slaAmp -

SYNOPSYS

PARAMETERS

double ra

double da

double date

double eq

double *rm

double *dm

DESCRIPTION

  Convert star RA,Dec from geocentric apparent to mean place.

  The mean coordinate system is the post IAU 1976 system,
  loosely called FK5.

Given

     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

Returned

     *rm      double      mean RA (radians)
     *dm      double      mean Dec (radians)

References

     1984 Astronomical Almanac, pp b39-b41.
     (also Lederle & Schwan, Astron. Astrophys. 134, 1-6, 1984)

Notes

     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.

Called

 slaMappa, slaAmpqk

  P.T.Wallace   Starlink   30 October 1993

SEE ALSO

• slalib.3