Not every amateur uses—or wants to use—Windows or the Mac O/S. Many tech-savvy astronomers have turned to the "open source" operating system, Linux, for their computer needs, including the running of astronomy software. There are several planetarium packages available for this UNIX-like o/s, but the most fully realized is probably Elwood Downey's XEphem. Most open-source users are probably accustomed to software that's just a little different from what's offered to the Win-Mac masses, but even then this planetarium software (if it can be called that) may be something of a shock.
Executing XEphem does not bring up a computerized vista of the sky. Instead, the user is rewarded with a text-based main screen that displays current program status regarding time, location, and other settings, and which allows the user to change these settings, load catalog files, generate an ephemeris for various objects (that's where the "ephem" part of the program's name comes in), and access the program's graphical displays, the area of the program that is probably of the most interest to amateur astronomers.
Clicking "Skyview" under the main window's "View" menu brings up a very respectable graphical sky not unlike those provided by Megastar and Earth Centered Universe. This part of the program mostly works like what most of us are accustomed to, if with a few variations. For example, most planetariums handle zooms by having the user draw a box around the area of interest and click inside that box to execute the zoom. Not XEphem. A zoom is started by drawing a box, but it's finished by clicking a magnifying glass icon on the toolbar. That, like most of the program's other functions, worked well, but seems rather counterintuitive. XEphem can control go-to telescopes, but interfacing a scope is a decidedly more involved task than getting ASCOM talking. Since most Linux users are probably a lot more computer literate than average, that may not be a huge problem for them.
Why haven't we mentioned the program's object numbers? Because the installation package only includes relatively small "sample" catalogs; it's up to users to find and install catalogs that will bring the program up to the "millions of stars and hundreds of thousands of deep sky objects" of Windows and Macintosh programs, though it's fairly simple to do. Like many Linux offerings, XEphem sports a large and enthusiastic user community that can provide all the data files a deep sky happy CAT user could hope for.
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