Stellarium

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.

The default location is Paris, France. Use the mouse or arrow keys to look around. Use the page up and page down keys to zoom in and out. Zooming on nebulas or planets is very interesting. J slows down or reverses speed, L increases time speed, and K makes time return to normal speed. You can also use the time control buttons in the lower right of the screen. Press the H key for help, ctrl-Q to exit.

For more complete information, visit the Stellarium Wiki.

Installation

On Ubuntu or Debian systems, enter (as root):

apt-get install stellarium

On Red Hat Fedora, enter (as root):

yum install stellarium

For Windows and Mac OS X, go to http://www.stellarium.org/ and download the appropriate binary file.

For Windows users, run the downloaded file "setup.exe" and follow the instructions.

Mac OSX users should download the dmg file, double click on it to open, the application is contained inside, drag the application to your Applications folder.

(Note: I have only personally tested the Ubuntu version.)