Celestia

Celestia is a really nice tool that lets you explore the Universe as it provides real-time 3D visualization of space.

Celestia is impressively comprehensive as it is based on the Hipparcos Catalogue (the result of the European Space Agency's "astrometric" mission from November 1989 to March 1993) and therefore contains more than 100,000 stars. Even though it already contains a detailed model of the solar system and can be used to additionally explore tens of thousands of other galaxies, the tool still provides the possibility of adding more objects to its library (mainly by downloading add-ons).

Another great thing about Celestia is the exponential zoom feature. It makes traveling around the space very fast and smooth. Passing from a faraway galaxy cluster to the close by Moon or Mars will be done in an instant. This makes Celestia really enjoyable to use, especially since it also comes with handy exploration features like a star browser, a solar system browser, and a tour guide. Its navigation menu allows quickly jumping to a solar object regardless of its type and location.

Though feature-rich and comprehensive, Celestia is not hard to use. Its interface is simple, straightforward and intuitive, allowing even complete beginners to handle it with ease.

Simply put, Celestia is a great tool, both educational and entertaining. The fact that it’s also open source makes it even more appealing. I enjoyed using it and recommend it with all my heart.