Convert star RA,Dec from geocentric apparent to mean place. The mean coordinate system is the post IAU 1976 system, loosely called FK5.
ra double apparent RA (radians) da double apparent Dec (radians) date double TDB for apparent place (JD-2400000.5) eq double equinox: Julian epoch of mean place
*rm double mean RA (radians) *dm double mean Dec (radians)
1984 Astronomical Almanac, pp b39-b41. (also Lederle & Schwan, Astron. Astrophys. 134, 1-6, 1984)
1) The distinction between the required TDB and the more accessible TT is always negligible. Moreover, for all but the most critical applications UTC is adequate. 2) The accuracy is limited by the routine slaEvp, called by slaMappa, which computes the Earth positions and velocities using the methods of Stumpff. The maximum error is about 0.3 milliarcsecond. 3) Iterative techniques are used for the aberration and light deflection corrections so that the routines slaAmp (or slaAmpqk) and slaMap (or slaMapqk) are accurate inverses; even at the edge of the Sun's disc the discrepancy is only about 1 nanoarcsecond. 4) Where multiple apparent places are to be converted to mean places, for a fixed date and equinox, it is more efficient to use the slaMappa routine to compute the required parameters once, followed by one call to slaAmpqk per star.
slaMappa, slaAmpqk P.T.Wallace Starlink 30 October 1993