Celestia

Celestia is an free software, 3D astronomy program for Microsoft Windows, Mac OS X, and GNU/Linux created by Chris Laurel, it is software licensing under the GNU General Public License.

The program, based on the Hipparcos Catalogue, allows user to display objects ranging in scale from satellite to entire galaxy in three dimensions using OpenGL. Unlike most planetarium software, the user is free to travel about the Universe. Over 10GB of add-on content is available to supplement the basic program as a result of the small, but productive community of users that supports the program.

NASA and European Space Agency have used Celestia, but it is not to be confused with Celestia 2000, ESA s own program.

= Limitations =

There are some limitations in Celestia s modelling:

The default setting for Celestia s Earth is a perfect spheroid, which means that low Earth orbit satellites are not modeled accurately. However, this setting can be adjusted.

*Many, if not most, binary stars are not yet properly simulated. *Only solar system objects move; stars and galaxies are stationary.

= External links =

[http://www.shatters.net/celestia/ Official website]

[http://www.celestiamotherlode.net/ Collection of add-ons] made by various people

[http://learn.arc.nasa.gov/planets/ Page on Celestia] hosted by NASA

[http://www.esa.int/esaCP/SEM4GC374OD_Ireland_1.html#subhead2 Instance of ESA using Celestia]