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ASTRO Version 2.02 Athabasca University Micro-Planetarium User Documentation Revision 1.11 Malcolm Reeves 8 July 1992 Documentation Conventions < > are used to indicate keystrokes. For example, <Alt_X> means hold down the <Alt> key and press <X>. Multiple keystrokes are separated by commas, for example <Alt_P>, <Shift P>. [ ] are used to indicate menu selections. For example, [Plot] means the [Plot] selection from a menu. Multiple menu levels are indicated by adjacent selections, for example [Options] [General] means the [General] selection from the [Options] menu. { } are used to indicate button icons. For example, {Planets} means the planets icon in the graphical user interface. GIF(tm) and Graphical Interchange Format (tm) are trademarks CompuServe Inc, an H&R Block Company. MS-DOS(tm) is a trademark of the Microsoft Corporation. Acknowledgements ASTRO algorithms are drawn from "Astronomical Formulae for Calculators" by J.Meeus, 3rd Ed., 1985, Willman-Bell Inc, 214pp and "Astronomy with your personal computer" by P.Duffett Smith, 1985, Cambridge University Press, 256pp. Some windows code is based on "User Interfaces in C++" by Mark Goodwin, 1989, MIS:Press, 394pp. Some graphics code is based on "Graphics programming in C" by Roger Stevens, 1988, M&T Books, 639pp The GIF(tm) code is based on recoded functions from GifLib Version 1.2 by Gershon Elber. The original version of ASTRO was written by Tony Willis. The author is grateful to Martin Connors and Garth Edwards for their reviews and encouragement. ASTRO 2.02 (C) Malcolm Reeves, 1992. All Rights Reserved. ASTRO: TABLE OF CONTENTS ASTRO: GETTING STARTED 1.0 Introduction 4 1.1 Hardware Requirements 4 1.2 User Interfaces 4 1.3 Getting Started 4 1.4 Saving Your Work 9 1.4.1 Printer Screen Dumps 9 1.4.2 Graphics Interchange Format Files (GIF) 10 ASTRO: TEXT-MENU SYSTEM 2.0 Introduction 11 2.1 Info <Alt_I> 11 2.1.1 Help 11 2.1.2 Defaults 12 2.1.3 About 13 2.2 Data <Alt_D> 13 2.2.1 Position 13 2.2.2 Date and Time 13 2.2.3 Star Catalog 14 2.3 Options <Alt_O> 14 2.3.1 General 14 2.3.2 Animation 15 2.3.3 Star Magnitude 15 2.3.4 Star Color 15 2.3.5 Solar System 16 2.3.6 Output 17 2.4 Plot <Alt_P> 17 2.4.1 Plot Star Map 17 2.4.2 Cancel 18 2.5 Exit <Alt_X> 18 2.5.1 Exit to DOS 18 2.5.2 Cancel 18 ASTRO: GRAPHICAL USER INTERFACE BUTTONS 3.0 Introduction 19 3.1 Toggles 19 3.1.1 Sun and Moon <Alt_S> 19 3.1.2 Planets <Alt_P> 19 3.1.3 Star Magnitude <Alt_M> 19 3.1.4 Star Color <Alt_C> 19 3.1.5 Animation <Alt_A> 20 3.1.6 Grids <Alt_G> 20 3.1.7 Lines and Planes <Alt_L> 20 3.1.8 Text <Alt_T> 20 3.1.9 Daylight Savings <Alt_D> 20 3.2 Time-Stepping and Animation 21 3.2.1 Solar Time Step <Hh> or <Dd> or <Mm> or <Yy> 21 3.2.2 Sidereal Time Step <Ss> or <Ll> 21 3.2.3 Animation Toggle <Alt_A> 21 3.2.4 Stop and Redraw <Esc> 22 3.3 Pan and Zoom 22 3.3.1 Pan Up <Up_Arrow> 22 3.3.2 Pan Down <Down_Arrow> 22 3.3.3 Pan Left <Left_Arrow> 22 3.3.4 Pan Right <Right_Arrow> 22 3.3.5 Zoom Up <+> 22 3.3.6 Zoom Down <-> 22 3.3.7 Restore Pan-Zoom <Alt_H> or <Home> 22 3.4 Save Screen Output <Alt_O> 22 3.5 Exit to Text-Menus <Alt_Q> or <Alt_X> 23 ASTRO: APPLICATIONS AND EXERCISES 4.0 Introduction 24 4.1 Motions of the Sun and Moon 24 4.1.1 Orbital Period of the Moon 24 4.1.2 Changes in Altitude of the Sun 26 4.2 Planetary Motions 26 4.2.1 Apparent Star Motions 26 4.2.2 Retrograde Planetary Motion 27 4.2.3 Orbital Period of the Planets 27 4.3 Proper Motions of the Stars 28 4.4 Distances to the Stars 29 4.5 Distribution of Stars in the Galaxy 30 ASTRO: DEVELOPMENT HISTORY 5.0 Introduction 32 5.1 Star Catalog File Format 32 5.2 Version 1.0 32 5.3 Version 2.0 32 5.4 Future Developments 33 5.5 Version 2.xx Revisions and Changes 33 ASTRO : GETTING STARTED 1.0 Introduction ASTRO is the Athabasca University Micro-Planetarium Program written to support the Science 280 course "Introduction to Astronomy and Astrophysics". 1.1 Hardware Requirements ASTRO will run on 8088, 8086 and 80x86 machines under MS- DOS Version 2.1 or higher. It requires approximately 150K of RAM to execute. The program will use (but does not require) an MS-compatible mouse and 8087/80x87 math-coprocessor. ASTRO autodetects the video hardware and supports CGA, EGA, VGA and ATT graphics in 2 and/or 16 color modes. Hercules graphics are not currently supported. Hercules users may be able to use CGA/EGA emulators for ASTRO but the ability to save and print screens may not be supported. 1.2 User Interfaces ASTRO has both text-menu and graphical user interfaces. At startup, the text-menu interface appears with a title bar, pulldown menu bar and status line. The pulldown selections are [Info], [Data], [Options], [Plot], [Exit]. The menus are activated either by mouse, arrow-keys, or Alt- keys (for example <Alt_X> for [Exit]). The Alt-key for a particular item is highlighted. The status line at the bottom of the screen indicates the video display adapter that has been autodetected. The graphical user interface (GUI), is accessed by selecting [Plot Star Map] from the [Plot] pulldown menu. It comprises a set of icon-buttons that control the sky display panel. 1.3 Getting Started To start the program, make the directory in which ASTRO is stored the current directory and enter "astro" at the DOS prompt: C:\ASTRO> astro A:\> astro For EGA/VGA systems without 16-color capability, add the command-line switch "-bw" to force 2-color video display: C:\ASTRO> astro -bw The command-line switches "-cga" and "-ega" may be used to override the autodetection of ASTRO. Note: in such cases ASTRO assumes the hardware is capable of the requested video mode. At startup, the text-menu interface should appear with a title bar, pulldown menu bar, and status line. ASTRO provides default data so no data entry is required. MOUSE: Click on the [Plot] pulldown menu and select the first item [Plot_Star_Map]. KEYS: Press <Alt_P>,<Return> or <Alt_P>,. The graphical user-interface (GUI) should now replace the text-menu display on the screen. The GUI is divided into two panels, on the left the button and information panel, and on the right, the sky display (See page 4). At the top of the button-panel, below the title line, are three legends used to indicate star magnitude (from -1 to +4), star color index (O to M), and 10 solar-system objects (Sun, Mercury, Venus, Moon, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto). The Sun and Moon are represented as squares and the planets as diamonds. For black and white displays, (CGA, ATT6300, or EGA/VGA 2-color modes) the color-index legend will NOT appear. Below the legends, an information panel gives the observer location and observation time. If a mouse was detected, an additional information line appears for azimuth and altitude (the current pointer position on the sky panel). MOUSE: Move the mouse onto the sky panel and check that the cross in the centre of the circle (the zenith point) labelled "Z", returns the altitude coordinate 90 and that points on the circumference return 0. The azimuth values should increase from 0-360 anticlockwise from the top of the circle. KEYS: Press <Alt_G> to turn on the altitude-azimuth grid. The radial lines (azimuth) and concentric circles (altitude) are 15 degrees apart and can be used to estimate coordinates. Press <Alt_G> again to toggle the grid off. The GUI button-panel has 25 function buttons. The functions are explained in detail later in this manual and in the on-line help files (accessed from the text-menu interface). For a new-user, there are two important buttons to remember: MOUSE: The exit button, {Big Q} icon and the animation toggle, {Big A} icon. Click on {Big A} and the display on the right will step forwards or backwards in time (the default step is one sidereal day.) During animation the mouse pointer is disabled so to stop the animation you must hit <Esc> or <Alt_A>. KEYS: <Alt_Q> or <Alt_X> will Exit the GUI to the text-menu interface. <Alt_A> is a toggle to start and stop animation. <Esc> will also halt time-step animation. There is an important different between using <Alt_A> and <Esc> to halt an animation sequence. <Alt_A> preserves the display with the "trails" of the animated objects. Hit <Alt_A> again and the animation continues as if nothing had happened. <Esc> erases all trails and redraws the sky for the stop-time. The sky panel, on the right hand side of the screen, is the main display area. In the default startup configuration, you see a big circle (the horizon), a cross at the centre (the zenith point) and a square (the Moon). If you tried out animation, there may be some dots representing the track of the moon (and possibly the sun). If the time and date is not 21:00:00 10/02/1989, reset it using the time-step buttons in the lower left hand corner of the display. The highlighted ("turned on") arrowhead indicates the current direction of time (Up forwards, Down backwards). The {Double Letter} or {*} icons indicate the current solar ({HH} or {DD} or {MM} or {YY}) or sidereal ({*} or {Three_*}) time-step. MOUSE: Click on {Up_Arrow} to increment or {Down_Arrow} to decrement time by one step. To cycle the solar step from hours to days to months to years and back to hours click on {Double Letter}. Click on the {*} to change the sidereal interval to the long {Three_*} step of 100,000 sidereal days (273 years). The icon changes to 3 asterisks arranged in a triangle. KEYS: <H> <D> <M> <Y> increment, <h> <d> <m> <y> decrement the solar time-step. <S> <L> increment <s><l> decrement the sidereal time-step. ( S-for-short, one day; L-for-Long, 100,000 days). Note: the display is redrawn for every mouse-click or keystroke. On a slow machine, it may be better to exit the GUI and reset the time and date in the pulldown [Data] menu. Assuming, we are back in the GUI at 21:00:00 10/02/1989, we can add more to the display: MOUSE: Click on {Planet} icon (the blob with the thick line through it) and, for the default configuration, two planets (Mars and Jupiter) appear below and slightly to the left of the Moon. The display should resemble the picture on page 4. Mars is nearest the Moon. Click {Planet} again and the planets disappear. KEYS: <Alt_P> P-for-Planets toggles the display of planets. Wait for the screen to redraw between keystrokes, on slow machines this may take a few seconds. Try not to accumulate too many keystrokes as ASTRO will save and process them all e_v_e_n_t_u_a_l_l_y! ASTRO toggles, in addition too the {Planets} toggle, include: Sun and Moon <Alt_S> S-for-Sun Star Magnitude <Alt_M> M-for-Magnitude Star Color <Alt_C> C-for-Color index Altitude-Azimuth Grid <Alt_G> G-for-Grid Ecliptic and Celestial Equators and Galactic Plane <Alt_L> L-for-Lines Deciphering the icons is left as an exercise (if intuition fails the Alt-keys still work, even if you have a mouse). If tried <Alt_M> or <Alt_C> you are now asking: WHY ARE THERE NO STARS? The software features a cloudy night mode perhaps.....? The real reason is, that the default action of ASTRO is not to read the star catalog stored in the support file "YALE.BIN". This file is not needed for solar system objects and must be read explicitly from the [Data] menu. To read the file, return to the text-menu interface <Alt_Q> or click on {Big Q} and select [Star_Catalog] from the [Data] pulldown menu, the keystrokes are <Alt_D>,<S> D-for-Data, S-for-Star. Now return to the GUI, from the [Plot] pulldown menu select [Plot_Star_Map] with the mouse or <Alt_P>,. Make sure that the date and time are the defaults 21:00:00 10/02/1989 and toggle the star magnitude display <Alt_M>. You should be able to see the Big Dipper to the left and slightly above the zenith point. Check out the pointer to Polaris directly above the zenith. The very large point a little above the southern horizon is Sirius. It has a special symbol with a cross through the "circle" to make it easy to find. Look slightly above (to the North) of Sirius and right (to the West) to find Orion. The three belt stars merge on the current display scale. COLOR MONITOR: Flip to star color display <Alt_C>. Sirius is green, Betelgeuse (top left in Orion) is red, Rigel (bottom right in Orion) is cyan. BW MONITOR: Take a break, or check out the [Star_Color] selection in the text-menu interface. This allows selective display of stars by spectral class. The lower right region of the button-panel is used to pan and zoom the sky map. To resolve the belt stars in Orion, for example. Click on {Down_Arrow} or press the <Down_Arrow> key to pan down. The sky map appears to move up. Now click on {+} or press the <+> key and the screen is redrawn at a larger scale. If you have a slow cpu, and you are displaying 526 stars, the redraw may take about a minute. In such cases, you may prefer to turn off the stars <Alt_M> and planets <Alt_P>, pan and zoom to where you want to be, then toggle the stars and planets on again. Try panning and zooming around the sky. ASTRO has a maximum zoom factor of x16 that increases or decreases by one for every mouse click or keystroke. To restore the original display, at any time, click on the big "H" or press <Home> or <Alt_H> H-for-Home. If you exit the GUI for any reason, when you return ASTRO remembers the toggle and pan-zoom state and restores the display. On final feature of note in ASTRO is the on-line help. Return to the text-menu interface {Big Q} or <Alt_Q> or <Alt_X>. Press <Alt_I> to activate the [Info] menu. Now select [About] or press <A> A-for-About, to see who is responsible for ASTRO and this documentation. Any key stroke or mouse-click will dismiss this blatant piece of self-aggrandizement. Next select [Help]. Guess which key? From the options in the [Help] menu, select [Menus], a help window will pop- up on the left-hand side of the screen. Press any key or click on the arrow on the title bar to close the help window. Now select [GUI Buttons], this is a more extensive piece of text so the window has a scroll bar. Use the mouse on the arrowheads on the scroll bar or the arrow keys to scroll. Outside the [Info] [Help] menu, hitting <F1> will bring up an appropriate help message EXCEPT from the pulldown menu bar. This has been a very brief basic introduction to ASTRO. For a comprehensive reference, see section 2 for text-menus and section 3 for the GUI buttons. For some guidance on the applications for ASTRO see section 4. Section 5 features a brief description of the development history of ASTRO. 1.4 Saving Your Work Hardcopy from ASTRO can be obtained by selecting the printer icon from the GUI or press <Alt_O> O-for-Output. This causes the program to write the complete screen to a file in one of four in standard formats: 1. PRN file - IBM/Epson compatible screen dump. 2. PCL file - HPCL (Hewlett-Packard Print Control Language) screen dump. 3. EPS file - Encapsulated Postscript screen dump. 4. GIF file - GIF87a screen image. ASTRO does NOT support direct printing. An intermediate file MUST be generated. Users are recommended to use GIF files. 1.4.1 Printer Screen Dumps PRN files are 37-45K depending on the screen mode. They can be copied to any Epson- compatible printer. PCL files are similar screen dumps for HPCL-compatible printers (such as the Laserjet). File sizes are similar to those for the Epson printer. EPS files are VERY LARGE. About 600K+ for a vga color screen. Take care that disk- space is available when attempting to save the screen in this form. EPS files can be copied to any Postscript printer. It is NOT necessary to use the MS-DOS utility "GRAPHICS.COM" to print files generated by ASTRO. When using the MS-DOS copy command, the /b (binary) switch on the command-line MUST be used for .PRN and .PCL binaries or the screen dump may be incomplete. C:\ASTRO> copy astroXXX.prn lpt1: /b Epson compatible C:\ASTRO> copy astroXXX.pcl lpt1: /b Hewlett-Packard compatible C:\ASTRO> copy astroXXX.eps lpt1: Postscript compatible If files are to be saved or transferred to other systems (eg Unix, VMS), then it is recommended that Postscript files be compressed with ZOO, ZIP or ARC compressors. This can reduce a 630K file (640x480 VGA screen) to about 13K. REMEMBER: PRN, PCL, ZIP, ZOO and ARC files are binary formats (set the transfer type to binary). EPS files are in ascii. 1.4.2 Graphics Interchange Format Files GIF files are the recommended form of output from ASTRO. They provide a valuable compact pictorial record in machine-readable form and can be readily printed. A typical GIF is only 5-8K for the full-screen. GIF file can be viewed or printed with a suitable utility. There are many excellent freeware and shareware GIF utilities for viewing, manipulating and printing GIF files. These include CSHOW, VPIC, VUIMG and GIFPRT. C:\ASTRO> gif2scr astroXXX.gif Try your local BBS or the DOS directories on the AU computer system to obtain a copy of the latest version of such a package. Remember to register the one you choose to use - you can try them out FREE! ASTRO : TEXT-MENU SYSTEM 2.0 Introduction The text-menu interface comprises a desktop with a title bar, pulldown menu bar and status line. The pulldown selections are [Info], [Data], [Options], [Plot], and [Exit]. The menus are activated either by mouse, arrow-keys, or Alt-keys (for example <Alt-X> for [Exit]. The Alt-key for a particular item is highlighted. ┌───────────────────────────────────────────────────────────────┐ │ Info Data Options Plot Exit │ └───────────────────────────────────────────────────────────────┘ The status line at the bottom of the screen indicates the video display adapter that has been autodetected (even if a command-line switch was used to override). 2.1 Info <Alt_I> The [Info] pulldown menu (keystroke <Alt_I>) has three selections [Help], [Defaults], [About]. ┌───────────────────────────────────────────────────────────────┐ │ Info Data Options Plot Exit │ ├──────────┬────────────────────────────────────────────────────┘ │ Help │ │ Defaults │ │ About │ └──────────┘ The [Help] selection pops up a list of help categories, [Defaults] allow inspection of current parameter settings and [About] gives some information about the version and author of ASTRO. 2.1.1 Help The [Help] selection (keystroke <H>) pops up a window of help categories: ┌───────────────┐ │ Help │ Keystroke ├───────────────┤ │ Data Entry │ <D> │ General │ <G> │ GUI Buttons │ │ Hardware │ <H> │ Menus │ <M> │ Status Panels │ <S> └───────────────┘ To select a category, enter the highlighted keystroke, click on the option with the mouse or move to the option with the arrow keys and hit return. When a category is selected, a help window will pop-up on the left-hand side of the screen. Press any key or click on the arrow on the title bar to close the help window. The more extensive help windows have a scroll bars. Use the mouse on the arrowheads on the scroll bar or the arrow keys to scroll the text up and down. Outside the [Info] [Help] menu, hitting <F1> will bring up an appropriate help message. 2.1.2 Defaults The [Defaults] selection (keystroke <D>) pops up information panels for current parameter settings but does NOT allow editing. The settings may be edited from the [Data] and [Options] menus. ┌────────────────────┐ │ Defaults │ Keystroke ├────────────────────┤ │ Space-Time Co-ords │ <T> │ General │ <G> │ Animation │ <A> │ Star Magnitude │ <M> │ Star Color │ <C> │ Solar System │ <S> │ Output │ <O> └────────────────────┘ To select a category, enter the highlighted keystroke, click on the option with the mouse or move to the option with the arrow keys and hit return. When a category is selected, an information panel will pop-up on the right of the screen. Only one panel is displayed at a time and the [Defaults] menu bar remains on the screen. A mouse click or the <Esc> key will dismiss the panel. The [Space-Time_Co-ords] information panel gives the observers position in time and space. Latitude, longitude, azimuth, date and time parameters are shown. The defaults are the Latitude and Longitude of Athabasca, Alberta looking south (azimuth 180°) in winter on 10 February 1989 at 21:00 hrs (9:00pm). The [General] information panel comprises a series of toggles for items to be shown on sky plots. The symbol [■] next to an option indicates that it is selected. By default the options to show the Sun and Moon, the ecliptic and celestial equators, and the galactic plane are enabled. The planets and stars options are disabled. See the [Options] menu for further details. The [Animation] information panel shows the animation time-step and the number of steps per animation period. The defaults settings are for 100 steps of one sidereal day. The [Star Magnitude] information panel shows the magnitude range(s) for which stars will be displayed. The default is to make stars of every magnitude visible. The [Star Color] information panel shows the spectral classes (O-M) or (blue to red) of stars to be displayed. All spectral classes are selected by default. The [Solar System] information panel shows a list of solar system objects that can be displayed. By default, all objects, Sun, Moon and planets will be visible. The [Output] information panel indicates the form in which the sky panel plot may be saved. The default is [None] - nothing will be saved. The options consist of a set of file formats for saving the graphics screen. 2.1.3 About The [About] selection (keystroke <A>) pops up a window with information about the version and authorship of Astro. The about window is dismissed by the <Esc> key or a mouse-click outside it's borders. 2.2 Data <Alt_D> The [Data] pulldown menu (keystroke <Alt_D>) has three selections [Position], [Date and Time], [Star Catalog]. ┌───────────────────────────────────────────────────────────────┐ │ Info Data Options Plot Exit │ └─────┬───────────────┬─────────────────────────────────────────┘ │ Position │ │ Date and Time │ │ Star Catalog │ └───────────────┘ These menu selections provide for the entry of the observer position (latitude, longitude) and viewing direction (azimuth); date (dd/mm/yyyy) and time (hh:mm:ss) of observation; and reading the support file "YALE.BIN" containing the data for the 526 brightest stars. 2.2.1 Position The [Position] menu selection (keystroke ) pops up a dialog box with the current defaults for latitude, longitude and azimuth in (degs, mins, secs). Enter new values by overtyping. The cursor will automatically skip non-numeric characters thus to enter the latitude for Edmonton (53°35'00") type only 0533500 or +5335. Notice that leading zeros are required for all fields but that trailing zeros may be omitted. Latitude values must be in the range +90 to -90, positive values are North of the equator. Longitude values must be in the range 0 to 360 increasing from North in the sense NWSE (counter clockwise) so that Edmonton is 113°31'30". The same numerical longitude East of Greenwich is 290°31'30" (close to Canton, China). The NWSE direction convention is used so that North American longitudes are in the range 0-180. Azimuth values (the direction of view) must also be in the range 0 to 360 increasing from North in the sense NESW (clockwise) so that NE is 45° and NW is 315°. 2.2.2 Date and Time The [Date and Time] menu selection (keystroke <D>) pops up a dialog box with the current defaults for date (dd/mm/yyyy) and time (hh:mm:ss). Enter new values by overtyping. The cursor will automatically skip non-numeric characters thus to enter the date 1 Jan 1992 type only 01011992. Notice that leading zeros are required for the day and month fields. Times must be in the range 00:00:00 to 24:00:00. 2.2.3 Star Catalog The [Star Catalog] menu selection (keystroke <S>) causes the program to attempt to read the file "YALE.BIN" from the current DOS directory. A message box appears to indicate reading is being attempted. If the read fails a dialog box pops up and requires an acknowledging keystroke <Any> or mouse click. If the read succeeds a dialog box pops up indicating the number of star data records read in. Again an acknowledgement is required before the program continues. ASTRO does not need to read this file. The motions of the Sun, Moon and planets can be studied without these data. 2.3 Options <Alt_O> The [Options] pulldown menu (keystroke <Alt_O>) has six selections [General], [Animation], [Star Magnitude], [Star Color], [Solar System] and [Output]. [Options] provides editing access. ┌───────────────────────────────────────────────────────────────┐ │ Info Data Options Plot Exit │ └───────────┬────────────────┬──────────────────────────────────┘ │ General │ │ Animation │ │ Star Magnitude │ │ Star Color │ │ Solar System │ │ Output │ └────────────────┘ The defaults for the GUI have been carefully selected and users with slow cpus are strongly advised to use these (at least in the first instance). 2.3.1 General The [General] selection (keystroke <G>) pops up a window of general options for the sky panel. ┌─────────────────────┐ │ General │ Keystroke ├─────────────────────┤ │ ■ Sun and Moon │ <S> │ Planets │ │ Star Magnitude │ <M> │ Star Color │ <C> │ ■ Ecliptic Equator │ <E> │ ■ Celestial Equator │ <L> │ ■ Galactic Plane │ <G> └─────────────────────┘ The first 4 options can be reset from within the GUI. The final three options, to show ecliptic and celestial equators and galactic plane, can only be enabled in this menu. Options tagged by [■] are enabled. To toggle the status of an option, enter the highlighted keystroke, click on the option with the mouse or move to the option with the arrow keys and hit return. The [Sun and Moon], [Planets], [Star_Magnitude] and [Star_Color] options are enabling toggles that are duplicated as buttons in the GUI. [Star_Magnitude] and [Star_Color] are mutually exclusive. Equators and planes can be switched on and off as a group but NOT individually, by a button in the GUI. This menu enables a subset of planes to be selected for display. The option window is dismissed by the <Esc> key or a mouse-click outside it's borders. 2.3.2 Animation The animation option allows the user to select the number of time-steps to advance for an animation period. The default is 100. A higher number may be appropriate for a fast cpu. The time-step can be set from the GUI but the number of steps cannot. 2.3.3 Star Magnitude The [Star Magnitude] selection (keystroke <M>) pops up a window of magnitude range options: ┌─────────────────┐ │Magnitude Options│ Keystroke ├─────────────────┤ │ All │ <L> │ ■ < -1.0 │ <<> │ ■ -1.0 to 0.0 │ <0> │ ■ 0.0 to 1.0 │ <1> │ ■ 1.0 to 2.0 │ <2> │ ■ 2.0 to 3.0 │ <3> │ ■ 3.0 to 4.0 │ <4> │ ■ > 4.0 │ <>> │ None │ <E> └─────────────────┘ Options tagged by [■] are enabled. To toggle the status of an option, enter the highlighted keystroke, click on the option with the mouse or move to the option with the arrow keys and hit return. All options are enabled by default. This menu enables a subset of stars to be selected for display by magnitude. The option window is dismissed by the <Esc> key or a mouse-click outside it's borders. The [All] and [None] selections toggle every magnitude range on and off. Note: the use of <l> for "All" and <e> for "None" is for consistency with other menus where <A> and <N> are used for other selections. 2.3.4 Star Color The [Star Color] selection (keystroke <C>) pops up a window of spectral class options: ┌──────────────────┐ │ Color Options │ Keystroke ├──────────────────┤ │ All │ <L> │ ■ O blue │ <O> │ ■ A blue-green │ <A> │ ■ B green │ │ ■ F white │ <F> │ ■ G white-yellow │ <G> │ ■ K orange-red │ <K> │ ■ M red │ <M> │ None │ <E> └──────────────────┘ Options tagged by [■] are enabled. To toggle the status of an option, enter the highlighted keystroke, click on the option with the mouse or move to the option with the arrow keys and hit return. All options are enabled by default. This menu enables a subset of stars to be selected for display by color (really spectral class). The option window is dismissed by the <Esc> key or a mouse-click outside it's borders. The [All] and [None] selections toggle every spectral class on and off. 2.3.5 Solar System The [Solar System] selection (keystroke <S>) pops up a window of options for the display of the Sun and Moon, and planets: ┌────────────┐ │ SS Options │ Keystroke ├────────────┤ │ All │ <L> │ ■ Sun │ <S> │ ■ Moon │ <O> │ ■ Mercury │ <R> │ ■ Venus │ <V> │ ■ Mars │ <M> │ ■ Jupiter │ <J> │ ■ Saturn │ <T> │ ■ Uranus │ │ ■ Neptune │ <N> │ ■ Pluto │ │ None │ <E> └────────────┘ Options tagged by [■] are enabled. To toggle the status of an option, enter the highlighted keystroke, click on the option with the mouse or move to the option with the arrow keys and hit return. The [Sun and Moon] selection in [General] enables the group Sun and Moon, the [Planets] selection enables the remainder. This set of options allows a subset of planets to be selected for display or the Sun or Moon to be isolated. The groups selected here may be toggled on and off in the GUI. The option window is dismissed by the <Esc> key or a mouse-click outside it's borders. The [All] and [None] selections toggle every solar system object on and off. 2.3.6 Output The [Output] selection (keystroke <O>) pops up a window of screen output options: ┌────────────┐ │ Output │ Keystroke ├────────────┤ │ ■ None │ <N> │ PRN File │ │ PCL File │ <C> │ EPS File │ <E> │ GIF File │ <G> └────────────┘ Options tagged by [■] are enabled. To toggle the status of an option, enter the highlighted keystroke, click on the option with the mouse or move to the option with the arrow keys and hit return. PRN, PCL and EPS files are the equivalent of a screen dumps to IBM/Epson, Hewlett Packard and Postscript compatible graphics printers. The GIF file is in GIF87a format. The option window is dismissed by the <Esc> key or a mouse-click outside it's borders. Multiple files may be written if the appropriate options are enabled. Note: in such cases ASTRO may have to scan the screen image more than once and the operation may take a significant amount of time. A line is drawn on the right hand side or at the bottom of the screen to indicate the progress of a screen dump. The line is erased when the dump is complete. 2.4 Plot <Alt_P> The [Plot] pulldown menu has only two options: [Plot Star Map] and [Cancel]. ┌───────────────────────────────────────────────────────────────┐ │ Info Data Options Plot Exit │ └────────────────────┬───────────────┬──────────────────────────┘ │ Plot Star Map │ │ Cancel │ └───────────────┘ The [Cancel] option enables the user to avoid the time-penalty of accidentally entering the GUI. 2.4.1 Plot Star Map The [Plot Star Map] selection (keystroke ) transfers from the text-menu interface to the graphical interface of ASTRO. Before entering the GUI, the <F1> key will pop up a useful help window. 2.4.2 Cancel The [Cancel] selection (keystroke <C>) simply causes ASTRO to exit from the [Plot] pulldown menu. 2.5 Exit <Alt_X> The [Exit] pulldown menu has only two options: [Exit] and [Cancel]. ┌───────────────────────────────────────────────────────────────┐ │ Info Data Options Plot Exit │ └──────────────────────────┬─────────────┬──────────────────────┘ │ Exit to DOS │ │ Cancel │ └─────────────┘ The [Cancel] option is a safety feature to avoid loss of work by inadvertent exit. 2.5.1 Exit to DOS The [Exit] selection (keystroke <X>) returns to DOS. 2.5.2 Cancel The [Cancel] selection (keystroke <C>) simply causes ASTRO to exit from the [Exit] pulldown menu. ASTRO : GRAPHICAL USER INTERFACE BUTTONS 3.0 Introduction The graphical user interface (GUI), is accessed by selecting [Plot Star Map] from the [Plot] pulldown menu. It comprises a set of 25 icon-buttons that control the sky display panel. Many of the buttons can be preset in the text-menu interface affording flexibility. This feature is particularly valuable to users with a slow cpus since GUI redraw-overhead can be avoided by exit to the text-menu for option changes. 3.1 Toggles Toggles are switches that cycle the on/off condition. The GUI has a number of such switches. On color displays, when a switch is toggled the icon on the button changes from dark gray (on) to white (off). On black and white displays, the icon switches from black on white (on) to white on black (off). On some 2-color laptop displays this may be reversed. Check the defaults to find the sense of the display for such cases. The {Sun and Moon} toggle is on in the default startup data. 3.1.1 Sun and Moon <Alt_S> The {Sun and Moon} icon (keystroke <Alt_S>) is two overlapping circles in different colors. The button toggles the display of the Sun and Moon on the sky panel. Objects (Sun or Moon) that have been "turned off" in the [Solar System] options menu are not displayed. 3.1.2 Planets <Alt_P> The {Planets} icon (keystroke <Alt_P>) is a circle with a diagonal line through the centre. The button toggles the display of the planets on the sky panel. Only those planets that have been "turned on" in the [Solar System] options menu are displayed. Note: the contrast for red against the default star panel background (blue) is poor. The "trail" of the planet Mercury may be difficult to discern for some users. In such cases, try adjusting the contrast and brightness controls on your monitors. On 2-color displays, all trails are white-on-black. Users are advised to isolate one or two objects in the [Options][Solar_System] menu before plotting trails. 3.1.3 Star Magnitude <Alt_M> The {Star Magnitude} icon (keystroke <Alt_M>) is two stars of different sizes in the same color. The button toggles the display of star magnitudes on the sky panel. Magnitudes are in the range -1.0 to +4.0 are display as filled circles with a radius proportional to brightness. That is, the brightest star, Sirius, is biggest. Only those ranges enabled in the [Star Magnitude] options menu are displayed. 3.1.4 Star Color <Alt_C> The {Star Color} icon (keystroke <Alt_C>) is two stars of different sizes in different colors. The button toggles the display of star colors on the sky panel. Stars are displayed by both magnitude and color index (OBAFGKM). The correspondence between spectral type and screen color in 16-color graphics modes is: Spectral Class Screen Color O very blue Light Blue B blue Light Cyan A green Light Green F white White G white-yellow Yellow K orange-red Light Red M red Red Only those spectral classes enabled in the [Star Color] options menu are displayed. 3.1.5 Animation <Alt_A> The animate {Big A} icon (keystroke <Alt_A> toggles continuous time-stepping with current time-step. All display objects (Sun, Moon, planets, stars) are redrawn as single pixels to mark track through the sky panel. If the step is an integral number of sidereal days the stars remain static so ASTRO does not have to update their positions for short- term simulations. There is little or no overhead involved in having the stars displayed as a backdrop to solar system animations if a sidereal day is used as the time-step. 3.1.6 Grids <Alt_G> The {Grids} icon (keystroke <Alt_G>) is an open circle with two mutually perpendicular diameters drawn. The button toggles the display of the altitude-azimuth grid (concentric circles and radial lines drawn every 15 degrees) on the sky panel. Note: the time to redraw the grid may be several seconds on slow cpus. 3.1.7 Lines and Planes <Alt_L> The {Lines} icon (keystroke <Alt_L>) is an open circle with an arc passing through the horizontal diameter. The button toggles the display of the lines representing the ecliptic and celestial equators and the galactic plane on the sky panel. Only those planes that have been "turned on" in the [General] options menu are displayed. 3.1.8 Text <Alt_T> The {Big T} icon (keystroke <Alt_T>) toggles the display of text (azimuth directions and object labels) in the GUI. The {Text} button will eliminate all text from the sky panel. Note: selective text elimination is not possible in this version of ASTRO. 3.1.9 Daylight Savings <Alt_D> The {Daylight_Savings} icon (keystroke <Alt_D>) is a circle with multiple short rays extending from the circumference. The button toggles between local standard time (LST) and local daylight savings time (LDT) for data entered through the [Date and Time] selection in the [Data] menu. The default is LST. 3.2 Time-Stepping and Animation ASTRO offers a great deal of flexibility in single-stepping and multiple-stepping (animation) through time. The program remembers the sense (forwards or backwards) and size of the current time-step (solar hour, day, month, year or sidereal day or 100,000 days) and uses it for animation. The time-step on startup is one sidereal day. The time-step icons are located in the lower left hand corner of the GUI and comprise 6 buttons. The arrow head icon of the current time step is highlighted in the GUI. The icon between the two pairs of up and down arrows indicates the size of the solar and sidereal time-step: {HH} for hours (the solar time-step default), {DD} for days, {MM} for months, {YY} for years, {*} for sidereal days (the sidereal time-step default) and {Three_*} for 100,000 sidereal days. 3.2.1 Solar Time Step <Hh> or <Dd> or <Mm> or <Yy> The solar time-step can be changed from hours to days to months to years and back to hours by clicking on the {Double Letter} icon between the up and down arrows. Alternatively, <H> or <h> will set the solar time-step to hours, <D> or <d> to days, <M> or <m> to months and <Y> or <y> to years. The step is forwards if the {Up_Arrow} is highlighted ("turned on") or the step is set by an upper case letter. The step is backwards if the {Down_Arrow} is highlighted or the step is set by a lower case letter. Clicking on the arrows causes the display to be erased and redrawn at the new time. 3.2.2 Sidereal Time Step <Ss> or <Ll> The sidereal time-step can be changed from days to 100,000 days and back to days by clicking on the {*} icon between the up and down arrows. Alternatively, <S> or <s> will set the sidereal time-step to days (S-for-Short), <L> or <l> will set the sidereal time-step to 100,000 days (about 273 years) (L-for-Long). The step is forwards if the {Up_Arrow} is highlighted or the step is set by an upper case letter. The step is backwards if the {Down_Arrow} is highlighted or the step is set by a lower case letter. Clicking on the arrows causes the display to be erased and redrawn at the new time. 3.2.3 Animation Toggle <Alt_A> The animate {Big A} icon (keystroke <Alt_A> toggles continuous time-stepping with current time-step. All display objects (Sun, Moon, planets, stars) are redrawn as single pixels to mark track through the sky panel. Note: if the step is one sidereal day (or a small multiple) the stars remain static so ASTRO does not have to update their positions for short-term simulations. For the long sidereal time-step, ASTRO computes and animates the proper motions of the stars. On machines without a math co-processor, the animating large numbers of stars is a slow process. If the zoom option is used, the number of floating-point operations per step is considerably reduced and the animation will proceed a little more quickly. 3.2.4 Stop and Redraw <Esc> Halt animation and redraw sky panel for final positions of all display objects (Sun, Moon, planets, stars). To save tracks, stop and start animation with the <Alt_A> toggle. 3.3 Pan and Zoom The pan and zoom icons are located in the lower right hand corner of the control panel to the right of the time-step icons. 3.3.1 Pan Up <Up_Arrow> The pan up icon {Up_Arrow} (keystroke <Up_Arrow>) pans the display up one eighth screen. 3.3.2 Pan Down <Down_Arrow> The pan down icon {Down_Arrow} (keystroke <Down_Arrow>) pans the display down one eighth screen. 3.3.3 Pan Left <Left_Arrow> The pan left icon {Left_Arrow} (keystroke <Left_Arrow>) pans the display left one eighth screen. 3.3.4 Pan Right <Right_Arrow> The pan right icon {Right_Arrow} (keystroke <Right_Arrow>) pans the display right one eighth screen. 3.3.5 Zoom Up <+> The zoom up icon {Big +} (keystroke <+>) zooms the screen by adding one to the current zoom factor. That is, the zoom factor will increase from x 1 to x 2 to x 3 to x 4 and so on with each mouse-click or keystroke. The maximum zoom factor is x 16. 3.3.6 Zoom Down <-> The zoom down icon {Big -} (keystroke <->) zooms the screen down by subtracting one from the current zoom factor. That is, the zoom factor will decrease from x 16 to x 15 to x 14 to x 13 and so on with each mouse-click or keystroke. The minimum zoom factor is x 1. 3.3.7 Restore Pan-Zoom <Home> or <Alt_H> The zoom home icon {Big H} (keystroke <Home> or <Alt_H>) restores the zenith point to the centre of the display and the screen zoom factor to its default value of x 1. 3.4 Save Screen Output <Alt_O> The {Printer} icon (keystroke <Alt_O>) is a stylized picture of a printer. The button causes the current screen to be written to a file in Epson, Hewlett-Packard, Postscript or GIF format, depending on the settings in the [Output] menu. ASTRO names files astroxxx.prn, astroxxx.pcl, astroxxx.eps and astroxxx.gif as appropriate, where xxx represents three decimal digits starting at 000 and incrementing by one each time a file dump is requested. ASTRO will write up to 100,000,000 files of each extension before astro000.??? is overwritten! Note: No check is made to see if disk space is available for a file. If the file output cannot be completed, the file is deleted but no warning message is given. In some circumstances, ASTRO will fail to detect the "disk full" condition and "lock-up". The checking necessary to avoid this eventuality slows the process of writing a large EPS file and it is not included in ASTRO. The user is responsible for ensuring adequate disk space is available. In this regard, GIF files (5- 8K) require much less space than printer screen dump files (37-45K). Postscript files may be very large (600K+). 3.5 Exit to Text_Menus <Alt_X> or <Alt_Q> The {Big Q} icon (keystroke <Alt_Q> or <Alt_X>) exits to the text-menu interface. ASTRO : APPLICATIONS AND EXAMPLES 4.0 Introduction This section is step-by-step guide to the Astronomy Laboratory Exercises for Science 280 at Athabasca University. 4.1 Motions of the Sun and Moon Since ancient times, people have been interested in the motions of the Sun and Moon. In this exercise we will determine the orbital period of the Moon relative to the background of fixed stars and examine the variations in the altitude of the Sun during the year. It is NOT necessary to read the file "YALE.BIN" for this exercise. Users may optionally employ the stars as a fixed background. 4.1.1 Orbital Period of the Moon The orbital period is the time required for an object to travel 360 degrees around the sky. Over time, the Moon traces a great circle on the heavens when viewed against the background of fixed stars. To fix the stars, we view the sky at the same sidereal time on each successive day. Start up ASTRO with the default data. Since we are interested in the Moon alone, go to the [Options] pulldown menu and select [Solar System]. Click the mouse on the [Sun] selection or enter <S> to turn off the Sun display. On the [General] options menu make sure that only [Sun and Moon] is tagged. Check the Space-Time Coordinates information panel from the [Defaults] selection on the [Info] pulldown to ensure that we are viewing the southern horizon (azimuth 180 degrees). Change the latitude and longitude in the [Data][Position] menu to reflect your location. The default is Athabasca, Alberta. Now we are ready to enter the graphical display, so select [Plot_Star_Map] from the [Plot] pulldown menu. The Moon should be visible on the sky panel at roughly 3 o'clock (if you are at a similar lat,long to the default). MOUSE: Position the mouse cursor as near as possible to the centre of the square representing the Moon and read off the altitude and azimuth from the button panel on the left of the screen. KEYS: Enter <Alt_G> to display the altitude-azimuth grid. Both the radial lines (azimuth) and the circles (altitude) are drawn every 15 degrees. The outer circle is at altitude zero, so estimate the altitude by counting the number of complete and fractional 15 degree intervals to the Moon. The radial lines of azimuth increase counter-clockwise from zero in the North. Estimate the azimuth of the Moon by counting the number of complete and fractional 15 degree intervals. (Mouse users can also carry out this exercise to check their earlier result.) To step through time, we must first select a suitable time interval (sidereal days to fix the stars). The default time interval is one sidereal day (notice that the {Up_Arrow} above {*} on the button panel is "on". Write down the time displayed on the button panel. Click on the {Up_Arrow} button above the {*} icon (keystroke <S>) and the sky panel will redraw one sidereal day forward in time. Check the time display again and confirm that 1 sidereal day is 23h 56m 04s. Now click on {Down_Arrow} or type <s> to go back to the original time. Notice that the {Down_Arrow} is now "on". ASTRO steps in time by the amount and in the direction of the "on" arrow so starting animation now will move backwards in steps of sidereal days. To measure the orbital period of the Moon, we need to measure the time required for the Moon to move 360 degrees across the sky. Click on the {Up_Arrow} or type <S> several times and watch the Moon's position move towards the right of the screen (westward). When the Moon is reasonably close to the edge of the display, step once more or until the Moon disappears over the western horizon, then move one step in the opposite direction to make the Moon reappear with the {Up Arrow} "on". Record the time from the button panel and estimate the azimuth and altitude of the Moon as accurately as you can. Now step forward in time by sidereal days (counting steps) until the Moon approaches and disappears over the eastern horizon. Continue to step forward until the Moon reappears from the west and record time and azimuth again. We have now measured the time for the Moon to move through an arc of close to 360 degrees. The number of "clicks" or <S>'s is the number of sidereal days (or use the information panel time difference in solar days). Advance (or retreat) one step to "bracket" your original altitude azimuth coordinates and estimate the fractional part of a day to reach the identical point in the sky. We can now repeat the exercise using ASTRO's animation option. First, step back to where you started and click on the {Up_Arrow} or type <S> to set the stepping direction to forwards. Click on {Big Q} (keystroke <Alt_Q> or <Alt_X>) to return to the text menu. From the [Options] menu (keystroke <Alt_O>, select [Animation] (keystroke <A>). Set the number of steps to the nearest whole day past your estimate (or 30). Now select [Plot Star Map] again from the [Plot] pulldown menu to return to the GUI. Click on the {Big A} or type <Alt_A> to animate the display. If you have a fast computer, the track on the Moon will rapidly trace out the successive positions of the Moon tracing a great circle across the sky panel. Notice that two dots appear on the path to the west and the east of the Moon square. Each dot is one-sidereal day along the orbital path and it is easy to estimate the fractional part of a day to reach the starting position from this display. 4.1.2 Changes in the Altitude of the Sun Since ancient times, it has been known that the altitude of the Sun at noon varies with the seasons. In this exercise, we will investigate the changes in the altitude of the Sun at noon over the course of a year. Start in the text-menu and reset the observer space-time coordinates in the [Data] menu to the default (or any suitable value) using the [Position] and [Date and Time] selections. coordinates to the default (or any suitable value). Set the time to 12:00:00. Select [Solar System] in the [Options] menu and make sure the Sun is tagged and the Moon is untagged. In the [General] options menu, check that [Sun and Moon] is tagged and [Planets] is untagged. Set the number of animation steps to 365 or just a few more days. Now open the GUI by selecting [Plot Star Map] from the [Plot] pulldown menu. The screen should display only the zenith point and a square (yellow if you have color) for the Sun. If you used the default data, the Sun is near the southern horizon. If you do not have a mouse, turn on grid lines with {Grid} (keystroke <Alt_G>) to facilitate estimation of angles. Click on the {double letter} icon until it reads {DD} (keystroke <D>). Use the {Up_Arrow} and {Down_Arrow} buttons (or <D> and <d> keys) to set start-time and the time-step to advancing solar days. Click on {Big A} (keystroke <Alt_A>) to start animation and the path of the Sun at noon will be traced out as a figure-of-eight loop. Use {Big A} or <Alt_A> to stop and restart the animation when the loop is at its highest and lowest altitude. You may want to repeat the exercise with the number of steps set to 91 or 92 in the [Options][Animation] menu and the start date set to an equinox or solstice. ASTRO will then step (approximately) between equinoxes and solstices with the <Alt A> toggle. 4.2 Planetary Motions Early models of the solar system had difficulties in explaining the motions of planets, in particular, retrograde motions. In this exercise we will investigate the motions of the inner and outer planets and determine the orbital period of one of the planets. We will also add the stars to the display. 4.2.1 Apparent Star Motions Start in the text-menu and reset the observer space-time coordinates in the [Data] menu to the default (or any suitable value) using the [Position] and [Date and Time] selections. Select the [General] options menu, untag the [Sun and Moon] and [Planets] selections. In the [Data] menu, select [Star Catalog] and read the data file "YALE.BIN" into Astro. "YALE.BIN" contains information for 526 stars. Now open the GUI by selecting [Plot_Star_Map]. Set a forward time-step of one solar hour. Click on {Star_Magnitude} (keystroke <Alt_M>) to display the stars. If you used the default settings, Sirius should visible as a large circle marked with a cross near the southern horizon. Orion should be NW of Sirius and the Big Dipper should be N and E of the zenith point. Click on {Big A} (keystroke <Alt_A>) to animate the stars. After a time, the rotation about Polaris should become apparent. The stars return to the same position in the sky once every sidereal day. Thus, when we observe the sky at intervals of whole sidereal days, the stars appear frozen in place. 4.2.2 Retrograde Planetary Motion Start in the text-menu and reset the observer space-time coordinates in the [Data] menu to the default (or any suitable value) using the [Position] and [Date and Time] selections. Select [Solar System] in the [Options] menu and untag all the planets except one. Now select the [General] options menu, untag the [Sun and Moon] selection and tag [Planets]. In the [Data] menu, select [Star Catalog] and read the data file "YALE.BIN" into Astro. "YALE.BIN" contains information for 526 stars. Now open the GUI by selecting [Plot_Star_Map]. Set a forward time-step of one sidereal day (this should be the default). Click on {Star Magnitude} (keystroke <Alt_M>) to display the stars as a backdrop to the planetary motions. Click on {Big A} (keystroke <Alt_A>) to animate your chosen planet. Let the animation run for several years then examine the plot for evidence of retrograde motion. You can continue the animation for another 100 steps with {Big A} or <Alt A>. 4.2.3 Orbital Period of the Planets Start in the text-menu and reset the observer space-time coordinates to the default (or any suitable value). Select [Solar System] in the [Options] menu and untag all the planets except one. Make sure you have read the star catalog "YALE.BIN" so that you can display the stars as a background to your observations. Select either Jupiter, Saturn, Uranus, Neptune or Pluto. Now select the [General] options menu, check that the [Sun and Moon] selection is untagged and that [Planets] is tagged. Now open the GUI by selecting [Plot_Star_Map]. If the planet is not visible, advance by months until it appears on the display. Try to get the planet near azimuth 180° as a starting position. Set a forward time-step of one sidereal day by stepping back then forward. Record the time and date. Click on {Big A} (keystroke <Alt_A>) to animate your chosen planet. Let the animation run for one orbital period. It will stop every 100 steps (the default). Record the time at which the planet passes it's starting position. You may want to change the number of steps default to get a more accurate estimate or use <Alt_A> to stop the animation. Note: the orbital periods of the outer planets are many years. It may be useful to set the number of steps to 366, 732, 1099, 1465, 3662 or some other near multiple of a solar year (366.2442 sidereal days). The best optimum time-step will depend on your choice of planet. Hint: if you have an 8088 cpu, pick Jupiter. 4.3 Motions of the Stars The stars are at such great distances from the Earth that they are apparently immobile over periods of centuries. However, the stars themselves are actually moving through space. The objective of this exercise is to study the proper motions of the stars. To do this, we must plot the position off the stars over several thousand years. Start in the text-menu and reset the observer space-time coordinates in the [Data] menu to the default (or any suitable value) using the [Position] and [Date and Time] selections. Select the [General] options menu, untag the [Sun and Moon] and [Planets] selections. In the [Data] menu, select [Star Catalog] and read the data file "YALE.BIN" into ASTRO. "YALE.BIN" contains information for 526 stars. Now open the GUI by selecting [Plot Star Map]. Choose an area of the sky covering about 45 degrees of altitude and azimuth space. Use the arrow keys and the <+> key to pan and zoom this region to fill the screen. If you have a slow computer, do not display any stars when you do this. You may want to turn on the {Grid} button (keystroke <Alt_G>) as a guide. The grid is also valuable when you come to quantify star motions. IMPORTANT NOTE: you must turn the grid on BEFORE you start star animation. The display will be redrawn if you attempt to add a grid later and all star tracks will be lost. Now display the stars using the {Star Color} button (keystroke <Alt_C>. Click the {*} button until the {three asterisk} icon appears (keystrokes <L> or <l>). The time-step is now 100,000 sidereal days or about 273 years. Step forward {Up_Arrow} or <L> to set the animation step and direction for observing star motions. At some stage you will need to estimate the altitude-azimuth coordinates for all the stars visible on the zoomed display (on average there will be about 10). Use the mouse cursor or the grid lines to do this. Now click {Big A} or <Alt_A> to begin animation. Trails will eventually appear tracing the proper motions of the stars. With the default number of steps (100), the animated period will be 27,300 years, enough to estimate the magnitude of many proper motions. Stop the animation every 5000 years or so <Alt_A>, read the date display, and measure the altitude and azimuth of the "end" points of the trails. Use the mouse or the grid lines to make these estimates. You can estimate the angular separation of the initial and final positions of the stars using: cos(ds) = sin(h0).sin(h1) + cos(h0).cos(h1).cos(A0 - A1) where (h0, A0) and (h1, A1) are the altitude-azimuth coordinates of the initial and final star positions and (ds) is the angular separation of the points. If the star moves approximately parallel to the azimuth lines, ds ≈ A0 - A1; if the star moves approximately parallel to the altitude lines, ds ≈ h0 - h1. The proper motion in seconds of arc per year is (ds/dt) / 3600, where ds is in degrees and dt in years. Estimate the proper motions of as many stars as possible in your chosen field of view. Now repeat the exercise with the whole sky visible. Is there any correlation between proper motions and spectral class? Why might such a relationship be suspected? Is there any evidence of groups or clusters of stars with similar motions? Experiment with ASTRO to investigate these possibilities. 4.4 Distances to the Stars The distances to main sequence stars can be estimated from their color indices and apparent magnitudes. The objective of this exercise is to estimate the distances to those stars visible from your location on the Earth at the present time. Start in the text-menu and reset the observer space-time coordinates in the [Data] menu to your local position and time using the [Position] and [Date and Time] selections. Select the [General] options menu, untag the [Sun and Moon] and [Planets] selections. In the [Data] menu, select [Star Catalog] and read the data file "YALE.BIN" into ASTRO. "YALE.BIN" contains information for 526 stars. Now open the GUI by selecting [Plot Star Map]. The {Star Color} button (keystroke <Alt_C>) will display the stars by color and magnitude. To estimate distance (r parsecs) we need the apparent magnitude (m) and the absolute magnitude (M), then: log(r) = 1 + (m - M )/ 5 The color index or spectral class of a star can be used to estimate absolute magnitude using charts or less accurately using the following table (prepared for main sequence stars) : ┌────────────────┬──────────────┬────────────────────┐ │ Spectral Class │ Color │ Absolute Magnitude │ ├────────────────┼──────────────┼────────────────────┤ │ O │ blue │ < -3.5 │ │ B │ blue-green │ -3.5 to 0.6 │ │ A │ green │ 0.6 to 3.2 │ │ F │ white │ 3.2 to 4.3 │ │ G │ white-yellow │ 4.3 to 6.2 │ │ K │ orange-red │ 6.2 to 9.5 │ │ M │ red │ > 9.5 │ └────────────────┴──────────────┴────────────────────┘ To isolate stars with a particular apparent magnitude and color index, we must return to the text- menu {Big Q} or <Alt_X> or <Alt_Q>. From the [Options] menu first select [Star Magnitude] and untag all but one magnitude class. Hit <Esc> to exit the menu and select [Star Color]. Again leave only one option tagged. Now return to the GUI via the [Plot Star Map] selection. The only stars plotted will be those meeting the color/apparent magnitude criteria you chose. You may not see any stars if you chose extreme values for your classes (< -1 or > 4) and (O). If the stars are main sequence stars they will be approximately the same distance from Earth. You can estimate that distance using the formula. Notice that different combinations of apparent magnitude and color index can give the same distance, for example ( F, 3.0 to 4.0) and (B, -1.0 to 0.0). ASTRO will generate (7 x 7 = 49) groups for various combinations of apparent magnitude and spectral class. Calculate a value of r for each of these groups. Select and plot sets of stars for a range of distances. 4.5 Distribution of Stars in the Galaxy The Milky Way Galaxy (our galaxy) was found to have a non-spherical shape by Sir William Herschel. The discovery was made by counting the number of visible stars in different directions in the sky. The objective of this exercise is to repeat this important observation for ourselves. For this we need a view of the sky in the direction of the galactic centre. Such views are best obtained in the southern hemisphere (the galactic centre is just visible on the extreme southern horizon from the 49th parallel). Start in the text-menu and reset the observer space-time coordinates in the [Data] menu to the position of Sydney, Australia (latitude -34°, longitude 209°). Choose a night in the Australian winter (our summer) when the galactic centre is overhead. Select the [General] options menu, untag the [Sun and Moon] and [Planets] selections. Untag both [Equator] selections leaving the [Galactic Plane] tagged. Make sure you have read the data file "YALE.BIN" using the [Star Catalog] selection in the [Data] menu. Now open the GUI by selecting [Plot Star Map]. Turn on the altitude-azimuth grid display with the {Grid} button (keystroke <Alt_G>). Display the stars with the {Star Magnitude} (keystroke <Alt_M>) or {Star Color} button (keystroke <Alt_C>). Turn on the galactic plane display with the {Lines} button (keystroke <Alt_L>) and use the time-arrow hour button or keys (<H> and <h>) to get the galactic plane to (approximately) pass through the zenith point. The galactic pole marked NGP or SGP will be close to the horizon and the galactic centre close to the zenith point. Now select the grid boxes that lie on the galactic plane around the galactic centre and count the number of stars. The pan- zoom buttons or keys may make this task much easier. For each 15 degree grid box, count and record the number of stars and record the azimuth-altitude coordinates of a corner (as identification). There are no grid lines around the zenith point so you will have to estimate the extrapolated position of the radial lines for these. Now use the time-arrow hour keys to move the south galactic pole (SGP) to near the zenith point and count the star density again. Now we need to repeat the exercise for the opposite direction. Exit to the text-menu interface and choose a point opposite Sydney in the northern hemisphere (latitude +34, longitude +29). This point is in the North Atlantic, south of the Azores. Here the galactic anti-centre is overhead in winter. Repeat the counting exercises, this time move the north galactic pole to the zenith point. Do you agree with the conclusions of Sir William Herschel? ASTRO and other similar programs make it possible to observe the sky from many different locations on the surface of the Earth. As with all computer models, you should attempt to verify your observations whenever possible by direct observation. Plan your next vacations in Australia and the Azores! ASTRO: DEVELOPMENT HISTORY 5.0 Introduction ASTRO 2.0 comprises approximately 10,000 lines of C source code developed at Athabasca University between mid-March and mid-June 1992 (approximately 750 man-hours of code development and documentation). Much of the code (mouse, windows, buttons, icons, help, GIF, and printer support) is readily re-useable for similar scientific and technical applications. 5.1 Star Catalog File Format The format of the file "YALE.BIN" is as follows. Each star record comprises six 4-byte IEEE single precision floating point numbers representing right ascension (radians), declination (radians), magnitude, color index, rate of change of right ascention (radians per epoch), and rate of change of declination (radians per epoch). 5.2 Version 1.0 ASTRO Version 1.0 was developed in 1988 by Tony Willis with the following features: - CGA 2-color graphics support only - Menu-driven configuration - No built-in hardcopy or screen save support - Fixed resolution Alt/Az display - Sun, Moon and planetary motions - Star motions including proper motions - 526 star catalog 5.3 Version 2.0 ASTRO Version 2.0 represents a major upgrade undertaken by Malcolm Reeves in 1992. The significant additional features incorporated in ASTRO now include: - VGA, EGA, CGA, ATT support in 2-color and 16-color modes - Extended user-configuration pulldown menu system - Context sensitive on-line help menus and windows - Default configuration at start-up - Built-in hardcopy support for IBM/Epson, Hewlett-Packard and Postscript printers - Screen save support in GIF format files - Icon-button-driven graphical user interface (GUI) - Microsoft-compatible mouse support for menus and GUI - Time-step animation with trails for solar system objects and stars (including proper motions) - Full pan-zoom capability for graphics screen - 30+ page User Manual A number of technical programming improvements have also been made to the C language code to make the program faster, smaller, more portable and easier to maintain and upgrade: - Reduced memory and disk space requirements - Faster arithmetic and graphics performance - Increased portability of source code between MS-DOS compilers - Elimination of all calls to third-party graphics and windows routines 5.4 Future Development Future upgrade possibilities (in order of ease of implementation): - Extend star database - User-saved configuration file for startup - Real-time (system) clock option - RA/Dec co-ordinate display option - Interactive measurement of angular distances - Pick/find star name capability - Keystroke support for cursor on graphics screen - Support constellations - Provide comet and deep sky objects databases - Eliminate text-menus (make application 100% graphical) - Integer arithmetic option (for speed without 80x87) 5.5 Version 2.xx Revisions and Changes 28 May 1992 First release of version 2.00 4 June 1992 Version 2.01 Added gif file dump support. Added all and none options to [Solar System Options], [Star Color Options], and [Star Magnitude Options]. Revised 5 time-step buttons on GUI to 2 buttons for solar and sidereal time. Added [Animation Options] to allow user to set number of steps Fixed slow scrolling of help files with mouse. Fixed bug causing mouse to be re-initialized every step in animation mode. Added text-menu exit via cursor keys. Added [Options] pulldown menu, old [Plot] menu. Information panels are not displayed at start up (there are too many). Added [Defaults] selection in [Info] pulldown to allow selective display of information panels. Modified user manual (revision 1.09) and on-line help routines to reflect changes. 15 June 1992 Version 2.02 Added support for IBM/Epson, Hewlett-Packard and Postscript printers. Added [Output] selection to [Options] menu. 25 June 1992 User manual (revision 1.10) and on-line help revised. 8 July 1992 Source code documentation (revision 1.0) completed. Minor revisions to user manual (revision 1.11)