ERFA (Essential Routines for Fundamental Astronomy) is a C library containing key algorithms for astronomy, and is based on the SOFA library published by the International Astronomical Union (IAU). ERFA is intended to replicate the functionality of SOFA (aside from possible bugfixes in ERFA that have not yet been included in SOFA), but is licensed under a three-clause BSD license to enable its compatibility with a wide range of open source licenses.
