KStars
Screenshot of KStars showing the night sky from Hanover.
KStars is a planetarium program that runs under GNU/Linux and other Unix like operating systems. It is part of KDE.
It provides an accurate graphical representation of the night sky, from any location on Earth, at any date and time. The display includes up to 126,000 stars, 13,000 deep sky objects, all 88 constellations, all 8 planets, the Sun and Moon, and thousands of comets and asteroids. It has features to appeal to users of all levels, from informative hypertext articles about astronomy, to robust control of telescopes and CCD cameras.