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... (
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The program works with the following extensions:
cel,
clx and
celx
