are irregular in shape and are typically about 10,000 kilometers (6,200 miles) in size, form and then disappear in only a week. But, larger ones may last for a month or longer, and can be observed to disappear from one limb only to reappear again a couple of weeks later on the opposite limb.

The number of sunspots on the photosphere varies with time, in cycles of roughly 11 years. The equatorial regions of the sun rotate in about 25 days, slightly faster than the polar regions which rotate in 30 days. Deeper regions of the sun appear to rotate in 27 days. It is this differential rotation that causes the subsurface magnetic field to build up and eventually burst through the photosphere, disrupting the normal flow of solar energy. Only a few sunspots may be observed at the minimum of the solar cycle, while more than 100 may be observed at maximum. The formation of so many sunspots releases the built-up magnetic energy, allowing another cycle to begin.

Atmosphere

The region above the sun's photosphere is called the chromosphere. The chromosphere extends about 10,000 kilometers (6,200 miles) above the photosphere. It is here where absorption lines are produced in the sun's spectrum.

Flares are short-lived phenomena that arise in the chromosphere. They are filaments of hot gas that emerge from regions that contain sunspots. Flares typically shoot away from the sun at about 200 kilometers (120 miles) per second. Energetic flares can produce aurorae in our atmosphere and can interfere with terrestrial communication.

The outer region of the sun, extended far above the chromosphere, is the corona. The corona is the halo of light that appears around the sun during a total solar eclipse. The corona's density is very low, but its effective temperature is very high, well over 1,000,000 Celsius (1,800,000 Fahrenheit).

Prominences arise in the corona. Prominences are immense arcs of ionized gas that streak out into space above the surface of the sun. Such prominences occur when the ionized gas escapes the confines of the sun's low-level magnetic field.

The particles that make up the corona escape the sun, continuously flowing outward through the solar system. This outflow, known as the solar wind, interacts with the magnetic fields of planets and is also responsible for the light displays we call aurorae.

Properties

Distance from the earth	147.0 to 152.0 million kilometers

91.34 to 94.45 million miles

0.983 to 1.016 astronomical units

Absolute magnitude	4.8

Diameter	1,392,000 kilometers

864,900 miles

109.1 times that of the earth

Rotation period	25.04 days

Average density	1.41 grams per cubic centimeter

Surface gravity	27.90 times that of the earth

Surface temperature	5,780 K

5,500 C

9,950 F

Escape velocity	618 kilometers per second

384 miles per second


The moon

Overview | Interior | Surface | Atmosphere | Properties

Overview

The moon is occasionally referred to as Luna or Selene after goddesses in Roman and Greek mythology, but is usually just called "the moon".

Other than the sun, the moon is the only celestial object that appears as a disk to the naked eye. When Galileo observed the moon with his crude telescope in 1610 he saw that its surface is rugged and mountainous, and this fact lead to the moon and planets being considered as other worlds.

Interior

During the Apollo moon landings, astronauts set up seismic monitoring stations to measure the waves generated by moonquakes and by meteoroid impacts. The study of the propagation of those waves tells us that the moon's interior is stratified, or layered, similar to the earth's interior.

The center of the moon consists of a small core made of rock. Unlike the earth's core, the moon's core is not metallic. The core is surrounded by a mantle, which may be hot enough to be partially molten. The energy to heat the mantle comes from the decay of radioactive elements found within it. The mantle in turn is surrounded by a crust. The moon has a relatively substantial crust, on average about 60 kilometers (37 miles) thick.

Surface

The surface of the moon consists of two types of terrain. The lighter parts of the surface are called the highlands. This terrain is rugged and is covered in craters of all sizes. The darker parts, called maria, are smoother with many small craters but relatively few large ones. The lunar highlands are about 4 billion years old, whereas the lunar maria are about 3.2 billion years old.

About four billion years ago the moon was bombarded by asteroids and meteoroids, matter that was left over from the formation of the solar system. This bombardment resulted in millions of impact craters of all sizes, including basins hundreds of kilometers across.

After this period of intense bombardment, heat created by the decay of radioactive elements melted the lunar rock hundreds of kilometers below the surface. This lava rose to the surface and filled the impact basins, creating the dark areas we call the lunar maria, or "seas". These lava flows are only a few hundred meters (about a thousand feet) thick. The maria cover about 16 percent of the lunar surface, and of the 30 known maria all but 4 are located on the moon's near side.

Pictures of either type of terrain reveal more craters than the eye can count. Large craters are filled with smaller craters, and those smaller craters are filled with even smaller craters. The reason for the abundance of craters on the moon's surface is simply that the body lacks an atmosphere. In the absence of rain and wind craters are not eroded.

Atmosphere

The moon does not have an atmosphere. Rare instances of gases escaping from the moon's interior have been observed, but these gases are quickly lost to space. The moon is not massive enough to maintain an atmosphere.

Properties

Distance from the earth	363,260 to 405,540 kilometers

225,720 to 251,990 miles

Sidereal period	27.3217 days

Synodic period	29.5306 days

Rotation period	29.5306 days

Eccentricity of orbit	0.055

Inclination of orbit	5.1 degrees

Inclination of axis	6.7 degrees

Average velocity	1.0 kilometers per second

0.62 miles per second

Mass	0.0123 times that of the earth

Diameter	3,476 kilometers

2,160 miles

0.272 times that of the earth

Average density	3.34 grams per cubic centimeter

Surface gravity	0.17 times that of the earth

Albedo	0.07

Surface temperature	100 to 400 K

-173 to 127 C

-279 to 261 F

Escape velocity	2.4 kilometers per second

1.5 mile per second


Mercury

Overview | Interior | Surface | Atmosphere | Rings | Moons | Properties

Overview

Mercury is the planet closest to the sun. It is named after the messenger of the gods in Roman mythology, know as Hermes in Greek mythology.

Mercury is visible without optical aid and has therefore been known since ancient times. Mercury is the most difficult of the naked-eye planets to observe, because it is always within 28 degrees of the sun and is therefore usually lost in its glare. It can only be seen under favorable conditions at dusk or dawn when it is low on the horizon and our view of it is poor.

Next to Pluto, Mercury has the highest orbital eccentricity and inclination of any planet in our solar system. Because Mercury's orbit lies inside that of the earth, its disk shows phases varying from full at superior conjunction to new at inferior conjunction. Mercury occasionally passes in front of the sun's disk. The next time this will happen is in November 1999.

Interior

Although Mercury resembles the moon in many ways, the planet's interior composition is very different. Whereas the moon is composed mostly of rock, Mercury appears to be composed of a core of iron and nickel about the size of the moon, covered by a layer of rock. The planet's outer layer consists of light silicate rock like the earth's mantle.

Mercury has a weak magnetic field, only about 1 percent as strong as the earth's.

Surface

Mercury's surface resembles that of the moon, in that it is heavily scarred by impact craters, but it is more complex. At least a dozen types of terrain have been identified. Surface features are generally named after musicians, painters, poets, and writers. The largest impact feature is the Caloris Basin, which is about 1,300 kilometers (810 miles) in diameter. The next largest feature is the crater Beethoven, 625 kilometers (388 miles) in diameter. The number of craters per unit surface area can be as high as that on the moon, but there are no regions of relative smoothness similar to the lunar maria.

Although Mercury does not show signs of the type of volcanic activity that produced the lunar maria, the planet has experienced volcanism. It also shows other signs of geologic activity. In the distant past Mercury's interior apparently shrunk, compressing the planet's crust and resulting in lines of cliffs, called lobate scarps, that have no counterpart on the surface of the moon. These cliffs are up to 3 kilometers (1.9 miles) high and 500 kilometers (310 miles) long.

Temperatures range from 427 Celsius (801 Fahrenheit) on the daytime side to about -173 Celsius (-279 Fahrenheit) on the nighttime side.

Atmosphere

Mercury has essentially no atmosphere, although traces of hydrogen, helium, sodium, and potassium have been detected. Hydrogen and helium are brought to Mercury by the solar wind whereas sodium and potassium are released from within the planet's interior. Mercury's gravity is not strong enough to retain an atmosphere, and its high surface temperature further accelerates the escape of gases into space.

Rings

Mercury does not have any rings.

Moons

Mercury does not have any moons.

Properties

Distance from the sun	45.9 to 69.7 million kilometers

28.5 to 43.3 million miles

0.307 to 0.466 astronomical units

Sidereal period	0.241 years

87.969 days

Synodic period	115.88 days

Rotation period	58.65 days

Eccentricity of orbit	0.2056

Inclination of orbit	7.00 degrees

Inclination of axis	0.0 degrees

Average velocity	47.89 kilometers per second

29.76 miles per second

Mass	0.0553 times that of the earth

Volume	0.0562 times that of the earth

Diameter	4,877 kilometers

3,030 miles

0.382 times that of the earth

Average density	5.43 grams per cubic centimeter

Surface gravity	0.38 times that of the earth

Albedo	0.056

Surface temperature	100 to 700 K

-173 to 427 C

-279 to 801 F

Escape velocity	4 kilometers per second

2.5 miles per second


Venus

Overview | Interior | Surface | Atmosphere | Rings | Moons | Properties

Overview

Venus is the second planet from the sun and the closest inferior planet to the earth. It is named after the goddess of beauty and love in Roman mythology, known as Aphrodite in Greek mythology. The Greeks regarded Venus as two separate objects: Phosphorus, the Morning Star, and Hesperus, the Evening Star.

Venus is visible without optical aid and has therefore been known since ancient times. In fact, other than the sun and the moon, Venus is the brightest object in the sky. Because the orbit of Venus lies inside that of the earth, it's disk shows phases varying from full at superior conjunction to new at inferior conjunction. Venus rotates in the retrograde direction, meaning that the sun rises in the west and sets in the east. Like Mercury, Venus occasionally passes in front of the sun's disk. The next time this will happen is in 2004.

It resembles the earth in composition, density, and size more closely than any other planet, and has therefore sometimes been referred to as the earth's twin. Although the earth and Venus share many features, the two planets also differ in significant ways. Conditions on the surface of Venus and in its atmosphere are extremely hostile.

Interior

Venus has a core of nickel and iron, similar to that of the earth. Venus has a very weak magnetic field, which suggests that it slow rotation rate is not fast enough to generate a more substantial magnetic field.

Surface

The surface of Venus is generally smoother than the surface of the earth. All but a few of the surface features are named after women.

Volcanoes are abundant on Venus, and appear to be the dominant force that shaped the planet's surface. Lowlands and highlands account for about 20 percent of the terrain, and the remaining 80 percent consists of lava plains similar to the maria on the surface of the moon.

About 1000 impact craters have been detected on Venus. None of them are smaller than about 2 kilometers (1.2 miles) in diameter, thanks to the protective effect of the planet's atmosphere. Meteoroids that would product craters smaller than this size do not survive the passage through the atmosphere.

Venus is the hottest planet in the solar system. The surface temperature on Venus is about 427 Celsius (801 Fahrenheit), and is nearly constant over the entire planet.

Atmosphere

The Venusian atmosphere consists of about 96 percent carbon dioxide, 3 percent nitrogen, and 1 percent other gases such as helium, neon, and argon. It is very dense, resulting in an atmospheric pressure at the surface about 97 times that of the earth's atmosphere.

Unlike the earth, Venus is completely covered by a layer of clouds about 30 kilometers (18.6 miles) thick. These clouds are excellent reflectors of sunlight, giving Venus the highest albedo of any planet in the solar system. At least three distinct cloud layers have been detected. The lowest layer appears to be predominantly composed of sulfur particles, whereas the upper layer is composed of sulfuric acid droplets.

Although the clouds reflect about 76 percent of the sunlight that falls on them, a small fraction of visible light reaches the surface. This energy is radiated from the surface in the form of infrared radiation. Whereas carbon dioxide is transparent to visible light, this gas is opaque to infrared radiation The carbon dioxide in the atmosphere therefore acts like a greenhouse, letting light reach the surface but preventing it from being radiated back into space. This is the reason why Venus is so very hot.

Rings

Venus does not have any rings.

Moons

Venus does not have any moons.

Properties

Distance from the sun	107.4 to 109.0 million kilometers

66.74 to 67.73 million miles

0.718 to 0.729 astronomical units

Sidereal period	0.615 years

224.701 days

Synodic period	583.92 days

Rotation period	243.0 days

Eccentricity of orbit	0.0068

Inclination of orbit	3.39 degrees

Inclination of axis	177.4 degrees

Average velocity	35.03 kilometers per second

21.77 miles per second

Mass	0.815 times that of the earth

Volume	0.857 times that of the earth

Diameter	12,104 kilometers

7,521 miles

0.949 times that of the earth

Average density	5.24 grams per cubic centimeter

Surface gravity	0.91 times that of the earth

Albedo	0.72

Surface temperature	700 K

427 C

801 F

Escape velocity	10 kilometers per second

6.2 miles per second


The earth

Overview | Interior | Surface | Atmosphere | Rings | Moons | Properties

Overview

The earth is the third planet from the sun, and the only one on which we know there is life. The earth is also the only planet on which we know there is liquid water, and which has an atmosphere and surface conditions suitable for life as we know it.

Interior

The study of the propagation of earthquake waves tells us that the earth's interior is stratified, or layered.

The very center of our planet consists of a solid inner core, made of iron, about 2,400 kilometers (1,500 miles) in diameter. Surrounding this is a layer of iron, nickel, and sulfur in molten form about 4,600 kilometers (2,900 miles) thick. It is the rotation and turbulent convection of material in this liquid outer core that generates our planet's magnetic field. We are lucky that this is so, because the magnetic field protects us from the sun's harmful radiation.

The earth's core is surrounded by a mantle of minerals heated by the core below and the decay of radioactive elements within it.

Surrounding the mantle is a relatively thin layer called the crust. The oceanic crust is made of basalt rocks and is on average 6 kilometers (3.7 miles) thick. The continental crust is made of granite rocks and varies in thickness from about 20 kilometers (12.4 miles) to about 70 kilometers (43.5 miles).

Surface

The earth's surface is shaped by the forces of plate tectonics. The earth's crust is organized into six major and ten minor plates that move over the mantle. Regions where two plates are pulling apart are called rift zones. Molten lava moves upward from the mantle to create new crust between these plates. It is the upward flow of lava in these regions that drives the slow motion of the plates. A good example of such a zone is the Mid-Atlantic Ridge.

Subduction zones are regions were one plate is being forced under another, and crust is being destroyed when it is pulled down into the earth's mantle. Regions where two plates collide but neither is forced under result in the formation of mountains such as the Himalayas. It is also possible for two plates to slide past each other. Such a region is called a fault, and a good example is the San Andreas fault responsible for earthquakes in California.

Although the earth is slightly larger than Venus, the latter planet actually has a much larger land surface because about 70 percent of our planet's crust is covered by water. The earth's land area is distributed among six large continents that rise out of the oceans.

One of the most obvious differences between the earth's surface and the surface of our neighbors in space is the lack of impact craters. When the earth was a young planet it was bombarded by meteoroids just like the other planets and moons were, but craters on this planet are destroyed quickly by the effects of plate tectonics and erosion due to rain and wind.

We do have evidence of relatively recent impact events. On June 30, 1908 the area near Tunguska, Siberia was struck by a meteoroid perhaps 60 meters (200 feet) in diameter. Despite the incredible devastation caused to animal and plant life in the area, this impact left no crater. About 50,000 years ago an impact in northern Arizona left a crater about 1.3 kilometers (0.8 miles) wide and 200 meters (660 feet) deep. This impact was caused by a body with a mass of about 100,000 tons.

Certainly the most spectacular impact, and the one most important for the eventual evolution of our species, took place about 65 million years ago. An asteroid about 15 kilometers (9.3 miles) in diameter struck the Yucatan peninsula in Mexico, creating a crater perhaps 200 kilometers (125 miles) across. The effect of this impact on the earth's atmosphere resulted in mass extinctions that destroyed most forms of life on this planet, including the dinosaurs.

Atmosphere

The atmosphere of the earth consists of 78 percent nitrogen, 21 percent oxygen, and 1 percent other gases such as argon and carbon dioxide. The average surface temperature is about 25 Celsius (16 Fahrenheit) warmer than it would be without the presence of carbon dioxide. This gas is responsible for a slight warming of our atmosphere by a process, called the greenhouse effect, that prevents some of the earth's heat being radiated into space.

The earth is unusual in that so much oxygen is found in the atmosphere instead of being trapped in minerals in surface rocks. The large percentage of oxygen in our atmosphere is due to green plants that manufacture oxygen out of carbon dioxide and water. Life could not have developed in our present oxygen-rich atmosphere, but evolved to take advantage of the gas when it grew abundant half a billion years ago. Animals now use this oxygen for respiration, and release carbon dioxide back into the air to be used by plants.

Rings

The earth does not have any rings.

Moons

The earth has one moon, occasionally referred to as Luna or Selene after goddesses in Roman and Greek mythology, but usually just called "the moon".

Properties

Distance from the sun	147.0 to 152.0 million kilometers

91.34 to 94.45 million miles

0.983 to 1.016 astronomical units

Sidereal period	1 year

365.24219 days

Rotation period	1.00 days

Eccentricity of orbit	0.017

Inclination of orbit	0.00 degrees

Inclination of axis	23.5 degrees

Average velocity	29.79 kilometers per second

18.51 miles per second

Mass	1.0 times that of the earth

Diameter	12,756 kilometers

7,926 miles

Average density	5.52 grams per cubic centimeter

Albedo	0.40

Surface temperature	250 to 300 K

-23 to 27 C

-9 to 81 F

Escape velocity	11 kilometers per second

6.8 miles per second


Mars

Overview | Interior | Surface | Atmosphere | Rings | Moons | Properties

Overview

Mars is the fourth planet from the sun and the closest superior planet to the earth. It is named after the god of war in Roman mythology, known as Ares in Greek mythology.

Mars is visible without optical aid and has therefore been known since ancient times. Mars sometimes appears brighter than Jupiter, and is characterized by its strong red color. Seen through a telescope, Mars does exhibit phases from gibbous to full at opposition.

Although Venus resembles the earth in composition, density, and size more closely than any other planet, surface conditions are far less hostile on Mars than they are on Venus. Mars has therefore been considered the prime candidate for harboring extraterrestrial life. Although the idea of Martian civilization was abandoned long ago, the possibility that primitive life of some sort existed there in the past cannot be ruled out. This topic has recently been in the news due to the discovery of what may be microscopic fossils in meteorites known to come from Mars.

Interior

Mars has a small core composed of iron sulfide, surrounded by a mantle of rock. The core apparently cooled and solidified in the past. Therefore, even though Mars possesses a metal core, the planet's rotation does not generate a substantial magnetic field. Mars has a relatively thin crust.

Surface

Mars is intermediate in size between the earth and the moon. Although Mars is smaller than the earth, it doesn't have any oceans and its land area is about equal to the area of the earth's continents. The rocks are rich in oxidized iron, which gives the surface its red color. The surface temperature varies between about -30 Celsius (-22 Fahrenheit) during the day and about -100 Celsius (-148 Fahrenheit) at night.

One mysterious aspect of the planet's surface is that the characters of the northern and southern hemispheres are fundamentally different. The surface of the northern hemisphere appears to be much younger than that of the southern hemisphere, and features volcanoes, extensive lava plains, and canyons, but relatively few impact craters. The surface of the southern hemisphere is older and is heavily cratered.

The main areas of volcanic activity are both located in the planet's northern hemisphere and are called the Tharsis Ridge and Elysium Planitia. The Tharsis Ridge contains the four largest volcanoes of Mars, named Olympus Mons, Ascraeus Mons, Pavonis Mons, and Arsia Mons. Olympus Mons is in fact the largest volcano in our solar system, rising about 25 kilometers (16 miles) above the surrounding plain. This volcano has a diameter of 700 kilometers (435 miles), and its caldera is 80 kilometers (50 miles) across. The principle volcano in Elysium Planitia is named Elysium Mons.

Counting the number of impact craters on the slopes of the volcanoes allows us to estimate the ages of the Tharsis Ridge volcanoes at between 200 million years and 800 million years. Those of Elysium Planitia appear to have ages of about 1,500 million years.

The surface of the southern hemisphere, which contains significantly more craters than the northern hemisphere, appears to be about 3.5 billion years old. Martian impact basins are also found here, with names such as Hellas, Isidis, and Argyre.

The craters of Mars are generally named after scientists. They closely resemble those found on the surface of the moons, but the material flung out beyond their rims looks different. These ejecta blankets appear to have run along the surface rather than falling from the sky after the meteoroid's impact. Apparently such impacts melted a significant amount of frozen water held in the planet's crust, resulting in the flow of material away from the craters. Many of the Martian craters appear to be eroded by blowing dust.

The equatorial region features a complex canyon system called the Valles Marineris, measuring 4,500 kilometers (2,800 miles) long from east to west and as much as 700 kilometers (430 miles) wide from north to south. Individual canyons are 200 kilometers (120 miles) wide and 7 kilometers (4 miles) deep. Although present atmospheric conditions don't permit rain or surface water to exist, some of the smaller surface features called channels appear to have been formed by running water. This suggests that in the past Mars may have had a denser atmosphere and milder climatic conditions.

The Martian year is nearly twice as long as a terrestrial year. The planet's axis of rotation is tilted to nearly the same angle as the earth's, and therefore Mars experiences the same type of seasons, although each season lasts nearly twice as long.

The north and south poles are covered by polar caps that vary in size throughout the Martian year. The seasonal polar caps are made of carbon dioxide ice and increase in size as carbon dioxide freezes out of the atmosphere during winter. They retreat during summer to reveal permanent polar caps made mostly of water ice. The seasonal polar caps appear to be only a few centimeters (about one inch) to perhaps one meter (three feet) thick. The permanent polar caps may be several kilometers (one or two miles) thick.

Atmosphere

The atmosphere of Mars, like that of Venus, is composed mostly of carbon dioxide. More precisely, it consists of about 95 percent carbon dioxide, 3 percent nitrogen, and 2 percent argon. Other gases exist in small proportions. But, whereas Venus has an atmosphere about 100 times denser than the earth's, Mars has an atmosphere about 100 times thinner. As was mentioned above, this atmospheric pressure is not high enough to permit liquid water to exist on the surface.

Winds on the surface are usually light, but during summer in the southern hemisphere strong seasonal winds blow fine dust as high as 25 kilometers (16 miles) into the atmosphere. These dust storms can engulf the entire planet and make it impossible to see surface features. It takes as much as six months for the dust to settle and conditions to return to normal. The variations in albedo causes by the deposition of dust are responsible for the charges in surface appearance that were once thought to indicate the presence of Martian vegetation.

Although only a small amount of water vapor exists in the atmosphere, the relative humidity is very high, meaning the atmosphere contains about as much water vapor as it can hold. We therefore frequently see this water vapor condense to create clouds around the planet's giant volcanoes and morning fog in the canyons and valleys.

Rings

Mars does not have any rings.

Moons

Mars has two moons, named Phobos and Deimos. Both were discovered in 1877 by Asaph Hall (1829-1907). Both are small and irregular in shape, and appear to be asteroids that were captured by Mars. Phobos and Deimos are faint objects, and can only be seen with large telescopes.

Properties

Distance from the sun	206.7 to 249.1 million kilometers

128.4 to 154.8 million miles

1.382 to 1.665 astronomical units

Sidereal period	1.881 years

686.98 days

Synodic period	779.94 days

Rotation period	1.03 days

Eccentricity of orbit	0.093

Inclination of orbit	1.85 degrees

Inclination of axis	25.2 degrees

Average velocity	24.13 kilometers per second

14.99 miles per second

Mass	0.107 times that of the earth

Volume	0.151 times that of the earth

Diameter	6,794 kilometers

4,222 miles

0.533 times that of the earth

Average density	3.94 grams per cubic centimeter

Surface gravity	0.39 times that of the earth

Albedo	0.16

Surface temperature	173 to 243 K

-100 to -30 C

-148 to -22 F

Escape velocity	5 kilometers per second

3.1 miles per second


Jupiter

Overview | Interior | Surface | Atmosphere | Rings | Moons | Properties

Overview

Jupiter is the fifth planet from the sun and the innermost of the "gas giants". It is the largest and most massive planet in the solar system. It is named after the ruler of the gods in Roman mythology, known as Zeus in Greek mythology.

Jupiter is visible without optical aid and has therefore been known since ancient times. It appears as a bright yellow "star" in the sky, and is only surpassed by Venus and occasionally Mars in brightness.

If Jupiter were about five dozen times more massive than it is, it could potentially evolve into a star. Jupiter would not be any larger than it is now, but its material would be far more compressed and its internal temperature would allow thermonuclear fusion to take place.

Interior

Unlike the terrestrial planets, the gas giants are essentially spheres of liquid hydrogen and helium, covered in an atmosphere of hydrogen and helium gas.

Jupiter's core may be made of rock and ice and may be 10 or 20 times as massive as the earth. Surrounding this core is an enormous ocean of liquid hydrogen. Deep inside Jupiter, under a pressure 3 million times that of the earth's atmosphere, the liquid hydrogen takes on the properties of a metal.

Thanks to the dynamo effect of this large rotating sphere of metallic hydrogen, Jupiter has a strong magnetic field, about 19,000 times as strong as that of the earth. Jupiter's magnetic field is tilted about 11 degrees with respect to its axis of rotation.

Jupiter radiates about twice as much energy as it receives from the sun, in the form of infrared light. The source of this energy is the reservoir of heat accumulated when Jupiter contracted from a cloud of gas and dust into the planet we see today.

Surface

Jupiter doesn't have a surface in the sense that the terrestrial planets do. Someplace deep inside Jupiter the thick atmosphere merges into a liquid.

Atmosphere

The atmosphere of Jupiter consists of approximately 86 percent hydrogen and 14 percent helium, with other gases present in very small percentages.

Jupiter's atmosphere is characterized by bands of brown, orange, white, and yellow clouds running parallel to the planet's equator. The light clouds are called zones and the dark clouds are called belts.

The upper cloud layer is composed of ammonia ice crystals, which gives these clouds their white appearance. Clouds further down in the atmosphere seem to contain compounds of sulfur and phosphorus, which gives them their brown, orange, and yellow coloration. Even deeper inside Jupiter's atmosphere we expect to find clouds composed of water vapor and ammonia.

The Great Red Spot, which is more than twice the size of the earth, appears to be the top of a rotating storm system in Jupiter's atmosphere. The Great Red Spot rotates counterclockwise about every 6 days. It was first reported by the English astronomer Robert Hooke in 1664. This feature has changed its color and size over time, and has temporarily disappeared from view, but has been the most prominent feature on Jupiter's disk for over a century and a half.

Rings

Jupiter has a single ring, discovered by the Voyager 1 spacecraft in 1979. Jupiter's ring has a very low albedo because it is made of grains of silicate dust that don't reflect sunlight very well. The ring lies about 54,000 kilometers (33,500 miles) from the planet and is about 5,000 kilometers (3,100 miles) wide.

Moons

Jupiter has 16 moons, named Metis, Adrastea, Amalthea, Thebe, Io, Europa, Ganymede, Callisto, Leda, Himalia, Lysithea, Elara, Ananke, Carme, Pasiphae, and Sinope.

Jupiter's four largest moons were discovered by Galileo Galilei (1564-1642) when he observed the planet through his telescope in 1610. These moons are easily visible through good binoculars, appearing as four "stars" near the planet. These Galilean satellites are respectable worlds in their own right. Jupiter's other moons are much smaller, and some may be captured asteroids.

Properties

Distance from the sun	740.9 to 815.7 million kilometers

460.4 to 506.9 million miles

4.953 to 5.453 astronomical units

Sidereal period	11.862 years

4,332.589 days

Synodic period	398.88 days

Rotation period	0.41 days

Eccentricity of orbit	0.04839

Inclination of orbit	1.305 degrees

Inclination of axis	3.12 degrees

Average velocity	13.06 kilometers per second

8.115 miles per second

Mass	317.83 times that of the earth

Volume	1,321.33 times that of the earth

Diameter	142,984 kilometers

88,846 miles

11.209 times that of the earth

Average density	1.33 grams per cubic centimeter

Surface gravity	2.54 times that of the earth

Albedo	0.70

Atmospheric temperature	110 to 150 K

-163 to -123 C

-261 to -189 F

Escape velocity	60 kilometers per second

37 miles per second


Saturn

Overview | Interior | Surface | Atmosphere | Rings | Moons | Properties

Overview

Saturn is the sixth planet from the sun, and the second largest planet in the solar system. It is named after the god of agriculture in Roman mythology, known as Cronus in Greek mythology.

Saturn is visible without optical aid and has therefore been known since ancient times. It is not as brilliant as the other naked-eye planets, and at best resembles a bright star.

Interior

Saturn is composed of the same elements as Jupiter. Like Jupiter, Saturn's core may be made of rock and ice and may be 10 or 20 times as massive as the earth.

Saturn possesses a strong magnetic field, although it is far weaker than that of Jupiter. It is still about 1000 times stronger than the earth's magnetic field.

Saturn radiates about three times as much energy as it absorbs from the sun. The source of energy for Jupiter's infrared emissions, energy from the planet's gravitational contraction billions of years ago, cannot account for Saturn's emissions. Saturn is simply not massive enough to have generated and stored this much energy. Nevertheless, the source of its energy does in fact come from gravitational energy. Saturn's interior is colder than Jupiter's and helium does not readily dissolve in this cold ocean of liquid hydrogen. Droplets of liquid helium form and slowly fall like rain toward the planet's core. The gravitational energy of these falling droplets is converted into heat and eventually radiated as infrared light.

Surface

Saturn doesn't have a surface in the sense that the terrestrial planets do. Someplace deep inside Saturn the thick atmosphere merges into a liquid.

Atmosphere

The atmosphere of Saturn consists of approximately 92 percent hydrogen and 8 percent helium, with other gases present in very small percentages.

Saturn's atmosphere, like Jupiter's, is characterized by bands of colorful clouds running parallel to the planet's equator. The light clouds are called zones and the dark clouds are called belts. These bands are less prominent than the conspicuous ones seen on Jupiter. Features observed in the atmosphere include clouds and a red oval that is similar to but smaller than Jupiter's Great Red Spot.

One surprising discovery about Saturn's atmosphere is the measurement of wind speeds near 1,500 kilometers (930 miles) per hour. These wind speeds are about five times as high as those measured on Jupiter.

Rings

Although Galileo Galilei (1564-1642) was the first person to observe Saturn through a telescope, he did not recognize the nature of what he saw. The Dutch astronomer Christiaan Huygens (1629-1695) first realized that Saturn was surrounded by rings in 1659.

Saturn's rings lie between 7,000 kilometers (4,300 miles) and 100,000 kilometers (62,000 miles) above the planet's cloud tops. Seen from the earth, Saturn appears to have six rings, but photographs taken by spacecraft have revealed each of these rings to be composed of hundreds of thin rings with intervening spaces. Altogether Saturn has at least a thousand rings. Remarkably, the ring system is only about 20 meters (66 feet) thick!

Unlike the rings of Jupiter, which are composed of tiny grains of dark silicate dust, the rings of Saturn are made of bright water ice particles which range in size from small grains up through large boulders. Most of the particles are several centimeters (about one inch) in size.

Moons

Saturn has 18 moons, named Pan, Atlas, Prometheus, Pandora, Janus, Epimetheus, Mimas, Enceladus, Tethys, Telesto, Calypso, Dione, Helene, Rhea, Titan, Hyperion, Iapetus, and Phoebe.

Titan is Saturn's largest moon. It is larger than any of Jupiter's moons except Ganymede. Rhea and Iapetus are each about 1,500 kilometers (930 miles) across. Tethys and Dione are about 1,000 kilometers (620 miles) across. Mimas and Enceladus are only about 500 kilometers (310 miles) across. The rest of the moons are much smaller, and a few may be captured asteroids.

Properties

Distance from the sun	1,347 to 1,507 million kilometers

837.0 to 936.4 million miles

9.004 to 10.07 astronomical units

Sidereal period	29.457 years

10,759.22 days

Synodic period	378.09 days

Rotation period	0.44 days

Eccentricity of orbit	0.05415

Inclination of orbit	2.484 degrees

Inclination of axis	26.73 degrees

Average velocity	9.64 kilometers per second

5.99 miles per second

Mass	95.162 times that of the earth

Volume	763.59 times that of the earth

Diameter	120,536 kilometers

74,898 miles

9.449 times that of the earth

Average density	0.70 grams per cubic centimeter

Surface gravity	1.07 times that of the earth

Albedo	0.75

Atmospheric temperature	95 K

-178 C

-288 F

Escape velocity	36 kilometers per second

22 miles per second


Uranus

Overview | Interior | Surface | Atmosphere | Rings | Moons | Properties

Overview

Uranus is the seventh planet from the sun, and the first one to be discovered in modern times using a telescope. It is named after the god that personified the heavens in early Greek mythology.

William Herschel (1738-1822) discovered Uranus in 1781. On the night of March 13 he spotted an object in the constellation Gemini that he believed to be a comet. The object's movement over the following weeks allowed its orbit to be calculated, and it was soon apparent that the body was moving too slowly to be a comet. Within two months of his discovery astronomers across Europe had concluded that Herschel had discovered a new planet.

Uranus is a giant planet, but not nearly as large as Jupiter or Saturn. Uranus resembles Neptune more closely than any other planet, and these planets have therefore sometimes been referred to as twins just as Venus and the earth sometimes are.

Interior

Uranus apparently has core of rock about the size of the earth. This core may be surrounded by a layer of compressed ice, which in turn is surrounded by an ocean of water and ammonia about 6,000 kilometers (3,700 miles) deep. Although the pressure deep inside Uranus is much higher than it is inside the earth, the planet is not massive enough to create the conditions necessary for hydrogen to assume a metallic state the way it does inside Jupiter and Saturn.

Uranus has a magnetic field roughly twice as strong as the earth's magnetic field. It is tilted 60 degrees with respect to the planet's axis of rotation and is not centered on its core. Apparently the ice surrounding the core is electrically conducting, permitting it to generate the magnetic field. The reason why this material is electrically conducting and why the magnetic field has such a high inclination with respect to the rotation axis is not yet understood.

Unlike Jupiter, Saturn, and Neptune, Uranus does not radiate more energy than it receives from the sun.

Surface

Uranus doesn't have a surface in the sense that the terrestrial planets do.

Atmosphere

The Uranian atmosphere consists of about 83 percent hydrogen, 15 percent helium, and 2 percent methane. Other gases are present in very small proportions. Uranus has a much greater proportion of methane in its atmosphere than do Jupiter and Saturn. It is the methane gas that gives the planet its characteristic blue-green color.

In general, Uranus has a very clear atmosphere free of clouds. Therefore, when we look at Uranus we are seeing much further into the atmosphere than is the case for Jupiter and Saturn.

Rings

For over 300 years following the discovery of Saturn's rings, that planet was thought to be the only planet to possess such a ring system. That is, until the rings of Uranus were discovered on March 10, 1977. That night, astronomers observed Uranus using a telescope carried in a jet aircraft called the Kuiper Airborne Observatory. They were interested in measuring the light of a star as Uranus passed in front of it, hoping to learn something about the planet's atmosphere. When they noticed that the star's light flickered before and after Uranus had passed in front of it, they concluded that Uranus has rings and that these rings were blocking the star's light.

Uranus has twelve rings made of very dark, carbonaceous material. Whereas the rings of Saturn are bright and broad, and are separated by narrow gaps, the rings of Uranus are dark and narrow, and are separated by broad gaps. In fact, most of these rings are no more than about 10 kilometers (6 miles) wide. They lie between 16,300 kilometers (10,100 miles) and 25,600 kilometers (15,900 miles) above the planet's atmosphere. The ring system's thickness is very much like that of Saturn's ring system, but the particles that make up the ring system are generally much larger, at least a few centimeters (about one inch) across.

Moons

Uranus has 20 moons, 17 of which have been named: Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, Puck, Miranda, Ariel, Umbriel, Titania, Oberon, Caliban, and Sycorax. All of these moons are named for characters in plays written by William Shakespeare, and are the only bodies in the solar system not named after figures in Greek and Roman mythology.

William Herschel discovered Titania and Oberon in 1787. William Lassell discovered Ariel and Umbriel in 1851. Gerald Kuiper discovered Miranda in 1948. The Voyager 2 spacecraft discovered ten more moons when it visited the planet in 1986. The remaining five moons were discovered in 1997 and 1999 by Gladman, Karkoschka, and Kavelaars.

Properties

Distance from the sun	2,735 to 3,004 million kilometers

1,699 to 1,867 million miles

18.28 to 20.08 astronomical units

Sidereal period	84.011 years

30,685.4 days

Synodic period	369.66 days

Rotation period	0.65 days

Eccentricity of orbit	0.04718

Inclination of orbit	0.77 degrees

Inclination of axis	97.86 degrees

Average velocity	6.81 kilometers per second

4.23 miles per second

Mass	14.536 times that of the earth

Volume	63.08 times that of the earth

Diameter	51,118 kilometers

31,763 miles

4.007 times that of the earth

Average density	1.30 grams per cubic centimeter

Surface gravity	0.90 times that of the earth

Albedo	0.9

Atmospheric temperature	58 K

-215 C

-355 F

Escape velocity	21 kilometers per second

13 miles per second


Neptune

Overview | Interior | Surface | Atmosphere | Rings | Moons | Properties

Overview

Neptune is the eighth planet from the sun, and the outermost of the gas giants. It is named after the god of the sea in Roman mythology, known as Poseidon in Greek mythology.

After Uranus was discovered by William Herschel (1738-1822) in 1781, astronomers noticed that the planet's orbit did not match the one calculated it would follow, and they speculated that a yet undiscovered planet might be affecting its orbit. Two mathematicians, John Couch Adams (1819-1892) in England and Urbain Jean Joseph Leverrier (1811-1877) in France, calculated the position of this hypothetical planet.

Adams worked on the problem from 1841 to 1845 but was ignored when he presented his calculations to George Airy (1801-1892) at Greenwich Observatory. Eventually Airy asked an astronomer to look for the planet but he failed to recognize it due in part to the lack of proper star maps of the area to be searched.

Leverrier published his calculations in the summer of 1846 and eventually sent them to Johann Gottfried Galle at the Berlin Observatory who began searching for the planet on September 23, 1846. That very night an unidentified disk was observed within one degrees of where it was predicted to be. The following night the disk was observed to have moved with respect to the stars, and it was certain that a new planet had been discovered.

It was later determined that Neptune had been observed and recorded numerous times before, but that the planet had always been mistaken for a star. Galileo even saw Neptune through his crude telescope in 1610! He recorded it as a star in a sketch he made of the positions of Jupiter's moons.

Neptune resembles Uranus more closely than any other planet, and these planets have therefore sometimes been referred to as twins just as Venus and the earth sometimes are. Neptune is slightly smaller than Uranus, but is denser, meaning it is more massive than Uranus.

Interior

Neptune's core consists of rock and metal, and is surrounded by a sphere of liquid hydrogen and helium. Although the pressure deep inside Neptune is much higher than it is inside the earth, the planet is not massive enough to create the conditions necessary for hydrogen to assume a metallic state the way it does inside Jupiter and Saturn.

Neptune has a magnetic field that is about half as strong as that of Uranus, or about 500 times stronger than the earth's. It is tilted 47 degrees with respect to the planet's axis of rotation and is not centered on its core. Apparently the ice surrounding the core is electrically conducting, permitting it to generate the magnetic field. The reason why this material is electrically conducting and why the magnetic field has such a high inclination with respect to the rotation axis is not yet understood.

Like Jupiter and Saturn, Neptune radiates more energy than it receives from the sun. Neptune is apparently still radiating heat left over from its contraction into a planet billions of years ago.

Surface

Neptune doesn't have a surface in the sense that the terrestrial planets do.

Atmosphere

The atmosphere of Neptune consists of about 85 percent hydrogen, 13 percent helium, and 2 percent methane. Like Uranus, Neptune has a much greater proportion of methane in its atmosphere than do Jupiter and Saturn. It is the methane gas that gives the planet its characteristic blue-green color.

Like Uranus, Neptune's atmosphere is generally very clear and free of clouds. Therefore, when we look at Neptune we are seeing much further into the atmosphere than is the case for Jupiter and Saturn. Bright white clouds, possibly made of frozen methane ice crystals, have been observed high in the planet's atmosphere.

Neptune's atmosphere exhibits a feature known as the Great Dark Spot, a storm about the size of the earth. This storm spins counterclockwise and moves westward at about 1,200 kilometers (750 miles) per hour.

Rings

Neptune was discovered to have a ring system consisting of three narrow rings at a distance of 17,200 to 38,200 kilometers (10,700 to 23,700 miles) from its atmosphere.

Moons

Neptune has eight moons, named Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, Triton, and Nereid.

Triton, Neptune's largest moon, was discovered by William Lassell in 1846 shortly after Neptune was discovered. Nereid was discovered by Gerald Kuiper in 1949. The Voyager 2 spacecraft discovered the six remaining moons in 1989.

Properties

Distance from the sun	4,456 to 4,537 million kilometers

2,769 to 2,819 million miles

29.79 to 30.33 astronomical units

Sidereal period	164.79 years

60,189 days

Synodic period	367.49 days

Rotation period	0.77 days

Eccentricity of orbit	0.00859

Inclination of orbit	1.769 degrees

Inclination of axis	29.56 degrees

Average velocity	5.43 kilometers per second

3.37 miles per second

Mass	17.147 times that of the earth

Volume	57.74 times that of the earth

Diameter	49,528 kilometers

30,775 miles

3.883 times that of the earth

Average density	1.76 grams per cubic centimeter

Surface gravity	1.14 times that of the earth

Albedo	0.82

Atmospheric temperature	56 K

-217 C

-359 F

Escape velocity	23 kilometers per second

14 miles per second


Pluto

Overview | Interior | Surface | Atmosphere | Rings | Moons | Properties

Overview

Pluto is the planet farthest the sun. It is named after the god of the underworld in Roman mythology, known as Hades in Greek mythology.

When, in 1846, it was apparent that the orbit of Neptune did not quite match that which had been calculated, it was surmised that a yet undiscovered "Planet X" lying beyond the orbit of Neptune might be responsible. Percival Lowell (1855-1916) calculated the position of this hypothetical planet and attempted to find it from his observatory in Arizona, but was unsuccessful. An attempt to find Planet X was made in 1919 at Mount Wilson in California, but that attempt was also unsuccessful. A new wide field telescope was built at Lowell Observatory in 1929, and VM Slipher (1875-1969) decided to hire the late Clyde Tombaugh to use it to hunt for the elusive planet. Tombaugh discovered Pluto on February 18, 1930 on photographs taken with the new telescope several weeks earlier.

Pluto is not massive enough to cause the differences between Neptune's calculated and observed orbits, and this has led to speculation that yet another planet waits to be discovered. Studies of the problem conducted recently show that the differences in the orbits were perceived differences only and do not in fact exist.

Pluto's orbit has the highest eccentricity of any planet in the solar system. Pluto's orbit actually crosses the orbit of Neptune, meaning that for part of Pluto's year it is closer to the sun than Neptune is! It has in fact been closer to the sun than Neptune since 1979 and will remain so until 1999. Because Pluto's orbit is inclined by more than 17 degrees to the ecliptic, and Neptune's orbit is inclined by less than 2 degrees, there is no chance that these bodies could ever collide.

Pluto is currently the only planet never to have been visited by a spacecraft. Our knowledge of Pluto is therefore very limited. Even in photographs taken with our most powerful telescopes, Pluto reveals nothing more than a small disk of light.

Interior

Unlike the gas giants that are found closer to the sun, Pluto is a small world, only about two-thirds as large as the moon. In fact, it has been suggested that Pluto is not a "real" planet at all, but simply one of the moons of Neptune that somehow escaped its orbit. Such an event is thought to be unlikely because the planet is now known to have a moon of its own. Pluto might very well be an example of one of the types of objects that collided with each other billions of years ago to form the cores of the gas giants.

Pluto is probably composed of rock and ice. Until a space probe visits this distant world we can do little more than make educated guesses about Pluto's composition.

Surface

Although Pluto's interior may be composed of rock, its albedo is too high for a surface composed of this poor reflector of sunlight. It appears that Pluto's surface is covered with ice, which is a much better reflector of sunlight. Analysis of light reflected from Pluto's surface suggests that the ice is made of frozen methane, nitrogen, and carbon monoxide. Its surface temperature is a chilly -233 Celsius (-387 Fahrenheit).

Atmosphere

Pluto is far too cold to have an appreciable atmosphere. It appears that a very thin, temporary atmosphere of methane, nitrogen, and carbon dioxide is formed when the planet nears the sun, but that this atmosphere's gases freeze back onto the surface when the planet moves farther away.

Rings

Pluto does not have any rings.

Moons

Pluto has one moon, named Charon. This moon, discovered by James Christy and Robert Harrington in 1978, is the largest moon in proportion to the size of its planet in the solar system. Charon appears to be almost half as large as Pluto. Its surface appears to be covered in water ice rather than in methane ice.

Properties

Distance from the sun	4,425 to 7,375 million kilometers

2,750 to 4,583 million miles

29.34 to 49.30 astronomical units

Sidereal period	247.68 years

90,465 days

Synodic period	366.73 days

Rotation period	6.39 days

Eccentricity of orbit	0.2488

Inclination of orbit	17.14 degrees

Inclination of axis	122.46 degrees

Average velocity	4.74 kilometers per second

2.95 miles per second

Mass	0.0021 times that of the earth

Volume	0.0057 times that of the earth

Diameter	2,302 kilometers

1,430 miles

0.180 times that of the earth

Average density	2.10 grams per cubic centimeter

Surface gravity	0.06 times that of the earth

Albedo	0.145

Surface temperature	40 K

-233 C

-387 F

Escape velocity	1 kilometer per second

0.6 miles per second


No Help available

No Help is available for this area of the application's window.


Window border

The window border is located along each edge of the application's window.

Click the window border with the left mouse button and then drag the mouse to change the size of the window.


Title bar

The title bar is located along the top of the application's window. It contains the application's Control menu, name, and minimize, maximize, restore, and close buttons.

Click the title bar with the left mouse button and then drag the mouse to change the position of the window. Double-click the title bar with the left mouse button to maximize or restore the window.

Minimize button

Click this button to collapse the window to an icon.

Maximize button

Click this button to expand the window to fill the available space.

Restore button

Click this button to restore the window to the position and size it had before you maximized it.

Close button

Click this button to close the window and exit the application.


Restore command (Control menu)

Use this command to restore the application's window to the position and size it had before you used the Minimize or Maximize command.


Move command (Control menu)

Use this command to change the position of the application's window using the arrow keys. When you use this command, the pointer will turn into a four-headed arrow. Press the arrow keys to move the window, and then press the Enter key.


Size command (Control menu)

Use this command to change the size of the application's window using the arrow keys. When you use this command, the pointer will turn into a four-headed arrow. Press an arrow key to move the pointer to the window border you want to move. The pointer will then turn into a two-headed arrow. Press the arrow keys to make the window larger or smaller, and then press the Enter key.


Minimize command (Control menu)

Use this command to collapse the application's window to an icon. Use the Restore command to restore the window to the position and size it had before you used the Minimize command.

Minimize button

Click this button to execute this command.


Maximize command (Control menu)

Use this command to expand the application's window to fill the available space. Use the Restore command to restore the window to the position and size it had before you used the Maximize command.

Maximize button

Click this button to execute this command.


Close command (Control menu)

Use this command to close the application's window and exit the application.

Close button

Click this button to execute this command.

Shortcut

Press the Alt+F4 keys.


Help command

Use this command to switch the application into context-sensitive Help mode. When you use this command, the pointer will turn into an arrow and question mark. While the program is in context-sensitive Help mode, click on a menu command, toolbar button, or any area of the window to display the Help topic associated with the command, button, or area.

Help button

Click this button to execute this command.

Shortcut

Press the Shift+F1 keys.


Status bar

The status bar is displayed across the bottom of the application's window, below the sky chart. It contains a description of the action performed by the menu command currently selected, or by the toolbar button currently under the pointer. The two panes in the right part of the status bar display the name and coordinates of the location from which you are viewing the sky.

Use the Status Bar command on the View menu to display or hide the status bar.

The status bar also displays the angular separation between two points in the display. To measure an angular separation, move the pointer over the first point, click and hold down the left mouse button, drag the pointer to the second point, and then release the button.

The angular separation between the two points will be displayed in the status bar until another message takes its place.


Center command

Centers a point when you right-click on it and choose this command from the popup menu that appears.


About Star command

Displays data about a star when you right-click on it and choose this command from the popup menu that appears.


About Deep Sky Object command

Displays data about a deep sky object when you right-click on it and choose this command from the popup menu that appears.


About Planet command

Displays data about a planet when you right-click on it and choose this command from the popup menu that appears.


About Sun command

Displays data about the sun when you right-click on it and choose this command from the popup menu that appears.


About Moon command

Displays data about the moon when you right-click on it and choose this command from the popup menu that appears.


No Help available

No Help is available for this message box.


View toolbar

The View toolbar is initially displayed across the top of the sky chart, below the menu bar and to the left of the Animation toolbar. It contains buttons that deal with printing a sky chart, previewing a printed sky chart, changing the zoom level, displaying a standard horizon or zenith view, scrolling the sky chart, and obtaining context-sensitive Help.

Use the View Toolbar command on the View menu to display or hide the View toolbar.

To turn a docked toolbar into a floating toolbar, move the pointer over the empty area around the toolbar's buttons, press and hold down the mouse button, and then drag the pointer away, toward the center of the sky chart. When the toolbar's outline has changed shape and is where you want it, release the mouse button.

To turn a floating toolbar into a docked toolbar, move the pointer over the toolbar's title bar, press and hold down the mouse button, and then drag the pointer to any edge of the sky chart. When the toolbar's outline has changed shape and is where you want it, release the mouse button.

When you move the pointer over a toolbar button and wait a second you'll see the name of the button appear in a small ToolTip window. A short description of the button will also appear in the left part of the status bar.


Left command (View toolbar)

Scrolls the sky chart to the left.

Left button

Click this button on the View toolbar to execute this command.

Shortcuts

Press the Left Arrow key. Press the Ctrl+Left Arrow keys to scroll the sky chart in smaller steps.


Up command (View toolbar)

Scrolls the sky chart up.

Up button

Click this button on the View toolbar to execute this command.

Shortcuts

Press the Up Arrow key. Press the Ctrl+Up Arrow keys to scroll the sky chart in smaller steps.


Down command (View toolbar)

Scrolls the sky chart down.

Down button

Click this button on the View toolbar to execute this command.

Shortcuts

Press the Down Arrow key. Press the Ctrl+Down Arrow keys to scroll the sky chart in smaller steps.


Right command (View toolbar)

Scrolls the sky chart to the right.

Right button

Click this button on the View toolbar to execute this command.

Shortcuts

Press the Right Arrow key. Press the Ctrl+Right Arrow keys to scroll the sky chart in smaller steps.