Project of the Month, May 2006

Stellarium Logo

Project leaders:

Name: Fabien ChéreauFabien Chéreau
Age: 25
Occupation or experience: Research Enginer in the Observatory of Paris. I currently work on the ESA satellite “Gaia”.
Education: INSA Lyon, France, Computer Science department
Location: Paris, France

Key developers:

Name: Johan MeurisJohan Meuris

Name: Johannes GajdosikJohannes Gajdosik
Age: 36
Occupation: Software developer
Education: Ph.D. Mathematics
Location: Vienna, Austria

Name: Robert SpearmanRobert Spearman
Age: 32
Occupation: President, Digitalis Education Solutions, Inc.
Education: BA Economics
Location: Bremerton, Wash., USA

Quote about

Simply great, the number one for open source development. Thank you very much.

Why did you place the project on

Because it provides nearly everything we need and use everyday : CVS, download servers, forums, trackers, mailing lists, etc.

How has helped you?

It really helped us raise the quality of the management of the project. I don’t think Johan would have contacted the developers to offer his services without SourceForge really provides the channel for goodwill.

The number one benefit of using is:

The CVS and the download servers.

Description of project

Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars, or a telescope. It’s designed to be fun to use, even for those who don’t much about astronomy.

Trove info

  • Operating System: Linux, Mac OS X, Windows, and more.
  • Requires a 3D card with hardware OpenGL acceleration
  • License: GNU General Public License (GPL)
  • Programming language: C/C++

Why and how did you get started?

Fabien: During a summer at my parents’ place I found a star catalog online and started to code in C++ to see what I could do with OpenGL rendering on my old Voodoo2 3D card.

Robert: In 2002 I wanted to develop a relatively low-cost portable planetarium product with all the features of a modern planetarium. Existing products were low tech pinhole projectors with extremely limited capabilities. I needed planetarium software I could customize and enhance as needed for embedding into this product (the Digitarium Alpha). I couldn’t afford to develop my own software. Stellarium had the photorealism I was looking for, a straightforward interface, and was open source. Eventually I became one of the main developers.

Johan: I got involved in 2004 when it became clear the project was looking for free constellation drawings, and I was eager to do an interpretation of the mythologic figures from western astronomy. Nowadays I make myself useful by working on the Web site, thinking about the program, and adding graphical polish, because I’m not a coder.

Johannes: Since version 5.0 I was attracted by the beautiful images of the night sky. For a long time I waited for accurate planetary satellite positions, a better and bigger star catalogue (tycho2) and telescope control. When nothing of this came into version 7.1, I decided to start with the satellite positions on my own. Fabien was nice enough to include my patches in the CVS.

What is the software’s intended audience?

Everyone who looks up at the night sky with a sense of wonder. Many are people who just want to have fun with their computer. Amateur astronomers use it as a tool to prepare evening observations. Teachers and professional astronomers use it for education. Some professional planetariums use it with dome projection.

How many people do you believe are using your software?

We see significant peaks when new versions are released. Last March was the first time we broke 100,000 downloads per month. I’d guess we have more than 500,000 users, but that’s fewer than those who could benefit from it. It should really be in every school, given that it’s free, yet powerful, and simple to use.

What are a couple of notable examples of how people are using your software?

The Hawaiian Studies Center is using Stellarium for exploring ancient Hawaiian constellations. Astronomers from the Observatory of Paris use it to teach astronomy. Many educators are using Stellarium with digital planetarium projectors. Planetariums running stellarium can be found on Some people are building small domes themselves and projecting images via a spherical mirror, so they can have their own immersive planetarium. There is an artist in France who wants to use it in a multimedia device for a museum; it will be projected along with a video of the sea in foreground. I have even read about someone who wants to install it in an elevator.

What gave you an indication that your project was becoming successful?

When the statistics on SF started to rise, we knew things were going well. Now we get requests for interviews or software bundling with magazines. People tell me how they found this nifty piece of free planetarium software. And at some point I started to receive more email messages than I had time to reply to.

What has been your biggest surprise?

Fabien: When I discovered that many people were actually using stellarium for professional reasons. The project was always a hobby for me.

Johan: The effort people make purely because they’re interested in something. Lately, this has been the translation effort for Stellarium on Launchpad, and a fantastic user’s guide that doesn’t just explain the program, but many astronomic concepts as well.

Johannes: That Stellarium is becoming SourceForge POTM.

Robert: I’m surprised that so few educators have heard of Stellarium. Even worse is how many say they don’t even teach astronomy in their school. Help us get the word out!

What has been your biggest challenge?

Fabien: To compute things such as object position and sky luminosity in real time, enabling smooth moving in position and time.

Johannes: The spheric mirror projection/distortion for spheric-mirror-projection planetariums.

Robert: Coordinating large code changes when all developers are short on time. Supporting Windows.

Why do you think your project has been so well received?

It’s beautiful, powerful, simple, and useful. It’s accessible to a lot of people, and more so with every release. It’s extremely simple to use, yet you can do advanced things with it. It’s free of cost. A lot of “professional” software is more difficult to use, with useless functions for normal curious desktop users. Stellarium is more realistic, intuitive, and smooth. We’re spreading basic knowledge about the skies that should be available to everyone, and doing it in an attractive way.

Where do you see your project going?

I see important steps with every new release. With the current releases we more or less struck a good chord in terms of features and ease of use, and I hope we can keep up the balancing act. Adding new features would therefore mean increasing usability. The big new thing in version 0.8.0 is internationalization, because making the program available to people in their own languages is absolutely essential. The developers have removed a big hindrance to more widespread adoption.

What’s on your project wish list?

Fabien: To make it truly multilingual, I have been spending days trying to make it support gettext properly. It’s a nightmare to keep the code multiplatform with this, but it’s starting to work now!

Johan: I’d like to see other interpretations of the constellations, more complete “sky cultures,” as we call them. The western interpretations are well known, but a different take on the constellations, be it Chinese, Persian, or Polynesian, would offer new views on how people across the globe have looked at the stars. I can help contributors with the graphical representation.

More extensive access to some configuration options is something else I’d appreciate. A lot of interesting settings are kept in a text file, and editing that shouldn’t be necessary. Many users are put off by it, so a more complete GUI would be most welcome.

Specific features like satellite tracking, comets, X-ray vision, and printing would be very cool.

Johannes: Realistic Mars atmosphere rendering, foreign planet/satellite landscapes, beleivable rendering of small bright objects (mag[-4..-20]), antialiased and smooth lines, tycho2, faster computation, multithreading support, Neptunian satellite ephemeris, accurate planetrary rotation, light travel time, asteroids, multiple windows showing different magnifications, telescope control, multiple screen – even multiple computer – support for planetariums with multiple projectors.

Robert: More language translations. Add GUI access to most features. Improve realism with rings, shadows, and eclipses, now that we are enabling off-earth viewpoints. Comets.

What are you most proud of?

Fabien: That my project is used for children’s scientific education.

Johan: That the designs I made for Stellarium – in my spare time, and for no real gain other than getting familiar with the constellations myself – became the most widely distributed work I’ve ever done, thanks to an open source project. That’s really gratifying for a student.

If you could change something about the project, what would it be?

I’d like the GUI to be more flexible. The one we currently use is somewhat home-made and static. Unfortunately, I’ve been unable to find a good replacement so far. I’d like to set up some usability observations; ease of use is the most important aspect of any product.

How do you coordinate the project?

It’s free work, so we have no real constraints. Bugs wait until someone want to fix them. We need someone with time to manage bug reports and assign them out.

Do you work on the project full-time, or do you have another job?

We all have jobs, or in Johan’s case, classes.

If you work on the project part-time, how much time would you say you spend, per week, on it?

Robert: It varies from more than full-time to very little depending on priorities.

Fabien: On average 6-7 hours per week, with peaks when it’s raining. (In winter it’s always raining in Paris.)

Johan: As the project graphics grunt, I have the comfortable position in the team that requires the least time. A Web site rewrite, a new panorama, or a wiki installation is always done in short spurts. When I’m just spending time browsing the support requests or the forum, I’m down to about two hours or less a week.

What is your development environment like?

Fabien: I use my laptop with Ubuntu Linux, and I develop mainly with KDevelop.

Johan: I do most of the graphics work in a Windows environment with a Wacom drawing tablet, but recently I’ve taken up Inkscape on an Ubuntu partition as an SVG editor.


This month we will release Stellarium 0.8.0. It will include translation in more than 20 languages and many major improvements for planet computing and projection. It is also the beginning of a major code re-organisation.

How can others contribute?

We need developers to help fix bugs, improve the GUI, and help with Windows and Mac OS X portability and testing. We need graphic artists to create landscapes and nebula images. I’d love to see more users add their experiences, add-ons (landscapes, scripts, nebula images) and customizations to the Stellarium wiki. High on everyone’s wish list are landscapes from ancient sites like Stonehenge, Gizeh, and Mayan ruins. We need people to help document the program. We need translators for the program, for the Web site, and for the documentation. We also appreciate congratulations messages on the forum, although we don’t have time to reply to them all. Drop by the forum on SourceForge; we’re always checking up on it.

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