This is a very quick discussion of a really cool Unix/Linux
astronomical program called Xephem. It's basically an ephemeris
program but it does much more such as creates multiple types of
astronomical charts and animated movies. It's modular as well,
allowing data from external sources to be imported. Xephem
differs from programs such as Kstars or Stellarium in that it is a
professional application while others are geared towards
You can make animated GIFs which is really cool. You can also add
professional catalogs of data and ephemeris elements. The "trail"
feature is cool, it lets you trace out the path of an object over
time. Below are two examples where I show the trails of Comets
Hayakutake and Hale-Bopp when they made their glorious appearance
during spring of 1996 and 1997.