Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope. It is being used in planetarium projectors. Just set your coordinates and go. Features:

• default catalogue of over 600,000 stars
• extra catalogues with more than 210 million stars
• asterisms and illustrations of the constellations
• constellations for ten different cultures
• images of nebulae (full Messier catalogue)
• realistic Milky Way
• very realistic atmosphere, sunrise and sunset
• the planets and their satellites Free for Mac OS X 10.3 or higher, version is also available for Windows. Version 0.10.2 is based on the recent release of QT 4.5, which should fix startup problems which some users experienced with version 0.10.1. This change should also solve some Mac rendering bugs and speed up the GUI elements of the program.