Celestia is a real-time 3D astronomy software program that was created in 2001 by Chris Laurel. The program allows users to virtually travel through the universe and explore celestial objects that have been catalogued. Celestia also doubles as a planetarium, but the user is not restricted to the Earth's surface, like in other planetarium software such as Stellarium. Celestia can display objects of various scales using OpenGL.
Celestia is available for AmigaOS 4, Linux, macOS, Microsoft Windows, iOS, and Android. It is free and open source software released under the GNU General Public License.
Celestia's development stopped in 2013, with the final release in 2011. Since then, some of its development team went to work on celestia.Sci, a cosmological visualizer featuring more realistic rendering of galaxies and planets, gravitational lensing, and many other scientifically accurate enhancements, but there have been no updates on the progress of the program since 2020. The original creator of Celestia, Chris Laurel, created Fifth Star Labs shortly after Celestia's development stopped, and began working on an iOS-only planetarium app called Sky Guide. In late 2016, the official Celestia forums were restored, and development restarted under a new development team. As of 2018, beta testing builds of version 1.7.0 are available, as well as the bugfix releases 1.6.2 and 1.6.3, which were released in 2020 and 2023 respectively. Celestia was ported to mobile devices in 2020, and it continues to receive updates and experimental beta versions.
Celestia is available for download from its main website, celestiaproject.space, but it can be obtained from a large multitude of free software websites as well. Between 2001 and May 2017, the former central distribution site SourceForge counted approximately 12 million downloads.
Functions
Celestia versions 1.6.3 and under display the Hipparcos Catalogue (HIP) of 118,322 stars and a compiled catalogue of galaxies, while version 1.7.0 includes stars from the Tycho-2 Catalogue alongside the Hipparcos stars, with some data from Gaia, increasing the star count to over 2 million. Celestia uses the VSOP87 theory of planetary orbits to provide a solar and lunar eclipse finder and to display the orbital paths of planets (including extrasolar planets), dwarf planets, moons, asteroids, comets, artificial satellites, and spacecraft.
Using the installed catalogues, the names of celestial objects can be displayed, including artificial satellites. The names and locations of Earth features such as continents, mountains, seas, oceans, and cities can also be displayed. Surface features on other celestial objects such as craters, basins and canyons can be shown as well.
Celestia allows users to navigate at different speeds, and allow users to orbit stars, planets, moons, and other space objects, track space objects such as spacecraft, asteroids, and comets as they fly by, or travel to and/or fly through galaxies. Light time delay is an optional function.
The time simulated by Celestia can be set to any time 2 billion years forward or backward from the present, although planetary orbits are only accurate within a few thousand years of the present day, and
Celestia simulates the appearance of atmospheres on planets and moons, planetshine on orbiting satellites, and miscellaneous planetary details such as sunrise and sunset. Information about the objects that Celestia draws can also be displayed, such as temperature, distance from observer, radius, rotational period, luminosity, and more.
The user can change Celestia's field of view, and the window can be split into multiple different panes, meaning that several objects can be displayed on the screen at once. Screenshots and movies can be captured in classic or HD resolutions. Celestia's support for gamepads and joysticks is relatively limited.
Celestia can be extended with new objects, and has support for third-party, user-created add-ons available for installation, both fictional and realistic. Add-ons are commonly made up of plain text files, textures, and occasionally 3D models. Celestia also uses the custom CEL scripting language, and improved CELX scripts written in the Lua programming language, which can execute many different commands.
Limitations
The default setting for Celestia's Earth is a spheroid. The irregular surface of the Earth causes low Earth orbit satellites to appear to be in the wrong places in the sky when watched from the surface, even when the Earth's oblateness is specified, as Celestia does not simulate 3D surfaces.