In response to Tazamin:

I love G.E. too, but as far as that "Celestia" program, for fun, try this:
Center Jupiter and follow it and speed time up to 10,000,000 times and zoom in or out 'til u see all of Jupiter's moons, it's really wild! If you zoom out 'til u see the solar system, everything's swirling around Jupiter - even the Sun.
Now if u center Sol (sun) and follow it, with time sped up, you can see all the comets and everything revolve. thnx!