Garbo/Garbo.cdr/pc/source/star.lzh/star.24

Text File | 1990-04-06 | 35.4 KB | 941 lines

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X.ND
X
X.ds St Astronomy\ Tools
X.OH '\\*(St''%'
X.EH '%''\\*(St'
X.PP
X.PP
X.PP
X.PP
X.PP
X.PP
X.PP
X.PP
X.sp 10
X.ce
X.ps +10
X.ce
XAstronomy\ Tools
X.ps -10
X.sp 2
X.ce
XCraig\ Counterman
X.PP
X.bp
XCopyright \(co 1990 Craig Counterman.  All rights reserved.
X.bp
X.PP
X.PP
X.PP
X.PP
X.PP
X.PP
X.bp
X.NH
XIntroduction
X.br
X.PP
XThese programs are intended to assist observational astronomers.
X.PP
XStarchart produces astronomical charts from a variety of databases,
Xproducing output for, in rough order of quality, PostScript, X11,
Xsunview, Atari St, IBM PC, X10, tektronix, unix plot, HP laserjet, and
Xtty displays, on Unix, vms and other systems.  It is straightforward to
Xwrite drivers for other output devices.  Observe is a multifunction
Xprogram for use in planning an observing session.  It calculates the
Xpositions of planets and their satellites, asteroids and comets,
Xcalculates rising and setting times, and much more.
X.PP
X.PP
XThis software may be redistributed freely, not sold.
X.PP
XNo representation is made about the suitability of this
Xsoftware for any purpose.  It is provided "as is" without express or
Ximplied warranty, to the extent permitted by applicable law.
X.PP
X.sp 2
X.SH
XDISCLAIMER\ OF\ WARRANTY
X.br
X.PP
XThe author  disclaims all warranties  with regard to  this software to
Xthe   extent  permitted  by applicable   law,  including all   implied
Xwarranties  of merchantability  and  fitness. In  no event shall   the
Xauthor be liable for any special, indirect or consequential damages or
Xany  damages whatsoever resulting from  loss of use, data or  profits,
Xwhether in an action of contract, negligence or other tortious action,
Xarising  out of  or in connection with the  use or performance of this
Xsoftware.
X.PP
X.PP
X.PP
X.NH 2
XWhat\ the\ Programs\ Do
X.br
X.PP
XSeveral programs are included in this package, all intended to aid
Xobservational astronomers.  The \fBobserve\fR program calculates positions
Xof moving objects and helps in planning an observing session.  There are
Xseveral starchart programs for preparing astronomical charts; there is a
Xseparate program for each output device.  There are also several support
Xprograms which operate on data files for these programs.
X.PP
XStarchart programs are quite general star map drawing programs and
Xhave many potential uses, but their unique utility is in preparing
Xcustom charts for particular observing projects, finding charts, and a
Xpages that can be put in observing notebook and annotated at will.
X.PP
XThe \fBobserve\fR program provides many facilities of use in planning
Xan observing session.  It can generate ephemerides of planets, minor
Xplanets, and comets, and puts the coordinates in files to be used with
Xstarchart programs.  It calculates the approximate altitude and azimuth
Xof obects at sun rise and set and morning and evening twilights.  It can
Xcalculate positions of the major satellites of Jupiter and Saturn.  Of
Ximportance to observers is the generation of the timetable of events for
Xa night.
X.PP
XOther programs are provided to facilitate the use of these programs.
X.PP
X.NH 2
XThe\ Sky
X.br
X.PP
XThere is a sky.  There are things in the sky.  The starchart programs
Xdraw maps of things in the sky.  The \fBobserve\fR program helps you plan
Xto look at things in the sky.
X.PP
XThe things in the sky include stars, planets, nebulae, clusters of
Xstars, and galaxies. For thousands of years, people have grouped the
Xstars in the sky into patterns, and constellations.  More recently, the
Xsky has been divided into areas based on these constellations.  For
Xhundreds of years, astronomers have used a latitude-longitude grid for
Xdefining the locations of celestial objects.  The longitude is usually
Xreferred to as right ascension or RA, the latitude is the declination or
XDEC.  Through the year, the sun follows a path in the sky, called the
XEcliptic, which is the plane of the earth's orbit.  Other planets in the
Xsolar system are roughly in this plane.
X.PP
XThe locations of stars, nebulae, clusters, and galaxies have been
Xtabulated for hundreds of years.  These programs use computerized forms
Xof such databases.
X.PP
X.NH 2
XCoordinates
X.br
X.PP
XYou should be familiar with the method of specifying a location on the
Xsurface of the earth: two coordinates are used: latitude north of the
Xequator and meridian of longitude east of Greenwich.  A similar system
Xis used to specify the locations of points in the sky.  the meridians
Xare called right ascension, and the latitude is called declination.
XRA is measured from the point at which the sun crosses the equator in
XMarch.  It is measured in hours, with 15 degrees = 1 hour.
X.PP
XThere are two other coordinate systems commonly used in addition to
XRA--dec.  These apply only to a particular observation location and
Xtime.  The first of these is Hour angle -- declination.  It is similar
Xto R.A.--declination, but instead of R.A., the angle is measured west
Xfrom the line from north to south passing directly overhead.  The second
Xis altitude -- azimuth (alt--az): altitude in degrees above the horizon
Xand azimuth in degrees east from north.
X.PP
X.NH 2
XEpoch\ and\ Equinox
X.br
X.PP
XThe coordinates of a ``fixed'' object are actually only approximately
Xconstant.  Two factors change the coordinates in R.A. and declination.
X.PP
X.NH 3
XProper\ Motion\ and\ Epoch
X.br
X.PP
XFirst, stars (and other galactic objects) are not fixed in space.  The
Xsun and stars all move.  Only the closer stars move significantly, but
Xcloser stars are also brighter, so this is an important effect.  The
X\&\fIepoch\fR is the time for which the coordinates are valid including
Xthe effects of this \fIproper motion\fR.
X.PP
X.NH 3
XPrecession\ and\ Equinox
X.br
X.PP
XThe second and more important factor is that the R.A.  and dec.
Xcoordinate system changes: the north pole and thus the equator change
Xdue to \fIprecession\fR.  R.A.  changes as the equator moves and changes
Xthe point at which the sun crosses the equator.  The \fIequinox\fR date,
Xor \fIequator and equinox\fR is the time at which the coordinate system
Xis valid.  Equinox 2000.0 and 1950.0 are commonly used coordinate
Xsystems.  The equator and equinox of the date is also occasionally
Ximportant.
X.PP
XThe starchart programs use data in equinox 2000.0 coordinates.
X.PP
X.NH 2
XAdditional\ Corrections\ to\ Positions
X.br
X.PP
XPrecession and epoch were discussed above.  In addition there are
Xsmaller effects which must be considered for precise astrometry.  These
Xinclude effects of motion about the earth-moon barycenter, light travel
Xtime, nutation, and aberration of starlight.
X.PP
X.NH 2
XMagnitudes
X.br
X.PP
XMagnitudes are defined with respect to standards.
X.PP
XObjects emit photons.  The number of photons per second observed from an
Xobject under given conditions and equipment is the intensity of light.
XA brighter object emits more photons.  The difference in magnitudes
Xbetween two objects is -2.5 times the log (base 10) of the ratio of
Xintensities, i.e.
Xm = m_std - 2.5 log(s/s_std)
X.PP
XMagnitudes are measured in different ways.  The most important are
Xvisual, photographic, and photometric.  Visual and photographic
Xmagnitudes are measured using those methods to estimate relative
Xmagnitudes.  Photometry is the counting of photons received from
Xobjects.  Standard filters are generally used.  The most common set is
XUBVRI, Ultraviolet to Infrared.  The V filter approximates the response
Xof the eye, while the B filter is approximately the response of
Xphotographic film.
X.PP
XFor a magnitude number to be truely meaningful, the system used must be
Xspecified.  Generally V or visual may be assumed.
X.PP
XFor many objects (V-B), that is the magnitude measured photometrically
Xwith the V filter minus the B magnitude, indicates the color of the object.
X.PP
X.NH 2
XTime\ and\ Date
X.br
X.PP
XTime is a very complex subject.
X.PP
X.NH 3
XTime
X.br
X.PP
XTime systems include UT (= UT1), UT0, TA1, and UTC.  These times may
Xdiffer by a second or so.  They are based on the rotation of the earth.
XAs the earth slows, and since the day is not \fIexactly\fR 86400 seconds
Xlong, leap seconds are occasionally inserted.  They are all
Xapproximately the time at 0 degrees longitude.  Most astronomical times
Xare quoted in UT (universal time).  The differences are rarely critical
Xfor amateurs.
X.PP
XAnother significant time system TDT (formerly ET), and TBT.  TDT or
XTerrestrial Dynamical Time is based on the orbits of the planets, as is
XTBT or Terrestrial Barycentric Time (based on the center of motion of
Xthe earth-moon system).  These times currently differ from UT by about a
Xminute.  TDT is the time which should be used for planetary calculations.
X.PP
XTime zones relate local time to the time at 0 longitude.  Be aware that
Xthere are some fractional time zones in the world.  Daylight savings
Xtime (or ``summer'' time) is an additional complication.  You should
Xlearn how your time zone is related to the time at 0 longitude (UT or
XGMT).  EST is 5 hours behind, EDT is 4 hours behind.
X.PP
XThese times are all related to the position of the sun: the sun should
Xbe overhead at about noon local standard time.  A different time is
X\&\fIsidereal\fR time, based on the positions of the stars overhead.  Two
Ximportant sidereal times are GST or Greenwich Sidereal time, and LST or
Xlocal sidereal time.
X.PP
X.NH 3
XDate
X.br
X.PP
XCalendars are confused and confusing.  To avoid confusion between the
Xmany calendars in use historically, JD \fIJulian date\fR is used.  The
XJD 0 is a day more than 4000 years BC (BCE).
X.PP
X.NH 2
XAtmospheric\ Effects
X.br
X.PP
XRefraction affects alt-az  coordinates: light from objects are bent
Xby the atmosphere, making them appear higher in the sky than they would
Xif there were no atmosphere.  The error can reach 34 minutes of arc at the
Xhorizon.  Extinction, absorption and scattering make objects fainter the
Xmore atmosphere the light from them must pass through (that is, the
Xcloser to the horizon they are).  Other effects of the atmosphere are
Xseeing (the effect which produces twinkling of stars), scintillation,
Xairglow, and of course light pollution.
X.PP
X.NH 2
XElements\ of\ an\ Observing\ Session
X.br
X.PP
XTo avoid frustration and ensure meeting goals you should plan your
Xobserving session in advance.  More serious the goal the more carefully
Xyou should plan.  At least, having a plan may help you avoid wondering
Xwhat to do next on a clear night.
X.PP
XA timeline of events ensures that an object will be observable, and
Xhelps schedule a night to observe all objects when they are well placed.
XThe events are sun and moon rise and set, astronomical twilight, and the
Xrising, setting and transit times of objects.  In addition, objects
Xshould be observed when possible when they are above 30 degrees above
Xthe horizon, or at least above 20 degrees.  These times should also be
Xnoted in the time line.
X.PP
XCharts are used in identifying planets, asteroids, and comets, and
Xfinding objects.  For very faint objects, a photographic atlas of the
Xarea should be xeroxed.
X.PP
XA notebook is an important part of observing.  It can be of scientific
Xnotebook quality, or a simple note of what objects you observed and how
Xthey looked.  Starchart programs may be used to produce finder charts
Xwhich you can annotate and keep in a notebook.
X.PP
X.NH 2
XHints
X.br
X.PP
XUse grep, awk and shell scripts.  Unix tools can be very helpful in many
Xsituations.
X.PP
X.PP
X.PP
X.bp
X.NH
XObserving
X.br
X.NH 2
XThe\ \fBobserve\fR\ Program
X.br
X.PP
XThis program is used to prepare for astronomical observations and for
Xephemeris calculation.  It can calculate the position of the major
Xplanets, the satellites of Jupiter and Saturn, and minor planets and
Xcomets given either orbital elements or a tabulated ephemeris.
XCoordinates of stationary objects may also be input.  It calculates
X(approximate) rise and set times, and transit times, of all objects to
Xbe observed.  It calculates the (approximate) altitude and azimuth of
Xobjects at sun rise and set, and morning and evening twilight.
X.PP
XThe information (coordinates, rise and set times) may be prepared for
Xeither a single time or a sequence of times.
X.PP
XOutput includes a file containing the timetable of events for the
Xevening or evenings.  The coordinates of the sun and moon, plus any
Xplanets, minor planets, and comets are placed in a readable text file,
Xwith other calculated values for solar system objects (e.g. distance to
Xearth).  The coordinates of all objects to be observed are placed in
Xfiles in formats to be read by the other programs in this family, namely
X\&\fBdataconv\fR and the starchart charting programs.  A file listing the
X(approximate) altitude and azimuth of objects at sun rise and set, and
Xmorning and evening twilight is output.  If satellite positions are to
Xbe computed, these coordinates are placed in one file, and a separate
XPostScript file graphically showing their positions relative to the
Xprimary is also produced.
X.PP
XThese output files are optional: any subset of the possible output files
Xmay be produced.
X.PP
XParameters set the location of the observer, control what objects are to
Xbe observed, and designate the time or times of interest.
X.PP
XCurrently, there are some limitations to the program:
X.IP
X.IP \(bu\
XMinor corrections such as parallax and nutation are not made.
X.IP
X.IP \(bu\
XPositions are accurate enough for most applications other than
Xoccultations.
X.IP
X.IP \(bu\
XRise and set times may be off by several minutes.
X.IP
X.IP \(bu\
XPositions of Saturn's satellites are approximate, good enough for
Xidentification of satellites.
X.PP
X.PP
X.PP
X.NH 2
XControls\ and\ Input\ for\ the\ \fBobserve\fR\ program
X.br
X.PP
XCommand line options set the location of the observer, control what
Xobjects are to be observed, control the output files produced, and
Xdesignate the time or times of interest.  The default location of the
Xobserver is set when the program is compiled.
X.PP
X.IP \f(CW\`-m\'\fR\
XMeridian of longitude, measured East of Greenwich.  The USA is West of
XGreenwich, and the longitude is negative for all USA locations.  One to
Xthree numbers can be used: degrees, degrees and minutes, or degrees
Xminutes and seconds.
X.IP
X.IP \f(CW\`-l\'\fR\
XLatitude.  One to three numbers can be used: degrees, degrees and
Xminutes, or degrees minutes and seconds.
X.IP
X.IP \f(CW\`-a\'\fR\
XAltitude in meters.
X.IP
X.IP \f(CW\`-z\'\fR\
XTime zone in hours East of Greenwich, again, this number is negative
Xfor USA locations.  This does not include any effects of daylight
Xsavings.
X.IP
X.IP \f(CW\`-d\'\fR\
XThe date or dates of observation in UT are specified with this flag.
XThe dates for the \f(CW\`-d\'\fR option are each specified as a string
Xconsisting of month, day, and optional year (use if different from the
Xcurrent year).  The month may be encoded as above, e.g. \f(CW\`Aug\'\fR for
Xaugust.  Using the first three letters of the English name for the month
Xalways works, as does the Roman numeral form.  Some other common
Xabbreviations also work.  The year may also be specified, the default is
Xthe current year.  The day may be fractional, e.g. 1.25 is 6 am UT on
Xthe first.  An optional third parameter is the increment of time to be
Xused in stepping between the two dates.
X.IP
X.IP \f(CW\`-o\'\fR\
XThis sets names used for the output files and controls which output
Xfiles are produced.  The output file names all have the form
X\&\f(CW\`\fIoutfile_root\fR.XXX\'\fR, where \fIoutfile_root\fR is set at
Xcompile time (usually to \f(CW\`planet\'\fR), or is set to the argument for
Xthis option. The \f(CW\`-o\'\fR may be followed with a letter or letters from
Xthe set "aeios" to select the altaz, eph, sif, obs, and star files,
Xrespectively.  e.g. \f(CW\`-oae austin\'\fR would produce only the output files
X"austin.altaz" and "austin.eph".
X.IP
X.IP \f(CW\`-p\'\fR\
XThe positions of any or all of the major planets at the time(s) may be
Xcalculated.  This is specified either as \f(CW\`-p\'\fR which causes the
Xpositions of all planets to be calculated, or individual planets may be
Xspecified by following the \f(CW\`-p\'\fR with a letter or letters from the
Xsequence "MVmJsUN".  The positions of the sun and moon are always
Xcalculated, since they always have some effect on observing conditions.
X.IP
X.IP \f(CW\`-s\'\fR\
XThe -s option causes the \f(CW\`.sat\'\fR and \f(CW\`.sat_PS\'\fR files to be
Xproduced for the satellites of Jupiter and Saturn.  \f(CW\`-s\'\fR implies
X\&\f(CW\`-p\'\fR.  With the \f(CW\`-si\'\fR option the drawings in the PS file are
Xflipped north to south (if for one time) or east to west (if for
Xmultiple times) to produce an inverted view.
X.IP
X.IP \f(CW\`-f\'\fR\
XInput object data is contained in files in several formats.  The
X\&\f(CW\`-f \fIfilename\fR \fIformat\fR\'\fR option sets this input file.
X.IP
X.IP \f(CW\`-n\'\fR\
XFor some input file formats, the name of the object must be specified
Xusing the \f(CW\`-n\'\fR option.
X.IP
X.PP
XSample data files should be used for the file formats used for input
Xfiles.  The format names are \f(CW\`obj\'\fR for fixed objects, \f(CW\`ell_e\'\fR
Xand \f(CW\`par_e\'\fR for parabolic orbital elements, and \f(CW\`emp\'\fR,
X\&\f(CW\`empb\'\fR, \f(CW\`aa\'\fR, \f(CW\`st\'\fR, and \f(CW\`iau\'\fR for tabulated
Xephemerides.  The fixed object format contains the coordinates, name,
Xmagnitude, type and size of objects to be observed.  The other file
Xformats are used for comets and minor planets, and are discussed below.
X.PP
X.PP
XThe output files are named \f(CW\`\fIoutfile_root\fR.XXX\'\fR where XXX is:
X.IP \f(CW\`altaz\'\fR\
Xaltitude and azimuth of objects at sun rise and set, and morning and
Xevening twilight.
X.IP
X.IP \f(CW\`eph\'\fR\
Xephemeris of sun, moon and objects specified.
X.IP
X.IP \f(CW\`obs\'\fR\
Xobservability of objects: rise and set times of objects, twilight times,
Xetc.
X.IP
X.IP \f(CW\`star\'\fR\
X\&\f(CW\`lineread\'\fR format file containing coordinates (equinox 2000) of the
Xobject(s), sun, moon.
X.IP
X.IP \f(CW\`sif\'\fR\
X\&\f(CW\`sif\'\fR format file containing the same information as the .star file.
XThe separation character is \f(CW\`;\'\fR.
X.IP
X.IP \f(CW\`sat\'\fR\
XLocations of the major satellites of Jupiter and Saturn with respect to
Xthe primary.
X.IP
X.IP \f(CW\`sat_PS\'\fR\
XPostScript file drawing either: one page showing appearance of Jupiter
Xand Saturn with satellites, and relative sizes and orientations of
XMercury, Venus, Mars, Jupiter, and Saturn, and the Moon; or several
Xpages showing Jupiter and Saturn with moons on a sequence of times if a
Xrange of dates was specified.
X.IP
X.PP
X.NH 2
XPlanetary\ Positions
X.br
X.PP
XPlanetary positions are calculated with moderate precision.  Formulae
Xare largely from \fIAstronomical Formulae for Calculators\fR by Jean
XMeesus.  Minor corrections are currently ignored.
X.PP
X.NH 2
XComets\ and\ Minor\ Planets
X.br
X.PP
XComets and minor planet positions may be calculated either directly from
Xthe orbital elements or by interpolating a tabulated ephemeris.  The
Xcalculation from orbital elements is most convenient, but the tabulated
Xephemeris is likely to be slightly more accurate.
X.PP
X.PP
X.NH 3
XOrbits
X.br
X.PP
XThe coordinates of objects in elliptical or parabolic orbits may be
Xcalculated from orbital elements given in files of format \f(CW\`ell_e\'\fR
Xand \f(CW\`par_e\'\fR respectively.
X.PP
XOrbital elements are:
X.IP \f(CW\`a\'\fR\
Xsemimajor axis, A.U.
X.IP
X.IP \f(CW\`q\'\fR\
Xperihelion distance, A.U.
X.IP
X.IP \f(CW\`e\'\fR\
Xeccentricity
X.IP
X.IP \f(CW\`i\'\fR\
Xinclination (degrees)
X.IP
X.IP \f(CW\`omega\'\fR\
Xargument of perihelion
X.IP
X.IP \f(CW\`Omega\'\fR\
Xlongitude of ascending node
X.IP
X.IP \f(CW\`n\'\fR\
Xmean motion (degrees/day)
X.IP
X.IP \f(CW\`M\'\fR\
XMean anomaly at epoch
X.IP
X.IP \f(CW\`T\'\fR\
XTime of perihelion.
X.IP
X.PP
XFor elliptical orbits, \f(CW\`q\'\fR and \f(CW\`T\'\fR are not needed; for
Xparabolic orbits, only \f(CW\`q\'\fR, \f(CW\`i\'\fR, \f(CW\`omega\'\fR and \f(CW\`Omega\'\fR
Xare needed.
X.PP
X.PP
XOrbital elements are referred to a certain equinox, and apply on a
Xcertain epoch date.
X.PP
XIf \f(CW\`a\'\fR is not given, it may be calculated from \f(CW\`a\'\fR =
X\&\f(CW\`q\'\fR/(1-\f(CW\`e\'\fR).
X.PP
XIf \f(CW\`n\'\fR is not given, it may be calculated from \f(CW\`n\'\fR =
X0.985609/(\f(CW\`a\'\fR*sqrt(\f(CW\`a\'\fR)).
X.PP
XIf \f(CW\`M\'\fR is not given, use \f(CW\`M\'\fR = (\f(CW\`Epoch_date\'\fR - \f(CW\`T\'\fR)
X* \f(CW\`n\'\fR.
X.PP
XThe magnitude of an asteroid may be calculated from two parameters:
X\&\f(CW\`G\'\fR and \f(CW\`H\'\fR.  The magnitude of a comet may be calculated from
Xthe parameters \f(CW\`g\'\fR and \f(CW\`kappa\'\fR.
X.PP
X.NH 3
XInterpolation\ of\ Ephemerides
X.br
X.PP
XAll ephemeris formats have date, RA, DEC, then other info.  Date is the
Xmonth in characters, then the day of the month.  How the month is
Xencoded is format dependent, examples include \f(CW\`IX\'\fR \f(CW\`Sept.\'\fR
X\&\f(CW\`Sep\'\fR \f(CW\`Sep.\'\fR \f(CW\`September\'\fR.  Year is current year unless
Xspecified in command line, and is the year of the first date.  Dates
Xmust be in increasing order: 3 followed by 4, December followed by
XJanuary.
X.PP
XThe formats are:
X.IP \f(CW\`emp\'\fR\
XFormat used in the Russian \fIEphemerides of minor planets\fR.
X.IP
X.IP \f(CW\`empb\'\fR\
XFormat used in the Russian \fIEphemerides of minor planets\fR for
Xbright and unusual asteroids.
X.IP
X.IP \f(CW\`aa\'\fR\
XFormat used by the \fIAstronomical Almanac\fR.
X.IP
X.IP \f(CW\`st\'\fR\
XFormat commonly used by \fISky and Telescope\fR magazine.
X.IP
X.IP \f(CW\`iau\'\fR\
XFormat commonly used by IAU Circulars.
X.PP
X.NH 2
XTime\ Line\ of\ Events
X.br
X.PP
XThe \f(CW\`.obs\'\fR file contains a timeline of events for the night or nights
Xof observation.  Events include sun and moon rise and set, morning and
Xevening twilight, and for each object to be observed: the rise and set
Xtimes,  the times when they are 20 degrees and 30 degrees above the
Xhorizon, and the time of their transit (when they cross the line from
Xnorth to south passing directly overhead, and are at their maximum
Xaltitude above the horizon).
X.PP
XThe times, especially sun and moon rise and set are approximate.
X.PP
XThe timeline should help you plan your evening, so you know when to
Xbegin and end (twilight), and when the moon will interfere.  It helps
Xyou plan to observe the objects when they are well placed, and ensure
Xthat you can observe an object before it has fallen too low in the sky.
X.PP
X.NH 2
XSatellites\ of\ Jupiter\ and\ Saturn
X.br
X.PP
XThe positions of the major satellites of Jupiter and Saturn are
Xcalculated for the time or times of interest.  The Saturn satellite
Xpositions in particular are approximate, but are certainly good enough
Xfor identification purposes.
X.PP
XThe positions are output in the \f(CW\`.sat\'\fR file, and also illustrated in
XPostScript in the \f(CW\`.sat_PS\'\fR file.
X.PP
XIf more than one time is specified, the PostScript program draws many
XJupiters and Saturns with their moons on a page (with separate pages for
XJupiter and Saturn).  If one time is specified, a single page is
Xproduced containing large drawings of Jupiter and Saturn with their
Xmoons.  As a bonus, this single page also illustrates the phases and
Xorientations of Mercury, Venus, Mars, Jupiter and Saturn (with rings),
Xand the moon.
X.PP
X.bp
X.NH
XCharts
X.br
X.NH 2
XThe\ Starchart\ Programs\
X.br
X.PP
XThe starchart programs are variations of a single program, producing
Xoutput for different output devices.  All the programs produce
Xastronomical star charts from available databases.
X.PP
X.PP
X.PP
X.NH 2
XPurpose\ of\ Starchart
X.br
X.PP
XThe starchart programs have many potential uses: in education, preparing
Xillustrations, becoming familiar with the constellations and the sky;
Xbut it is primarily useful for preparing for observing.  It can prepare
Xlarge scale maps, finder charts, variable star charts, and illustrations
Xfor inclusion in an observing notebook.
X.PP
XA variety of map projections are available for various needs.
X.PP
X.NH 2
XFeatures
X.br
X.PP
XThere are many many features of potential use.  The programs can:
X.IP
X.IP \(bu\
XAllow for the creation of star charts of medium quality, comparable to
Xpublished works in data content.
X.IP
X.IP \(bu\
XAllow for the creation of custom star charts for use as finder maps for
Xspecific objects, including the labeling of stars with their magnitudes.
XInverted maps may also be produced.
X.IP
X.IP \(bu\
XAllow for the creation of figures of the sky overhead at any location
Xand time, as in the Sky and Telescope centerfold, or planispheres.
X.IP
X.IP \(bu\
XOptionally include in the above: planets (including the sun, moon,
Xasteroids, comets), fixed stars, nebulae, clusters, etc., lines for
Xconstellation shapes, constellation boundaries, paths of planets, the
Xecliptic, galactic equator, milky way isophots, etc.
X.IP
X.IP \(bu\
XUse color for objects, and stars by spectral type, when available for
Xthe given device.
X.IP
X.IP \(bu\
XLabel stars with their name, number or letter, and/or magnitude.
X.IP
X.IP \(bu\
XLabel other objects by name.
X.IP
X.IP \(bu\
XAllow custom star databases to be used to produce maps of the sky in,
Xfor example, 10,000 B.C.
X.IP
X.IP \(bu\
XInteract on the display to allow for interactive sky exploration, if the
Xdevice supports such interaction.
X.PP
XStarchart is intended to produce useful displays on any available
Xdevice, and to produce best results on high quality graphics printers,
Xespecially those using PostScript.  Output may be captured in files to
Xbe edited for especially customized maps.  Comments are included in the
Xoutput whenever possible to facilitate this editing.  Given a good
Xobject-oriented editor, professional quality maps may be easily
Xproduced.
X.PP
XThe program has a set of core routines for user interface and data
Xinput, while a set of specialized driver routines is provided for each
Xoutput device.
X.PP
X.NH 2
XNon-\ and\ Mis-\ Features
X.br
X.PP
XThere are some limitations remaining.
X.PP
XThe output is limited by the capabilities of the device.  However, even
Xthe best of the drivers has the following problems: it cannot detect and
Xavoid overlapping labels and stars, and it cannot allow the user to
Xinteract with the display and move the labels.  These limitations are
Xwhat distinguish the output from these programs from a professionally
Xprepared map.
X.PP
XThe current programs do not have user configurable Legend areas.
X.PP
X.NH 2
XObjects\ Drawn
X.br
X.PP
XThe objects drawn currently include:
X.PP
X.IP \f(CW\`Stars\'\fR\
XSize represents the magnitude.  For most devices, this is done by
Xrounding to the nearest integer magnitude, and drawing the star based on
Xthis; however, some versions, e.g. \fBstarpost\fR for PostScript, allow
Xfor continuous scaling of the size.  Color is determined from the star's
Xspectral class.
X.IP
X.IP \f(CW\`Planets\'\fR\
XOn some devices, separate symbols are drawn for each planet, on others
Xthey are all represented by the same symbol.  Major planets should be
Xdistinguished from comets and asteroids.  Color may be assigned in the
Xdatabase file.
X.IP
X.IP \f(CW\`Nebulae\'\fR\
XDiffuse, planetary and unspecified nebulae may be
Xdistinguished.  If the device can support it, size may represent the
Xdiameter of the nebulae (if provided in the database).  Color may be
Xassigned in the database file.
X.IP
X.IP \f(CW\`Galaxies\'\fR\
XSpiral, elliptical and unspecified galaxies may be
Xdistinguished.  If the device can support it, size may represent the
Xdiameter of the galaxy (if provided in the database).  Color may be
Xassigned in the database file.
X.IP
X.IP \f(CW\`Clusters\'\fR\
XOpen, globular and unspecified clusters may be
Xdistinguished.  If the device can support it, size may represent the
Xdiameter of the cluster (if provided in the database).  Color may be
Xassigned in the database file.
X.IP
X.IP \f(CW\`Other\'\fR\
XOther identified objects.  If the device can support it,
Xsize may represent the diameter of the object (if provided in the
Xdatabase).  Color may be assigned in the database file.
X.IP
X.IP \f(CW\`Unknown\'\fR\
XFor objects which haven't been identified.  If the
Xdevice can support it, size may represent the diameter of the object
X(if provided in the database).  Color may be assigned in the database
Xfile.
X.IP
X.IP \f(CW\`Vectors\'\fR\
XSolid, dashed, or dotted lines may be drawn using commands in a
Xdatabase.  Lines are drawn as projected segments of great circles, or by
Xlinear interpolation in latitude and longitude between endpoints.  Not
Xall line styles may be supported on some devices.  Color may be assigned
Xin the database file.
X.IP
X.IP \f(CW\`Text\'\fR\
XInvisible objects in a database are used to place text
Xlabels in the chart.
X.IP
X.IP \f(CW\`Comments\'\fR\
XLines for comments are allowed in database files.  They have no effect
Xon displayed output.
X.IP
X.IP \f(CW\`Filled\ areas\'\fR\
XImplemented as filled areas when possible for the device, otherwise as
Xoutlines.  Area boundaries may be segments of great circles or defined
Xby linear interpolation in latitude and longitude between endpoints.
X.PP
X.NH 2
XProjection\ Modes
X.br
X.PP
XThere are currently five projection modes available for a map.  The
Xdefault is Sanson's sinusoidal projection, which is area-preserving, but
Xfails near the poles.  This projection preserves both area and linearity
Xin Declination (y axis).  It gives good conformality (angle correctness)
Xnear the equator, so it is useful along the Ecliptic.  Lines of RA
Xconverge at the poles (unlike cylindrical projections), though
XCassiopeia and the Dipper reproduce well.
X.PP
XStereographic projection keeps circles circles, and can be used near the
Xpoles.
X.PP
XOrthographic projection is simple but very distorting; it is as if the
Xsphere of the sky were finite in size and viewed from infinity.
X.PP
XGnomonic projection projects great circles as straight lines, and is
Xtherefore very useful for charts to be used to plot meteor paths.  See
Xfor example the October 1988 \fISky and Telescope\fR.
X.PP
XRectangular projection is the simplest: latitude and longitude are
Xtranslated directly to x and y of the map.  Note that this is neither
Xcylindrical nor Mercator projection.
X.PP
XOnly the main map projection mode may be changed through the command
Xline and \f(CW\`.starrc\'\fR format control files; \f(CW\`mapwin\'\fR control may change
Xthe projection mode of the thumbnail map.
X.PP
X.NH 2
XThe\ Chart
X.br
X.PP
XA \fIchart\fR is a single page or display region.  Within that region are
Xone or more \fImap windows\fR, each of which may have an associated
X\&\fIlegend\fR region.  Each map window is independent of others.  Its
Xattributes are defined in a structure which contains its location and
Xsize, and parameters and flags used in determining what is placed in the
Xwindow.  The detailed appearance of each graphic element to be displayed
Xin the window is up to the driver.  The starchart main routines only
Xdefine the location of the element, and report which routine is calling
Xthe display function.  For each line in every star, planet, vector, or
Xother file, the main routines determine only \fIwhat\fR is to be
Xdrawn, and \fIwhere\fR on the entire device page it appears.  The
Xdevice specific drivers determine exactly how it appears on the
Xdevice.
X.PP
XThe page may have a title region, which is drawn once per page.  This
Xregion is entirely left to the driver.
X.PP
XThe initial values of map window structures are set in the device
Xdriver.  User input from the \f(CW\`.starrc\'\fR file and the command line may
Xchange these values, and then the driver has an opportunity to override
Xall settings, possibly through additional user input.  The structure may
Xbe read and written to \f(CW\`mapwin\'\fR files, which may be used for input to
Xdifferent drivers and (carefully) editted by the user.
X.PP
X.NH 3
XLayers
X.br
X.PP
XA map window consists of several \fIlayers\fR.  All layers are optional.
XThe order of layers is determined independently for each map window.
X.PP
XA map window has an \f(CW\`outline\'\fR, which is determined by the projection
Xmode.  For the Sanson's projection, RA and DEC tick axes are drawn.
X.PP
XA grid of arbitrary origin and spacing in RA and DEC may be drawn.
XThe RA and DEC lines are in two separate layers, called \f(CW\`ra_grid\'\fR
Xand \f(CW\`dec_grid\'\fR.
X.PP
XThe \f(CW\`ecliptic\'\fR is a separate layer.
X.PP
XA file defining constellation \f(CW\`boundaries\'\fR is provided, in
X\&\f(CW\`lineread\'\fR format.  The file contains vectors which are drawn in a
Xseparate layer.  Similarly, a \f(CW\`patterns\'\fR file contains figures
Xfor the constellations.  A third file and layer provides names for the
Xconstellations (\f(CW\`constlnames\'\fR).
X.PP
XFinally the set of files defined by the user is plotted.  These
Xcurrently include by default and in order a star file \f(CW\`yale.star\'\fR,
Xa file which is an index to files separated by region of sky called
X\&\f(CW\`index.indx\'\fR, a nebula database \f(CW\`neb.star\'\fR, and a planet
Xlocation file \f(CW\`planet.star\'\fR.  Additional files may be furnished by
Xthe user.
X.PP
XThe default is to treat these as one layer, \f(CW\`allfiles\'\fR, and draw
Xthe objects in each file in order.  Alternatively, for each map window,
Xthe order may be changed to draw all the symbols in all the files
Xfollowed by all the names in all the files, etc.  The supported elements
Xwhich are controlled by the data files are: glyph (symbol of object),
Xname (text to the right of object), magnitude label (text below and to
Xthe right of object), vectors, and filled areas.  These are layers
X\&\f(CW\`allfiles\'\fR, \f(CW\`allglyphs\'\fR, \f(CW\`allnames\'\fR, \f(CW\`allmaglbls\'\fR,
X\&\f(CW\`allvectors\'\fR, and \f(CW\`allareas\'\fR.
X.PP
XEach file has its own cutoff magnitudes for visibility of objects symbol
X(\fImaglim\fR) name label (\fIlbllim\fR) and Bayer/Flamsteed label
X(\fIgklim\fR).
X.PP
XFinally, a \f(CW\`legends\'\fR layer displays the legends area, if any, for a
Xwindow.
X.PP
XTo stress: any layer in any window may be skipped, and they may be drawn
Xin any order, independently.
X.PP
X.NH 2
XUser\ Controls
X.br
X.PP
XAs many chart controls as feasible may be set by various methods of
Xuser interaction.
X.PP
X.PP
X.NH 3
XCommand\ Line\ Controls
X.br
X.PP
END_OF_FILE
if test 33987 -ne `wc -c <'doc/as.ms.aa'`; then
    echo shar: \"'doc/as.ms.aa'\" unpacked with wrong size!
fi
# end of 'doc/as.ms.aa'
fi
echo shar: End of archive 24 \(of 32\).
cp /dev/null ark24isdone
MISSING=""
for I in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 ; do
    if test ! -f ark${I}isdone ; then
    MISSING="${MISSING} ${I}"
    fi
done
if test "${MISSING}" = "" ; then
    echo You have unpacked all 32 archives.
    rm -f ark[1-9]isdone ark[1-9][0-9]isdone
else
    echo You still need to unpack the following archives:
    echo "        " ${MISSING}
fi
##  End of shell archive.
exit 0