IAU standards of fundamental astronomy (SOFA): Time and date

Abstract

The International Astronomical Union’s (IAU) SOFA collection of ANSI C and Fortran software provides users with a library of routines that implement official International Astronomical Union (IAU) algorithms for fundamental astronomy computations. These include routines for Earth rotation, precession, nutation, polar motion, coordinate conversions, and astrometry, to list a few. The routines form the various parts of the transformation between the International Terrestrial Reference System (ITRS) and the Celestial Reference System, either the Geocentric (GCRS), Barycentric (BCRS), or the International (ICRS) Celestial Reference System. Most require input parameters that include an “instant”—a time and date in the appropriate time scale. This poster highlights the routines in the categories Time Scales and Calendars, which transform between the time scales UTC, UT1, TAI, TT, TDB, TCB, and TCG as well as provide civil and Julian date conversions.