slaEvp -

SYNOPSYS

void slaEvp(date, deqx, dvb, dpb, dvh, dph)

PARAMETERS

double date
double deqx
double *dvb
double *dpb
double *dvh
double *dph

DESCRIPTION 


  Barycentric and heliocentric velocity and position of the Earth.

  All arguments are double precision.

Given


     date    double     TDB (loosely ET) as a Modified Julian Date
                                         (JD-2400000.5)

     deqx    double     Julian epoch (e.g. 2000.0) of mean equator and
                        equinox of the vectors returned.  If deqx <= 0.0,
                        all vectors are referred to the mean equator and
                        equinox (FK5) of epoch date.

Returned (all 3D Cartesian vectors)


     dvb,dpb double[3]  barycentric velocity, position

     dvh,dph double[3]  heliocentric velocity, position

  (Units are AU/s for velocity and AU for position)

Called 

 slaEpj, slaPrec

Accuracy


     The maximum deviations from the JPL DE96 ephemeris are as
follows 

     barycentric velocity                  42  cm/s
     barycentric position           0.000 046  AU

     heliocentric velocity                 42  cm/s
     heliocentric position          0.000 011  AU

  This routine is adapted from the BARVEL and BARCOR Fortran
  subroutines of P.Stumpff, which are described in
  Astron. Astrophys. Suppl. Ser. 41, 1-8 (1980).  The present
  routine uses double precision throughout;  most of the other
  changes are essentially cosmetic and do not affect the
  results.  However, some adjustments have been made so as to
  give results that refer to the new (IAU 1976 "FK5") equinox
  and precession, although the differences these changes make
  relative to the results from Stumpff's original "FK4" version
  are smaller than the inherent accuracy of the algorithm.  One
  minor shortcoming in the original routines that has not been
  corrected is that better numerical accuracy could be achieved
  if the various polynomial evaluations were nested.  Note also
  that one of Stumpff's precession constants differs by 0.001 arcsec
  from the value given in the Explanatory Supplement to the A.E.

  Defined in slamac.h:  D2PI, DS2R

  P.T.Wallace   Starlink   22 December 1993

SEE ALSO