Celestia's source code is freely available on GitHub. Only official Celestia developers can upload modified code to the GitHub server, but anyone can download the code and modify it for their own purposes. If you would like to contribute code to the project, please discuss it on the Celestia Web Forum in its Celestia Development Forum.

A sociological comment:

As with most software projects with established developer communities and protocols, a potential contributor to Celestia will have to undergo a form of apprenticeship. The program is large and complex and its underlying design philosophy has to be understood. It also takes a while to gain the trust of the people currently working on the program. By themselves, programming skills aren't enough. Too often individuals unfamiliar with the program or with the people involved have suggested significant changes and have become discouraged because their ideas weren't incorporated immediately. Don't let this happen to you. Read the forum. Read the developers mailing list. Participate in discussions. Contribute ideas. Try out things with the code on your own. Be patient. It'll take a while.

The following sections describe how to obtain the code and modify it for specific operating systems.