The Standards of Fundamental Astronomy (SOFA) software libraries are a collection of subroutines that implement official International Astronomical Union (IAU) algorithms for astronomical computations. As of February 2009 they are available in both Fortran and C source code format. Capabilities The subroutines in the libraries cover the following areas: Calendars Time scales Earth's rotation and sidereal time Ephemerides (limited precision) Precession, nutation, polar motion Proper motion Star catalog conversions Astrometric transformations Galactic Coordinates Licensing As of the February 2009 release, SOFA licensing changed to allow use for any purpose, provided certain requirements are met. Previously, commercial usage was specifically excluded and required written agreement of the SOFA board. See also Naval Observatory Vector Astrometry Subroutines References External links SOFA Home Page Scholarpedia overview of SOFA International Astronomical Union and Working group "Standards of Fundamental Astronomy Celestial mechanics Astronomical coordinate systems Numerical software Astronomy software