IAU Standards of Fundamental Astronomy (SOFA): Time & Date

Hohenkerk, Catherine

The International Astronomical Union’s (IAU) SOFA collection of ANSI C and Fortran software provides users with a library of routines that implement official IAU algorithms for fundamental astronomy computations. These include routines for Earth rotation, precession, nutation, polar motion, coordinate conversions, and astrometry, to list a few. These 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 Systems. Most of these routines 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, TCG as well as the well-known civil and Julian date conversions.

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