Celestia is a space travel simulator. You can travel throughout the solar system, to any of over 100,000 stars, or even beyond the galaxy. There are add ins to expand the catalogs and images of comets, stars, solar system objects, and deep space objects. You can even add in fictional objects such as Star Wars, Star Trek, Babylon 5, etc.
Unlike most planetarium software, Celestia doesn’t confine you to the surface of the Earth. You can travel throughout the solar system, to any of over 100,000 stars, or even beyond the galaxy.
Runs as a stand-alone program on a user’s computer
Excellent space travel simulator. Additional stars, deep space, and solar system catalogs and images available as add in.
Open source freeware
Portable version available http://portableapps.com/apps/education/celestia_portable
Or – for even more fun take a look for yourself! …