If you think Starry Night Pro 5 is just too expensive, here is another killing application for you! Celestia 
This astronomy simulator is able to be runned on multiplatforms such as Windows, Mac OS X and Linux (X86). Therefore, it covers a big area!
It has over 100,000 objects in its database! It also has the ability to fasten the speed of time. The objects included are really great in quality. It’s very nice for those who just want the vision enjoyment.
Objects Included
Solar System, Eclipse Shadows,
Comet Tails, Galaxies,
Constellations, Nebulae
It also allows you to capture movies and images. It’s really useful for those who want to do astronomy presentation. 
It will be saved as a .avi file.
Pros: Free, clean interface, fast loading speed, ability to capture movies and images, hot-keys are well set.
Cons: The interface isn’t user-friendly, inability to zoom (at least I can’t locate where is it 
)
