Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Part I of this series covered a simple Linux planetarium program, KStars.
But there are some questions KStars isn't very good at answering, like the question that began Part I: "What the heck are those really bright 'stars' in the sunset sky?" For viewing closeups of planets, monitoring the motion of the planets, getting precise predictions of events like eclipses, and other such information, you'll do better with a more powerful tool: XEphem.
XEphem is the oldest and arguably the best-known of the Linux planetarium programs. It's not included in most Linux distributions due to its license terms, but its source is available to download and the program is free for personal, educational or research use. You can buy it, too: $69.95 gets you a pre-compiled version of the program plus three CDs worth of extra data files that aren't in the free version. It's worth it if you're a sky junkie like I am.