Celestia is a real-time visual space simulation astronomy program. It is a cross platform, open source software and released under the GNU General Public License. NASA and ESA have used Celestia in their educational and for interfacing to trajectory analysis software. It allows users to travel through an extensive universe, modeled after reality, at any speed, in any direction and at any time in history. Celestia displays and interacts with objects ranging in scale from artificial satellites to entire galaxies in three dimensions using OpenGL. It is a perfect software for astronomer, educator, student, and teacher for astronomy purpose.