Astronomy Software

Mike Swanson

The modern computer has changed the world of the professional astronomer. Intense calculations that took many hours to perform by hand are now completed in fractions of a second by a computer. Computer simulations are used routinely to bolster or discount theories of stellar and cosmic evolution. And naturally, observatory telescopes are generally controlled by computers.

The world of the amateur astronomer has also benefited from the widespread availability of cheap, powerful computers. Huge catalogs of objects that were unwieldy at best are now easily sorted and searched. Sky charts that took years to accurately plot are now effortless and instantly created on the humble home computer. Even the palmtop computer has gotten into the act, plotting stars and deep sky objects on its diminutive screen or producing moon phases and other ephemeris at a moments notice.

I categorize astronomy software into three types: planetarium, session planning, and specialized.

Planetarium Software
Planetarium software is the most generic category. Based on several databases of objects, mostly stars and deep sky objects, planetarium software is designed primarily to produce star charts on the computer screen. The charts are plotted based on a location (longitude and latitude or city) and just about any date and time you would like. Objects in the extensive databases are plotted precisely on the charts under the control of filters that determine what appears and what is hidden. Planetarium software is perhaps more useful in the field than printed star charts, if you have a suitable portable computer. The view on the computer screen can be made to match the view in any given eyepiece, binoculars or the naked eye. Printed star charts are limited by their static nature.

There are many good planetarium software available, but the three I find most useful for the computer are TheSky, Starry Night Pro and Cartes du Ciel. All are fine tools for the amateur astronomer and also all will interface with computerized telescopes to provide enhanced control of both the scope and the software. For palmtop computers TheSky Pocket Edition and Planetarium for Palm are great programs for maximum portability. Both provide support for computerized telescope control. For additional programs and the cost and web sites for these, refer to the Computer Software page of the Resources section of the Ryukyu Astronomy Club web site.

Session Planning Software
Session planning software emphasizes the ability to search extensive catalogs of objects and produce lists of potential objects for viewing. Most also provide sky charting capabilities but not generally with the feature set of planetarium software. This category of software helps you get organized before you step out for the night. My favorites in this category are NexStar Observer List (my own program), Deepsky 2002 and AstroPlanner. AstroPlanner is especially notable as it is the only planning software currently available for both Macintosh as Windows computers. All three of these interface with some models of computerized telescopes to allow you to direct your scope to one object after another on your list. You will also find that programs of this type have the strongest capabilities in recording and organizing your typewritten observation comments. See the Computer Software page of the Resources section of the Ryukyu Astronomy Club web site for links to these programs.

Specialized Software
Specialized astronomy software is the catchall category. One of my favorites is the Virtual Moon Atlas by Patrick Chevalley and Christian Legrand. Available free for download from, Virtual Moon Atlas allows you to easily identify hundreds of surface features on the Moon as it provides a very realistic view including the changing phases as the terminator creeps across the lunar surface. You are provided complete control of the image as you can pan and zoom to zero in on any area of the visible surface of the Moon. This program is not a simple image of the Moon, but rather a fully realistic simulation of the Moon as it actually appears during its ever-changing phases.

Another excellent free offering is the AstroByte Logging System by Ron Reuter. AstroByte Logging System allows you to easily record your observations of any of the thousands of objects in its extensive database. You can also display or print a wide variety of reports. Download at

One last example is Mars Previewer II - a free program that displays a detailed view of the surface of Mars for any given date and time. Using this software, you can easily identify the features viewed in the eyepiece. Mars Previewer doesn't seem to have a permanent home, so you might need to search a little for it, but at the time of this writing it was available for download at

For additional software, I keep my eye on advertisements and announcements in monthly magazines like Sky and Telescope and Astronomy.

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