Celestia is a free space simulation in which you can explore the (known) universe from any point.

Celestia has the main bodies in our solar system beautifully rendered in 3D with great looking textures. You can visit the moons of Jupiter or visit the International Space Station whilst looking down on the Earth.

Celestia comes with many stars, planets and other objects but there is the ability to add more via add-ons which can be found by visiting the links page on Celestia's main web page, so you can always keep it up to date as more discoveries are made.

Celestia is a great educational tool for those wanting to learn more about the universe.

Here is a nice video of the demo of Celestia.