Planetarium Programs

by Sam Herchak

When I first started using planetarium programs on a home computer several years ago, I found them useful but at the same time, disappointing. Disappointing from an observing point of view because they just weren't accurate enough. Pluto's position was at least several arcminutes off and even with the Hubble Guide Star Catalog (HGSC) of 15 million stars/objects, you couldn't display the Trapezium in M42 correctly. But we all know what a difference a few years make in computing. Programming and databases have improved to the point that there is no reason your computer can't show Pluto and asteroid positions to within 1 arcsecond of their actual location and make starcharts as good as the Millennium Star Atlas! Without writing a book on what's available, I'll simply tell you my favorites.

For first-time buyers, "blow $40" and get SkyChart III by Tim DeBenedictis ( This program has Windows/Macintosh versions and even includes stellar data from the Hipparchus, Tycho, and Hubble catalogs for that low price! It has a beautiful display, good interface, great documentation (on disk), telescope control for many popular models, and its solar system accuracy will amaze you. Lunar/asteroidal occultations, Galilean "moon" events, and artificial satellites from standard two line elements (TLE's) are accurate to within one minute of the actual times I have observed. At this point, it doesn't have as many display/filtering options as I'd like, but those are in the works.

For experienced observers, Guide by Bill Gray ( is the best buy at $89 (and in my opinion, simply the best available). It is far easier to tell you what it can't do-CCD image processing is about it!

Otherwise, this program does it all. Besides unprecedented accuracy (a recently observed asteroidal occultation shows up as a 0.6 arcsecond "miss" with Guide), its displays are incredible. Instead of just showing the Milky Way area or the Veil Nebula as outlines, Guide has "isophotes" that show the relative intensities and gradients of the object. Instead of just showing the position of the Galilean moons around Jupiter, Guide shows their shadows on the planet (if appropriate). Instead of just a disk representing the Moon and planets, Guide has bitmap images. Zoom in on Mars and there is Syrtis Major (if actually visible from the observing location at the specified time). It's virtual observing!

The CD-ROM is packed with databases. When you "Get info" on an object (whether it be planet, asteroid, star, or galaxy), you'll get at least half a page of information. Guide displays the data from all the included catalogs because parts of one are often more accurate than parts of another. For deep sky objects, Herschel descriptions from the NGC2000 and the SAC Databases are included. You can also import/display information from RealSky and the new 500 million star A1.0/2.0 catalogs from the US Naval Observatory. The program allows precise astrometric measurements from CCD images and will even compute orbital elements from those measured positions.

The interface is highly configurable by the user, has a tremendous amount of supporting documentation (although some is hidden in obscure places), and will run on any PC including DOS machines. Although a Mac version is not in the works (possibly Linux though), I run it just fine on my Apple PowerPC computer with Windoze95 and the application Virtual-PC. The Sky, Megastar, Starry Nights, and Voyager II are all lacking compared to Guide in my opinion.

I highly recommend both companies. They have been a pleasure to deal with, providing prompt service and responses to my questions or suggestions. If only Christmas weren't so far away now....