SkyMap is a "planetarium" program for Microsoft Windows 3.1 or later on the
PC. It draws maps of the sky, as seen from anywhere on Earth, for any date
between 4000BC and 8000AD. Two different types of map can be drawn - a
"Horizon" map, showing a local view of the sky as seen by an observer, and
an "Area" map showing a detailed view of a small area of the sky on an
RA/Dec grid.

"OK - so what's the big deal", you're probably thinking. "There's lots of
programs around for drawing star maps". Well, that's true! What distinguishes
SkyMap from the rest is the fact that it's been written with ACCURACY as its
number one goal. All data is computed and displayed using the most accurate
methods available to the author. Planetary positions, for example, have a
mean error (when compared to the "astronomical almanac") of less than half a
second of arc - the apparent diameter of Jupiter is typically 40 arc seconds,
for comparison!

SkyMap displays the following information:

Stars - the 1990 machine-readable version of the SAO star catalog is the
source of star data. The evaluation version of SkyMap comes with 15,700
stars to magnitude 7. Registered users receive a much larger database of
88,000 stars to magnitude 8.5 or (optionally) the complete SAO catalog of
259,000 stars to magnitude 9.5-ish. Stars can be labelled with Bayer letter,
Flamsteed number, or "proper name" identifications, and complete catalog
information on any star on the map can be obtained by clicking on it. Star
positions are corrected for precession, proper motion, nutation, aberration,
and refraction.

Planets - the positions of the planets Mercury to Pluto, plus the Sun and
Moon are shown, with a mean error of <0.5". The Moon is drawn with the
correct phase and orientation in the sky. Clicking on any planet displays
extensive positional and physical information (position, distance, phase,
visual magnitude, light time, etc). Planetary positions are rigorously
reduced to apparent place for the topocentric position of the observer.

Comets - the program comes with a catalog of comets, to which the user can
add, edit and delete entries. Any number of comets from the catalog can
be selected for display on the map. Any type of cometary orbit - elliptical,
parabolic, or hyperbolic - is correctly computed.

Asteroids - the program has a catalog of asteroids, to which the user can
add, edit and delete entries. Any number of asteroids from the database can
be selected for display on the map.

Non-stellar objects - the complete Saguaro Astronomy Club (SAC) v6 database
of 10,700 deep sky objects, including galaxies, clusters, nebulae, etc.
You can select which objects are displayed (eg globular clusters brighter
than magnitude 10). Extensive information about any object can be displayed
simply by clicking on it with the mouse. The registered version of the program
displays Dreyer object descriptions, classification information, and
observing notes for each object.

Constellations - figures, names, and official IAU boundaries of all 88
constellations can be displayed.

Object tracks - the program can display the path of any moving object
(planet, asteroid, or comet) as a line on a map. Points along the line can
be labelled with date and magnitude.

Miscellaneous - grids of altitude/azimuth, RA/Dec, etc, can be overlaid on
any map.

Searching - SkyMap has extensive search facilities, allowing any object in
the databases to be easily located. You can search for objects using either
catalog numbers (eg "Barnard 33"), or popular name (eg "Horsehead Nebula").

Naturally, with all this information a map could get pretty crowded! You can
select exactly which information is displayed, and switch classes of object on
and off with the click of the mouse button. All this can be done through
either the menus, or the toolbar. You can zoom in on any map to a virtually
unlimited extent, scroll around it, etc.

Once you have a map exactly as you want it, you can print it on any printer
supported by Windows. Even though I say it myself, printed maps are VERY nice,
and compare favorably with a high quality star atlas such as the
"Uranometria 2000", for example.

As if all this wasn't enough, you can also display pictures with SkyMap.
The current version of the program can display pictures in either GIF,
Windows bitmap, or NASA PDS format. You can simply use the program as a
picture viewer by manually opening a file from the menu, or (more fun!) you
can link a picture to an object, and have it displayed when you click the
mouse on the object. You can currently do this with planets, comets,
asteroids and deep sky objects. Note that the program isn't supplied with
any pictures, but there are a lot around. Registered users can buy a
collection of pretty pictures as an optional extra. To display pictures you
really need a video card capable or displaying 256 or more colours at once -
the standard 16-colour VGA mode is fairly horrible for image display!

As with anything, you've got to make compromises and I have to admit that
SkyMap is not the fastest program in the world :-) To be honest, you really
do need a machine with a maths co-processor. It'll run without one, but
drawing a map will take a long time - typically 30 seconds. Drawing the same
map on a machine with a co-processor will take perhaps 5 seconds. The program's
been written on a 486/33, and performance is fine on that machine.

If you have a CompuServe account, you can get the latest evaluation version
of SkyMap from ASTROFORUM, in Library 7 (Astronomy Software), files
"SKYMPA.ZIP" and "SKYMPB.ZIP". If you have Internet access, it can be
obtained by anonymous FTP from "oak.oakland.edu", directory
"/SimTel/msdos/astrnomy", files "skymp21a.zip" and "skymp21b.zip". If you
have neither of these, I will be pleased to send you a copy - just send
5 or $10 to cover postage and packing to:

Chris Marriott
9 Severn Road
Culcheth
Cheshire WA3 5ED
U.K.

