Celestia is an incredible web. Above all, I recommend the program with the same name offered for downloading. It's a kind of "3d Google Space" in which you can take a look in real time, follow orbits, travel, look for objects... incredible. But Celestia offers much more. In the principal web you can get 3d hi-res images of all kind of objects related to astronomy,a nd you can also upload yours. Worths to take a look!