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Set your controls for the heart of the Sun

Perhaps the most impressive astronomy software on Linux for the impressionable layperson with a passing interest in science fiction and the stars is Celestia. Celestia is an interactive 3D application for astronomical visualisation, and is free software, licensed under the GPL. Unlike most planetarium software Celestia allows the user to travel across the universe, seeing objects as they would be seen from a spacecraft, and is the perfect way to forget your responsibilities in front of your computer as you set your controls for the heart of the sun.


Zoom Celestia - The Earth
Celestia boasts 18 gigabytes of add-ons, which can be downloaded from the Celestia Motherlode, a repository for various add-ons like textures, models or celestial objects, real and fictional objects in space. A default install of Celestia includes over 100,000 stars, and more than 10,000 galaxies, and is based on the Hipparcus Catalogue (HIP) from the European Space Agency. The Motherlode add-ons extend the scope of Celestia to over 10 millions stars, and include adventures in space from A Space Odyssey to Star Wars and Star Trek in all its guises, as well as more academic explorations through distant galaxies and nebulae.


Zoom Celestia - Add-on of Starship Enterprise leaving a space dock
Celestia gives absolute beginners the possibility of taking virtual flight across the galaxy, coming in close to satellites and space stations, asteroids and planets. The user can travel through space in real time, or move to warp speed, visiting galaxies, stars, nebulae, black holes, planets, dwarf planets, moons, asteroids, comets and spacecraft, or circle the earth tracing the lights of the cities below.

Celestia has been employed by NASA and the European Space Agency as an educational tool and is popular in schools as a means of demonstrating the geometry and nature of the solar system and the breadth of space. Celestia also offers a specialised Educational Activities CD set or DVD to give pre-programmed and documented tours of between one and four hours duration around the solar system and further.

Astronomy Domine

For the more serious astronomer, the most venerated and venerable of Linux astronomy packages is Elwood Downey's XEphem. Xephem is written in C, X11 and Motif, and was orginally written for UNIX. The first release was XEphem 2.5 in December 1993. The name is a concatenation of X and ephemera.


Zoom The XEphem user interface
XEphem describes itself as "a scientific-grade interactive astronomical ephemeris package", which is used in professional environments to "compute heliocentric, geocentric and topocentric information for all objects" in the night sky.

Sadly, XEphem is not available under a free software license, although the Linux or UNIX source code may be downloaded for educational or personal use at zero cost. XEphem is not straightforward to install on most Linux distributions, and lacks the dazzling graphics effects of other packages, but has the benefit that it will run on fairly modest hardware, and is more ambitious in its scope. As far back as 2001, XEphem was described as "the de facto standard for astronomy packages on UNIX" and "the standard by which all programs, commercial or not, are compared."

This may still be true, but as in many areas of academic computing, free and open source software is changing the rules and expectations. Sharing comes naturally in a discipline where so much remains still to be discovered. At the moment Linux is more likely to be used on high-end solutions, controlling large-scale telescopes or running landers or spacecraft, than by the amateur on his or her desktop, but as in other fields, this is likely to change very soon.

For other feature articles by Richard Hillesley, please see the archive.

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