slaMappa -

SYNOPSYS

PARAMETERS

double eq

double date

double *amprms

DESCRIPTION

  Compute star-independent parameters in preparation for
  conversions between mean place and geocentric apparent place.

  The parameters produced by this routine are required in the
  parallax, light deflection, aberration, and precession/nutation
  parts of the mean/apparent transformations.

  The reference frames and timescales used are post IAU 1976.

Given

     eq       double      epoch of mean equinox to be used (Julian)
     date     double      TDB (JD-2400000.5)

Returned

       (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-v2) where v=modulus(abv)
       (12-20)  precession/nutation (3,3) matrix

References

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

Notes

  1)  For date, the distinction between the required TDB and TT
      is always negligible.  Moreover, for all but the most
      critical applications UTC is adequate.

  2)  The accuracy of the routines using the parameters amprms is
      limited by the routine slaEvp, used here to compute the
      Earth position and velocity by the methods of Stumpff.
      The maximum error in the resulting aberration corrections is
      about 0.3 milliarcsecond.

  3)  The vectors amprms(1-3) and amprms(4-6) are referred to
      the mean equinox and equator of epoch eq.

  4)  The parameters amprms produced by this routine are used by
      slaMapqk and slaMapqkz.

Called

     slaEpj, slaEvp, slaDvn, slaPrenut

  P.T.Wallace   Starlink   31 October 1993

SEE ALSO

• slalib.3