Background

SOFA operates under the auspices of the International Astronomical Union (IAU) to provide algorithms and software for use in astronomical computing. The initiative is managed by an international panel, the SOFA Board, appointed through IAU Division A. The Board obtains the latest IAU-approved models and theories from the fundamental-astronomy community, implements them as computer code and checks them for accuracy. SOFA works closely with all the Commissions of the Division and with the International Earth Rotation and Reference Systems Service (IERS).

The SOFA Collection consists of two libraries of routines, one coded in Fortran 77 the other in ANSI C. There is a suite of vector/matrix routines and various utilities that underpin the astronomy algorithms, which include routines for the following:

• Astrometry
• Calendars
• Time Scales
• Ecliptic Coordinates
• Earth Rotation and Sidereal Time
• Ephemerides (medium precision)
• Fundamental Arguments
• Galactic Coordinates
• Geocentric/Geodetic Transformations
• Precession, Nutation and Polar Motion
• Star Catalog Conversion

The link for the current Fortran 77 and ANSI C software gives information on how to obtain it and instructions on its use. Also provided are two validation programs — one for each language. Guides with examples for many of the SOFA routines can be found in the various Cookbooks.

Access to the archive of all previous releases may be obtained from SOFA's software archive. A selection of reports and papers from the IAU SOFA initiative is also available.