Celestia

**Celestia** is a 3D astronomy program created by Chris Laurel. The program is based on the Hipparcos Catalogue (HIP) and 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 small spacecraft to entire galaxies in three dimensions using OpenGL, from perspectives which would not be possible from a classic planetarium or other ground-based display. Celestia's final update came in 2011, version 1.6.1. 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, and it has never been publicly released. Celestia is available for AmigaOS 4, BSD, HaikuOS, Linux, macOS, Windows, Android, and iOS. Celestia is free software released under the GNU General Public License. NASA, ESA, and the CNES have used Celestia in their educational and outreach programs, as well as for interfacing to trajectory analysis software. In late 2016, the official Celestia website and forums were restored (originally at celestiaproject.net, then at celestia.space, and now at celestiaproject.space), and a new development team began developing 1.7.0 and a few bug-fix releases for the 1.6.x series. Since then, Celestia has been ported to mobile devices and 1.7.0 has seen rapid development in recent times.

There are three graphical front-ends available: GLUT, GTK+ or Qt, though Qt is only available in the 1.7.0 version which is still under heavy development.

**Note: The developers of celestia.Sci, as well as the Celestial Matters forums which hosted threads on the development of this program, are now completely inaccessible and have been for a few years. The current situation with celestia.Sci is that it is most likely not completed and will never be completed. No code of the program has ever been shared by the developers, only a few screenshots.**

## Functions

Celestia displays the Hipparcos Catalogue (HIP) of 118,322 stars, and version 1.7.0 uses the Hipparcos and Tycho-2 catalogues, with some extra stars and more accurate data from Gaia. Celestia uses a combination of the VSOP87B and VSOP87E theories of planetary orbits, and some JPL ephemerides for certain objects . This makes it possible to provide a solar and lunar eclipse finder and to accurately display the orbital paths of planets (including extrasolar planets), dwarf planets, moons,asteroids, comets, artificial satellites, and spacecraft. The user can vary the number of stars that are visible on the screen and have them drawn in different styles, as well as increase or decrease their brightness, which is also possible to do with galaxies.

Using simple keyboard controls, Celestia users can travel/fly through the Celestia universe at any speed from 0.001 m/s to millions of light years per second. Viewpoints can be set to look forward, backward, or at any angle to the direction of travel. Controls 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 nebulae and irregular, elliptical, and spiral galaxies (over 10,000 galaxies included).

The time simulated by Celestia can be set at any point in the future or past, although planetary orbits are only accurate within a few thousand years of the present day, and date arithmetic overflows at the year 5,874,774.

The names and positions of multitudes of objects in space can be displayed, from galaxies, star clusters, nebula, constellations, and stars to planets, moons, asteroids, comets, and artificial satellites, as well as the names and locations of cities, craters, observatories, valleys, landing sites, continents, mountains, seas, and other surface features.

Celestia displays such features as detailed atmospheres on planets and moons, planet shine on orbiting satellites, sunsets and sunrises, moving clouds, planetary rings, eclipse and ring shadows, constellation lines, borders and illustrations, night-side lights (of cities), detailed surface textures, specular reflections off water and ice, nebula gases, and star flares.

Information about the objects that Celestia draws can also be displayed. The radius, distance, length of the sidereal day, and average blackbody temperature of the planets are shown, and the distance, luminosity relative to the sun, spectral class, surface temperature, and radius of stars are indicated (the radii of stars in Celestia are sometimes inaccurate, so some addons might help and I suggest that you don't use Celestia as a reference.)

The user can change Celestia's field of view from as wide as 120 degrees to a highly magnifying 3.4 seconds of arc, while dividing the window into multiple panes, in order to observe several objects at the same time and including light time delay (only in the 1.7.0 Qt frontend) if desired.

Celestia's support for gamepads and joysticks is relatively limited, employing many keyboard shortcuts instead.

Celestia can be extended with new objects, and there are thousands of third-party, user-created add-ons available for installation, both fictional and realistic. The extension mechanism uses Lua as its built-in scripting language, as well as an older, custom scripting language created specifically for Celestia. Educational lessons and computer lesson plans are available.

## Download

Newest Version: Celestia 1.6.3

Please select the appropriate Celestia 1.6.3 or 1.7.0 package for your computer from the list below.

* https://github.com/CelestiaProject/Celestia/releases/tag/1.6.3 (1.6.3, all operating systems)
* https://apps.apple.com/us/app/celestia-space-simulator/id1500434829 (1.5.27, based on 1.7.0 for desktop, macOS and iOS download)
* https://play.google.com/store/apps/details?id=space.celestia.mobilecelestia (1.5.27, based on 1.7.0 for desktop, Android and Chromebook download)
* https://celestiaproject.space/deb.html (1.7.0, Debian and Debian-based Linux distros download)
* https://celestiaproject.space/ubnt.html (1.7.0, Ubuntu and Ubuntu-based Linux distros download)
* https://celestiaproject.space/otherdistros.html (1.7.0, Other Linux distros download)
* The Windows package of Celestia is a self-extracting archive. Download it to your computer and then run it.
* The macOS packages for 1.6.3 and 1.7.0 are both zipped bundles, choose your version, then download it and unpack.

### Source Code

* https://github.com/CelestiaProject/Celestia
* Celestia is an open-source project. As such, its source code is provided and is freely modifiable and redistributable as per the GNU Public License. Building and installation instructions for all operating systems are provided in the INSTALL file.