Celestia


Celestia is a 3D astronomy software program created by Chris Laurel. The program allows users to virtually travel through a computer generated universe. Celestia can display objects of various scales using OpenGL.
Celestia is available for AmigaOS 4, Linux, macOS, and Microsoft Windows, with beta versions for 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. In late 2016, the official Celestia forums were restored, and development restarted. As of 2020 beta testing builds of version 1.7.0 are available, as well as the bugfix release 1.6.2.
Celestia is available for download from free software websites. Between 2001 and May 2017, the former central distribution site SourceForge counted approximately 12 million downloads.

Functions

Celestia displays the Hipparcos Catalogue of 118,322 stars and a compiled catalogue of galaxies. Celestia uses the VSOP87 theory of planetary orbits to provide a solar and lunar eclipse finder and to display the orbital paths of 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, as well as the names and locations of Earth features.
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.
The user can change Celestia's field of view, and allows users to split the window into multiple panes. 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. The extension mechanism uses Lua as its built-in scripting language.

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 Celestia's ground, even when the Earth's oblateness is specified.
Many types of astronomical objects are not included with Celestia. Variable stars, supernovae, black holes, and nebulae are missing from the standard distribution. Some are available as add-ons.
Although objects that form part of a planetary system move, and stars rotate about their axes and orbit each other in multiple star systems, stellar proper motion is not simulated, and galaxies are at fixed locations. As a result, the constellations in Celestia do not gradually change shape as they do in the real world. In addition, Celestia's binary star catalogs only describe a few hundred systems of multiple stars. Most binary star systems cannot be simulated because adequate orbital information is not yet available.
Celestia does not include any stars that are more than a few thousand light-years from the Sun because the parallaxes of more distant stars are too small to be accurately measured by the Hipparcos astrometric satellite. In addition, objects in solar systems are only drawn to a distance of one light-year from their suns, and Celestia does not consider the wobbling of some stars induced by their planets.
Wavelength filtering is not implemented in Celestia's engine. The actual rendering tries to match human vision at the observer's position as accurately as possible. This means false-color maps and multi-color nebulae are not part of the official distribution. Camera artifacts such as lens flare and glare are not rendered.
Celestia also does not simulate gravity. For example, a near-Earth object approaching the Earth will not be deflected by the Earth's gravity unless the person who defined the NEO's trajectory for Celestia included that effect.
Some moons do not cast shadows on their planet during eclipses. This is because irregularly shaped objects do not cast shadows in the current version of Celestia, although this is planned for future versions.
Most real-world spacecraft such as Voyager 2 are not available in Celestia but are provided as add-ons by users.
Celestia uses the Julian calendar and cannot go back or forward more than 2 billion years, and the default time-setting system cannot go further than the years -9999 or 9999.

Add-ons

Well over 10 GB of extensions are available in addition to the base program, produced by an active user community.
Higher resolution surface textures are available for most solar system bodies, including Virtual Textures with coverage up to 32768 pixels wide, with selected coverage at higher resolutions. This allows closer views of the Earth, Mars, and the Moon. 3D models of historical and existing spacecraft are available flying in reasonably accurate trajectories, such as Sputnik 1, Voyager 2, the Hubble Space Telescope, and the International Space Station, as are extended data plots for stars, DSOs, as well as catalogs of asteroids and comets, and more than 96,000 locations on the Earth can be drawn by the program. Add-ons also include space objects such as red and blue supergiants, red and brown dwarfs, neutron stars, spinning pulsars, rotating black holes with accretion disks, protostars, star nursery nebulae, supernova remnants, planetary nebulae, galactic redshifts, geological planetary displays, planetary aurorae, rotating magnetic fields, animated solar prominences, 3D craters and mountains, and historic collision events.
Numerous scripts are available. These include simple tours, reconstructions of complex space missions such as Cassini–Huygens and Deep Impact, and scripts showing useful information, like size comparisons, or particular events such as multiple simultaneous eclipses of Jupiter's moons or the evolution of a star.
Fictional universes can be depicted, with planetary systems and 3D models—films such as , Star Trek and Star Wars, and TV shows including Stargate SG-1 and Babylon 5. Add-ons illustrating less well-known Web fiction, like Orion's Arm, or role-playing games, like 2300 AD, and personal works by members of the Celestia community depicting fictional solar systems with inhabited worlds, spacecraft, cities, and special effects can also be added.
Educational add-ons can also be implemented in different languages. These activities provide approximately 40 hours of space journeys and astronomical lessons to include extensive tours of the Celestia universe, the complete life cycle of stars, the solar system, the human space program, the Search for Extraterrestrial Intelligence, and depictions of astronomical events such as the formation of our moon billions of years ago, and the possible terraforming of Mars in the future.
In late 2017, a massive addon pack project called Celestia Origin was created, which replaces all vanilla textures and graphics with higher-quality renderings.

Uses in media

and ESA have used Celestia in their educational and outreach programs, as well as for interfacing to trajectory analysis software.
Celestia was used in the media by the CBS television show NCIS. Character Timothy McGee explains what Celestia is and how an add-on can allow the user to store a diary within the program, as well. Textures designed by Celestia graphic artists were used in the movie The Day After Tomorrow and the 2008 miniseries The Andromeda Strain. Celestia has also appeared on the Science Channel's Through the Wormhole. Eurogamer's Jim Rossignol named Celestia among a top 20 list of Summer of PC Freeware games in 2006.