astropy/astropy — pull request #645 by adrn (2013-01-16 22:37:17+00:00)
Title: Add a detailed example describing how to define custom coordinate system

I added a tutorial on how to define a custom coordinate system to the documentation. The example uses a coordinate system defined by the plane of orbit of the Sagittarius dwarf elliptical galaxy. Let me know if anything is unclear or if you spot any typos!