Convert star RA,Dec from geocentric apparent to mean place. The mean coordinate system is the post IAU 1976 system, loosely called FK5. Use of this routine is appropriate when efficiency is important and where many star positions are all to be transformed for one epoch and equinox. The star-independent parameters can be obtained by calling the slaMappa routine.
ra double apparent RA (radians) da double apparent Dec (radians)
(0) time interval for proper motion (Julian years) (1-3) barycentric position of the Earth (AU) (4-6) heliocentric direction of the Earth (unit vector) (7) (grav rad Sun)*2/(Sun-Earth distance) (8-10) abv: barycentric Earth velocity in units of c (11) sqrt(1-v*v) where v=modulus(abv) (12-20) precession/nutation (3,3) matrix
*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 accuracy is limited by the routine slaEvp, called by slaMappa, which computes the Earth position and velocity using the methods of Stumpff. The maximum error is about 0.3 milliarcsecond. 2) 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.
slaDcs2c, slaDimxv, slaDvdv, slaDvn, slaDcc2s, slaDranrm P.T.Wallace Starlink 31 October 1993