We might not be ready to set foot on Mars (even if we can grow potatoes), but that doesn't mean you can't have an amazing time coasting through the vacuum of space. Celestia is a free simulator that lets you explore the furthest reaches of the Milky Way, without the perils of rapid decompression, starvation and extreme solar radiation. Always an advantage.
Celestia is a full 3D rendering of our galaxy, including planets, stars, satellites and other celestial bodies. There are even models of man-made structures like the International Space Station, which you can track as it orbits the Earth.
Ground control to Major Tom
Clicking on a celestial object will send the camera swinging, then propel you towards it. From there, you can rotate the star, planet, satellite or comet, see its orbit, and even adjust the date and time. Speeding up the clock and watching a solar eclipse cross the face of the Earth is particularly satisfying – particularly if you tap Alt+Enter for full-screen mode.
If you tire of planet-hopping, you can also learn about stars, planets and other objects by right-clicking them and selecting 'Info'. The amount of detail will vary greatly, depending on how close the body is to Earth, but can be fascinating.
Download here: Celestia