Celestia/Development/MacOS platform

Install XCode Tools
If you've not already done so, install Xcode 10 from Apple.

GitHub
Before compiling Celestia, you must obtain the source code. The very latest source code is kept in Celestia's GitHub repository. You can get the source code by following these instructions:
 * 1) Open Terminal
 * 2) See if Git is installed on your system. Type "git" in the terminal (without the quotes.) If you get a "command not found" error message, you need to install Git. See this guide for information on installing Git on Mac OS X.
 * 3) Type, or paste in:
 * 4) Wait for a while, until the download is complete.
 * 5)   and follow instructions from https://github.com/CelestiaProject/Celestia/blob/master/INSTALL.md