Convert star from
geocentric apparent to mean place (post IAU 1976).
CALL sla_AMP (RA, DA, DATE, EQ, RM, DM)
TDB for apparent place
equinox: Julian epoch of mean place
The distinction between the required TDB and TT is always negligible. Moreover,
for all but the most critical applications UTC is adequate.
Iterative techniques are used for the aberration and light deflection corrections so
that the routines sla_AMP (or sla_AMPQK) and sla_MAP (or sla_MAPQK) are
accurate inverses; even at the edge of the Sun’s disc the discrepancy is only about
Where multiple apparent places are to be converted to mean places, for a fixed
date and equinox, it is more efficient to use the sla_MAPPA routine to compute the
required parameters once, followed by one call to sla_AMPQK per star.
For EQ=2000D0, the
agreement with ICRS sub-mas, limited by the precession-nutation model (IAU 1976
precession, Shirai & Fukushima 2001 forced nutation and precession corrections).
The accuracy is further limited by the routine sla_EVP, called by sla_MAPPA,
which computes the Earth position and velocity using the methods of Stumpff. The
maximum error is about 0.3 milliarcsecond.