Are you interested in astronomy, the solar system, and space? Would you like to fly through the universe and observe our blue planet, the Moon, or the Milky Way from the outside? Then this free software application might be very interesting for you: Celestia is a 3D space simulator that runs on your Windows, Mac OS X, or Linux computer.
It contains almost 120,000 star positions collected by European Space Agency’s Hipparcos Space Astrometry Mission. It contains moons, asteroids, and even spacecraft, including their orbital paths, just to name a few. It can animate the constellations in real time as well as simulate object movements with much faster or slower velocity. Furthermore, additional information about these objects, craters, landing sites, observatories, etc. can also be displayed.
The software is open source, therefore many add-ons like high-detail textures for planets, satellites and their orbits, spacecraft, or animations are available. Anybody with programming skills can download the source code and further develop the software; even NASA and ESA use Celestia for creating animations, for Mars Express, for example.
So have a look at http://www.shatters.net/celestia, try out the software, and let us know what you think about it! And many thanks to the developers of this great simulator!