slaMap -

SYNOPSYS

PARAMETERS

double rm

double dm

double pr

double pd

double px

double rv

double eq

double date

double *ra

double *da

DESCRIPTION

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

  The reference frames and timescales used are post IAU 1976.

References

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

Given

     rm,dm    double     mean RA,Dec (rad)
     pr,pd    double     proper motions:  RA,Dec changes per Julian year
     px       double     parallax (arcsec)
     rv       double     radial velocity (km/sec, +ve if receding)
     eq       double     epoch and equinox of star data (Julian)
     date     double     TDB for apparent place (JD-2400000.5)

Returned

     *ra,*da  double     apparent RA,Dec (rad)

Called

     slaMappa       star-independent parameters
     slaMapqk       quick mean to apparent

Notes

     1)  eq is the Julian epoch specifying both the reference
         frame and the epoch of the position - usually 2000.
         For positions where the epoch and equinox are
         different, use the routine slaPm to apply proper
         motion corrections before using this routine.

     2)  The distinction between the required TDB and TDT is
         always negligible.  Moreover, for all but the most
         critical applications UTC is adequate.

     3)  The proper motions in RA are dRA/dt rather than
         cos(dec)*dra/dt.

     4)  This routine may be wasteful for some applications
         because it recomputes the Earth position/velocity and
         the precession/nutation matrix each time, and because
         it allows for parallax and proper motion.  Where
         multiple transformations are to be carried out for one
         epoch, a faster method is to call the slaMappa routine
         once and then either the slaMapqk routine (which includes
         parallax and proper motion) or slaMapqkz (which assumes
         zero parallax and proper motion).

  P.T.Wallace   Starlink   30 October 1993

SEE ALSO

• slalib.3