Stellarium Astronomy Software

Stellarium is free GPL software which renders realistic skies in real time with openGL. It is available for Linux/Unix, Windows and MacOSX.
With Stellarium, you really see what you can see with your eyes, binoculars or a small telescope.
Stellarium is also used in planetariums.

Discovered this Open Source program. It's available for Linux, Windows and MacOS X. Check out the other screenshots at the website to see what I mean.