View source for Celestia

{{Short description|Astronomy computer program}}{{Distinguish|Celesta|Celestica}}
{{other uses|Celestia (disambiguation)|Celestial (disambiguation)}}
{{Refimprove|date=April 2011}}
{{Infobox software
| name = Celestia
| logo = Celestia.png
| screenshot = Jupiter, Io, and Europa.png
| caption = [[Europa (moon)|Europa]], [[Io (moon)|Io]], and [[Jupiter]] in Celestia
| author = Chris Laurel
| developer = Celestia Development Team
| released = {{Start date and age|2001|02|26|df=yes}}<ref>{{cite web|url=https://github.com/CelestiaProject/Celestia/releases/tag/arelease|title=Alpha release|website=[[GitHub]]|access-date=22 February 2020}}</ref>
| latest release version = 1.6.4
| latest release date = {{Start date and age|2023|11|05|df=yes}}<ref>{{cite web|url=https://github.com/CelestiaProject/Celestia/releases/tag/1.6.4|title=Release 1.6.4|website=[[GitHub]]|access-date=21 December 2023}}</ref>
| repo = <!-- This is provided by Wikidata -->
| programming language = [[C++]]
| operating system = [[AmigaOS 4]], [[BSD]], [[Linux]], [[macOS]], [[Microsoft Windows]], [[iOS]], [[Android (operating system)|Android]], [[FreeBSD]]
| size = '''Linux:'''    27.7 MB<br /><!--
                         -->'''AmigaOS 4:''' 44.4 MB<br /><!--
                         -->'''macOS:'''     38.7 MB<br /><!--
                         -->'''Windows:'''   32.8 MB<br /><!--
                         -->'''FreeBSD:'''   65.7 MB<br /><!--
                         -->'''Source code:''' 52.6 MB<!--
                         --><ref name="celestia-sourceforge" />
| language count = 31
| language footnote = <ref name=transifex>{{cite web|url=https://www.transifex.com/celestia/celestia/|title=Celestia localization|website=[[Transifex]]|access-date=22 February 2020|archive-date=22 February 2020|archive-url=https://web.archive.org/web/20200222185545/https://www.transifex.com/celestia/celestia/|url-status=dead}}</ref><ref group=note>Although it is available, most languages are still a work in progress.</ref>
| genre = [[Educational software]]
| license = [[GNU General Public License|GPLv2]]
| website = {{URL|https://celestiaproject.space/}}
}}

'''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 (software)|Stellarium]]. Celestia can display objects of various scales using [[OpenGL]].<ref group=note>There are three graphical front-ends available: [[OpenGL Utility Toolkit|GLUT]], [[GTK+]] or [[Qt (software)|Qt]].</ref>

Celestia is available for [[AmigaOS 4]],<ref>{{Cite web|date=2011-12-08|title=Celestia|url=https://www.amigaos.net/software/104/celestia|access-date=2021-09-13|website=AmigaOS|language=en}}</ref><ref>{{Cite web|title=OS4Depot - Your one stop for AmigaOS4 files|url=http://os4depot.net/?function=showfile&file=utility/scientific/celestia.lha|access-date=2021-09-13|website=os4depot.net}}</ref><ref>{{Cite web|title=Celestia ported to AmigaOS4.1 - Celestia Users - Celestia Forums|url=https://celestiaproject.space/forum/viewtopic.php?f=2&t=13018|access-date=2021-09-13|website=celestiaproject.space}}</ref> [[Linux]], [[macOS]], [[Microsoft Windows]], [[Xbox]], [[iOS]],<ref name="ios">{{cite web |author=Markerz |date=20 February 2020 |title=Mobile Celestia for iOS - Celestia Forums |url=https://celestiaproject.space/forum/viewtopic.php?f=4&t=20191 |access-date=23 October 2020 |website=celestiaproject.space}}</ref> [[VisionOS]],<ref name=":0">{{Cite web |date=2025-01-31 |title=Celestia Vision |url=https://apps.apple.com/us/app/celestia-vision/id6476618172 |access-date=2025-02-20 |website=App Store |language=en-US}}</ref> and [[Android (operating system)|Android]].<ref name="android">{{cite web |author=Markerz |date=21 March 2020 |title=Mobile Celestia for Android - Celestia Forums |url=https://celestiaproject.space/forum/viewtopic.php?f=4&t=20241 |access-date=23 October 2020 |website=celestiaproject.space}}</ref> Celestia is also available on [[FreeBSD]] as both a binary package and a [[FreeBSD Ports|port]].<ref>{{Cite web|date=2002-05-18|title=celestia: Scriptable space flight simulator for X11|url=https://www.freshports.org/astro/celestia/|access-date=2025-07-04|website=FreshPorts|language=en}}</ref><ref>{{Cite web|date=2006-05-04|title=celestia-gtk: Scriptable space flight simulator for X11|url=https://www.freshports.org/astro/celestia-gtk/|access-date=2025-07-04|website=FreshPorts|language=en}}</ref> 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.<ref name="celestia-news">{{cite web |date=10 June 2011 |title=Celestia: News |url=https://celestiaproject.space/news.html |access-date=22 February 2020 |website=celestiaproject.space}}</ref> Since then, some of its development team went to work on celestia.Sci,<ref>{{cite web |title=celestia.Sci Development |url=http://forum.celestialmatters.org/viewforum.php?f=11&sid=629a28cba24d26eba11119cacab98ed5 |url-status=dead |archive-url=https://web.archive.org/web/20170224134251/http://forum.celestialmatters.org/viewforum.php?f=11&sid=629a28cba24d26eba11119cacab98ed5 |archive-date=24 February 2017 |access-date=1 August 2022 |website=Celestial Matters Forums}}</ref> 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<ref>{{Cite web|url=https://www.fifthstarlabs.com/|title=Fifth Star Labs|website=www.fifthstarlabs.com|accessdate=March 28, 2024}}</ref> shortly after Celestia's development stopped, and began working on a planetarium app called Sky Guide.<ref>{{Cite web|url=https://apps.apple.com/au/app/sky-guide/id576588894|title=Sky Guide|date=November 6, 2023|website=App Store|accessdate=March 28, 2024}}</ref> In late 2016, the official Celestia forums were restored,<ref>{{cite web |title=Welcome to restored Celestia Forums - Announcements - Celestia Forums |url=https://celestiaproject.space/forum/viewtopic.php?f=17&t=17406 |access-date=9 July 2017 |website=celestiaproject.space |language=en-gb}}</ref> and development restarted under a new development team.<ref name="celestia170">{{cite web |title=Celestia 1.7.0 Development Thread - Celestia Forums |url=https://celestiaproject.space/forum/viewtopic.php?f=4&t=18372 |access-date=22 February 2020 |website=celestiaproject.space}}</ref> As of 2018, beta testing builds of version 1.7.0 are available.<ref>{{cite web |title=Celestia 1.7.0 windows installer - Development - Celestia Forums |url=https://celestiaproject.space/forum/viewtopic.php?f=4&t=21805 |access-date=1 August 2022 |website=celestiaproject.space}}</ref><ref name=celestiagithub>{{cite web|url=https://github.com/CelestiaProject/Celestia|title=Celestia GitHub|website=github.com|access-date=2 August 2022}}</ref> Celestia was ported to mobile devices in 2020,<ref name="ios" /><ref name="android" /><ref name=celestiamobi>{{cite web|url=https://celestia.mobi|title=Celestia|website=celestia.mobi|access-date=1 August 2022}}</ref> and in 2024 the same developer ported it to the [[Apple Vision Pro]].<ref name=":0" />

Celestia is available for download from its main website, celestiaproject.space,<ref>{{Cite web|url=https://celestiaproject.space/download.html|title=Celestia: Download|website=celestiaproject.space|accessdate=March 28, 2024}}</ref> but it can be obtained from a multitude of [[free software]] websites as well. Between 2001 and May 2017, the former central distribution site [[SourceForge]] counted approximately 12 million downloads.<ref>{{cite web|url=https://sourceforge.net/projects/celestia/files/stats/timeline?dates=2000-05-21+to+2017-05-27|title=Download Statistics: All Files|date=27 May 2017|website=[[SourceForge]]|access-date=14 March 2020}}</ref>

==Functions==
[[File:Celestia DSOs.jpg|thumb|left|Typical [[Deep sky|DSO]] survey in Celestia]]

Celestia versions 1.6.4 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 (spacecraft)|Gaia]], increasing the star count to over 2 million.<ref>{{cite web|url=https://github.com/ajtribick/celestia-gaia-stardb|title=Gaia EDR3 for Celestia/celestia.Sci|author=Andrew Tribick|website=[[GitHub]]|access-date=26 October 2022}}</ref> Celestia uses the [[VSOP (planets)|VSOP87]] theory of planetary orbits to provide a [[solar eclipse|solar]] and [[lunar eclipse]] finder and to display the orbital paths of [[planet]]s (including [[extrasolar planet]]s), [[dwarf planet]]s, [[natural satellite|moon]]s, [[asteroid]]s, [[comet]]s, artificial [[satellite]]s, 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 correction|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 {{citation needed span|date=March 2020|date arithmetic overflows at the year 5,874,774.}}

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 [[High-definition video|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)|Lua programming language]], which can execute many different commands.

==Limitations==
[[File:TrES-4 Ab Celestia.png|thumb|TrES-4 Ab as depicted in Celestia 1.7.0|244x244px]]
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 [[Flattening|oblateness]] is specified, as Celestia does not simulate 3D surfaces.

Many types of astronomical objects are not included with Celestia. [[Variable star]]s, [[supernova]]e, [[black hole]]s, and [[nebula]]e are missing from the standard distribution. Many of these 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 [[Galaxy|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 with 100% accuracy because adequate orbital information is not yet available.

Celestia does not include any stars that are more than a few thousand [[light-year]]s from the Sun because the parallaxes of more distant stars are too small to be accurately measured by the [[Hipparcos]] [[Astrometry|astrometric]] satellite. However, with the addition of Gaia data in 1.7.0, stars as far away as the [[Galactic Center]] are included. In addition, objects in star systems are only drawn to a distance of one light-year from their parent stars, any further and they will simply not be rendered at all. Similarly, there is a render limit for stars at 10 million light-years in versions 1.6.3 and under, increased to 1 billion light-years in 1.7.0. Any stars beyond that limit are not rendered, and stars that are close to the 1.7.0 render limit experience floating point errors, meaning their position is inaccurate. Finally, Celestia does not consider the [[Doppler spectroscopy|wobbling]] of some stars induced by their planets, unless said wobbling is very noticeable.

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, but many are available as add-ons. Camera artifacts such as [[lens flare]] and [[Glare (vision)|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, or used an XYZV file.

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. Additionally, moons smaller than 0.5% of their parent objects' size do not cast shadows at all, as the original development team decided that they would be too small to be relevant. However, the new development team has considered removing this hard-coded limit.

Most real-world [[spacecraft]] such as ''[[Voyager 2]]'' are not available in Celestia but are provided as add-ons by users. Additionally, most of the spacecraft included with Celestia 1.6.3 use outdated or low-quality models, such as the stock Mir model which is very basic and barely detailed, and the stock ISS model which hasn't had an update since around 2007, meaning it is missing a lot of modules that have been added to the ISS since then. However, there are many add-ons that replace these models with higher-quality and more up-to-date ones. Fortunately, version 1.7.0 will include better models upon its final release.

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==
[[File:Red Giant Earth.jpg|thumb|left| Possible Earth 5 billion years from now when the Sun goes red giant|241x241px]][[File:Moon VT.png|thumb|The Moon close-up, with a 64K VT (Virtual Texture) applied|247x247px]][[File:NGC 4361.png|thumb|An example of a user-created add-on which adds the nebula [[NGC 4361]]|227x227px]]
Well over 80&nbsp;[[gigabyte|GB]] of extensions are available in addition to the base program, produced by an active user community.<ref>{{cite web |author=SevenSpheres |date=1 March 2020 |title=List of Celestia addons - Celestia Forums |url=https://celestiaproject.space/forum/viewtopic.php?f=23&t=20205 |access-date=23 October 2020 |website=celestiaproject.space}}</ref><ref>{{cite web|title=The Celestia Motherlode: Home|url=http://celestiamotherlode.net/|access-date=22 February 2020|website=celestiamotherlode.net}}</ref>

Higher resolution surface textures are available for most [[Solar System]] bodies, including Virtual Textures with coverage up to 65536 pixels wide (0.625&nbsp;km/pixel at the Earth's equator), with selected coverage at higher resolutions. This allows closer views of well-mapped objects that have high-resolution VTs available for download. 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 plot]]s for stars (2 million with correct spatial coordinates), [[Deep-sky object|DSO]]s (nebulae, galaxies, [[open cluster]]s, etc.), 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 other objects such as red and blue supergiants, red and brown dwarfs, neutron stars, spinning pulsars, rotating black holes with accretion disks, protostars, Wolf-Rayet stars, star nursery nebulae, supernova remnants, planetary nebulae, galactic redshifts, geological planetary displays (e.g. 3D interiors, topographic and [[bathymetry|bathymetric]] maps, [[paleogeography]]), [[Aurora (astronomy)|planetary aurorae]], rotating magnetic fields, animated [[solar prominence]]s, 3D craters and mountains, and historic collision events (Either spacecraft such as ''[[Deep Impact (spacecraft)|Deep Impact]]'' and [[Double Asteroid Redirection Test|DART]], or meteoric impacts such as the [[Chelyabinsk meteor]]).

Numerous scripts are available. These include simple tours, reconstructions of complex space missions such as ''[[Cassini–Huygens]]'' and ''[[Deep Impact (spacecraft)|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 universe]]s can be depicted, with planetary systems and 3D models—films such as ''[[2001: A Space Odyssey (film)|2001: A Space Odyssey]]'', ''[[Star Trek]]'' and ''[[Star Wars]]'', and TV shows including ''[[Stargate SG-1]]'' and ''[[Babylon 5]]''. Add-ons illustrating less well-known internet fiction, like ''[[Orion's Arm]]'', or [[role-playing games]], like [[2300 AD]], and personal works by members of the Celestia community depicting fictional [[planetary systems]] with inhabited worlds, spacecraft, cities, and special effects can also be added.

[[File:Anthonybrusso10fictionalsystem.png|thumb|left|alt=Two planets with rings, the left planet is brown, and the right is blue. The rings of both planets are yellow brown in color.|An example of a user-made fictional planetary system in Celestia|233x233px]]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 (SETI), and depictions of astronomical events such as the formation of the Moon billions of years ago, and the possible [[terraforming of Mars]] in the future.<ref>{{cite web|url=http://celestiamotherlode.net/catalog/educational.php|title=The Celestia Motherlode: Educational Activities|website=celestiamotherlode.net|access-date=22 February 2020}}</ref><ref group="note">Installation instructions for the add-ons are available on [[wikibooks:Celestia|the Wikibooks page]].</ref> 

In mid 2016, a large addon pack project called Celestia Origin was created, which replaces all vanilla textures and graphics with higher-quality renderings, adds more minor objects such as [[Trans-Neptunian object|TNOs]] and asteroids, while also adding more [[Exoplanet|extrasolar planets]] with custom textures, more nebulae with full 3D and accurate models, more stars and galaxies, more [[Star cluster|star clusters]], more spacecraft, and a ton of more enhancements.<ref>{{cite web |author=Art Blos |title=Project "Celestia Origin" - Celestia Forums |url=https://celestiaproject.space/forum/viewtopic.php?f=23&t=17804 |access-date=12 August 2020 |website=celestiaproject.space}}</ref><ref>{{cite web |title=Celestia Origin <nowiki>|</nowiki> VK |url=https://vk.com/celestiaorigin |website=[[VK (service)|VK.com]] |access-date=12 August 2020 |language=ru}}</ref> In 2019, Celestia Forum member FarGetaNik created an addon pack called Project Echoes, featuring higher-quality renderings that replace all vanilla textures.<ref>{{cite web |author=FarGetaNik |title=Project Echoes (Celestia Content Rework) - Release 0.1 - Celestia Forums |url=https://celestiaproject.space/forum/viewtopic.php?f=23&t=19970 |access-date=12 August 2020 |website=celestiaproject.space}}</ref> Celestia 1.7.0 appears to use Project Echoes as inspiration for its textures.

==Uses in media==
[[NASA]] and [[European Space Agency|ESA]] have used Celestia in their educational<ref>{{cite web|url=http://learn.arc.nasa.gov/planets/|title=Celestia Exploration Activity|year=2005|work=NASA Learning Technologies|publisher=[[National Aeronautics and Space Administration]]|archive-url=https://web.archive.org/web/20071023211946/http://learn.arc.nasa.gov/planets/|archive-date=2007-10-23|url-status=dead|access-date=2007-10-26}}</ref> and outreach programs,<ref>{{cite web|url=http://www.esa.int/esaCP/SEMOUD374OD_index_0.html|title=Mars Express orbit lowered|year=2003|work=Closing in on the Red Planet|publisher=[[European Space Agency]]|access-date=2007-10-26|quote=Upcoming Mars Express flight orbits until 7 January, getting closer to the Red Planet. Generated with Celestia software.}}</ref> as well as for interfacing to trajectory analysis software.<ref>{{cite web|url=http://trajectory.estec.esa.int/Astro/3rd-astro-workshop-presentations/Space%20Trajectory%20Analysis%20(STA).pdf|title=Space Trajectory Analysis (STA)|last=Schouten|first=G|publisher=[[Delft University of Technology]]|archive-url=https://web.archive.org/web/20071128195756/http://trajectory.estec.esa.int/Astro/3rd-astro-workshop-presentations/Space%20Trajectory%20Analysis%20%28STA%29.pdf|archive-date=2007-11-28|url-status=dead}}</ref> The [[CNES|French Space Agency (CNES)]] created a heavily modified version of Celestia in 2016, called VTS Timeloop, and it has since been used by multiple space agencies, including ESA and CNES themselves.<ref>{{Cite web |title=Timeloop |url=https://timeloop.fr/vts/ |access-date=2022-10-30 |language=en-US}}</ref>

Celestia was used in the media by the CBS television show ''[[NCIS (TV series)|NCIS]]'' (Season 4, Episode 22: "[[NCIS (season 4)|In the Dark]]"). 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 (TV 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.<ref>{{Cite news |last=Rossignol |first=Jim |date=2006-07-18 |title=Eurogamer's Summer of PC Plenty |language=en-gb |work=[[Eurogamer]] |url=http://www.eurogamer.net/articles/a_20bestfreegames |access-date=2023-01-06}}</ref>

==See also==
{{Portal|Free and open-source software|Astronomy}}
{{div col begin|colwidth=20em}}
*[[Gravity (software)]]
*[[OpenUniverse]]
*[[Orbiter (simulator)]]
*[[Planetarium software]]
*[[SpaceEngine]]
*[[Space flight simulation game]]
**[[List of space flight simulation games]]
*[[List of observatory software]]

{{div col end}}

==Notes==
{{reflist|group=note}}

==References==
{{Reflist|30em|refs=
<ref name="celestia-sourceforge">
{{Cite web
  |url = https://sourceforge.net/projects/celestia/files/
  |title = Celestia - Browse Files at SourceForge.net
  |work = [[SourceForge]]
  |publisher = Geeknet, Inc
  |access-date = 9 June 2011}}
</ref>
}}

==External links==
* {{Commonscatinline}}
* {{Wikibooksinline}}
* {{Official website}}
* [https://github.com/CelestiaProject/Celestia/ GitHub repository] Current binaries and source code
* [https://github.com/Anthony-B-Russo10/Celestia-Archive/ Celestia Archive Repository] Archive of Windows, macOS, and Linux binaries
* [https://celestiaproject.space/forum/ Official Forums]
* [http://www.esa.int/esaCP/SEM4GC374OD_Ireland_1.html#subhead2 Instance of ESA using Celestia]
* [https://celestia.mobi/ Celestia.Mobi main site]

{{GTK}}
{{Astronomy software}}

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