http://www.astropy.org/

The Astropy Project is a community effort to develop a single core package for Astronomy in Python and foster interoperability between Python astronomy packages.

Constants (astropy.constants)

http://docs.astropy.org/en/stable/constants/index.html

astropy.constants contains a number of physical constants useful in Astronomy. Constants are Quantity objects with additional meta-data describing their provenance and uncertainties.

Astronomical Coordinate Systems (astropy.coordinates)

http://docs.astropy.org/en/stable/coordinates/index.html

The coordinates package provides classes for representing a variety of celestial/spatial coordinates, as well as tools for converting between common coordinate systems in a uniform way.

Models and Fitting (astropy.modeling)

http://docs.astropy.org/en/stable/modeling/index.html#introduction

astropy.modeling provides a framework for representing models and performing model evaluation and fitting. It currently supports 1-D and 2-D models and fitting with parameter constraints.