Celestia

When you tire of looking at space, why not visit it?

Another beautiful piece of software. Celestia differentiates itself from planetarium software because it lets you travel through all of known space. You will want to see Saturn's rings (who doesn't?), but you can also travel far beyond our solar system.

It comes with a huge catalog of spacecraft, stars, planets, moons, asteroids and comets. You can also download extra libraries when your known space isn't quite big enough.

Everything is rendered in impressive 3D. Flying through space is a simple click and go.

http://www.shatters.net/celestia/