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.help evp Jun99 "Slalib Package"
.nf
SUBROUTINE slEVP (DATE, DEQX, DVB, DPB, DVH, DPH)
- - - -
E V P
- - - -
Barycentric and heliocentric velocity and position of the Earth
All arguments are double precision
Given:
DATE TDB (loosely ET) as a Modified Julian Date
(JD-2400000.5)
DEQX Julian Epoch (e.g. 2000.0D0) of mean equator and
equinox of the vectors returned. If DEQX .LE. 0D0,
all vectors are referred to the mean equator and
equinox (FK5) of epoch DATE.
Returned (all 3D Cartesian vectors):
DVB,DPB barycentric velocity, position
DVH,DPH heliocentric velocity, position
(Units are AU/s for velocity and AU for position)
Called: slEPJ, slPREC
Accuracy:
The maximum deviations from the JPL DE96 ephemeris are as
follows:
barycentric velocity 0.42 m/s
barycentric position 6900 km
heliocentric velocity 0.42 m/s
heliocentric position 1600 km
This routine is adapted from the BARVEL and BARCOR
subroutines of P.Stumpff, which are described in
Astron. Astrophys. Suppl. Ser. 41, 1-8 (1980). Most of the
changes are merely cosmetic and do not affect the results at
all. 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.
P.T.Wallace Starlink 21 March 1999
Copyright (C) 1999 Rutherford Appleton Laboratory
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
.fi
.endhelp
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