Celestia is fantastic in its sheer scale. Not only can you explore the planets, their moons, comets and many famous asteroids flying around the Solar System, but you can also hop away to visit nearby stars and even galaxies. On a micro level you can examine famous satellites like the ISS or Hubble Space Telescope as they orbit the earth, or (if you find the right third-party addon) follow the Voyager or Cassini space probes. The movement of each planetary body is precisely calculated to represent real world figures, so even jumping thousands of years into the future or past will yield impressively accurate orbit predictions.
As if all of this stuff wasn’t enough, you can download a heap of mods and texture enhancements from the www.celestiamotherlode.net to make the program even more enjoyable. You can add nebulae and ships, new planets and even galaxies. A high resolution Mars download lets you zoom in and see details on the martian surface down to the kilometer, spotting individual craters and rocks. It really does feel like you’re exploring a distant, new world.
System Requirements: Pentium 1 Ghz, 256 MB RAM, Windows 95