Celestia

I did not know if you guys know about this program: I did a search, and did not find it too many times. It is an excellent space simulator. It can provide nice backgrounds for Blender space battles, etc.
Here is the link: http://www.shatters.net/celestia/
Here is a link to a similar program: http://www.openuniverse.org/

Another one is Universe Image Creator:
http://www.diardsoftware.com/

This one is shareware though.