Astronomical Applications Department, U.S. Naval Observatory NOVASC Page 18
PRECESSION
short int precession (double tjd1, double *pos, double tjd2,
double *pos2)
PURPOSE:
Precesses equatorial rectangular coordinates from one epoch to
another. The coordinates are referred to the mean equator and
equinox of the two respective epochs.
INPUT
ARGUMENTS:
tjd1 (double)
TDB Julian date of first epoch.
pos[3] (double)
Position vector, geocentric equatorial rectangular coordinates,
referred to mean equator and equinox of first epoch.
tjd2 (double)
TDB Julian date of second epoch.
OUTPUT
ARGUMENTS:
pos2[3] (double)
Position vector, geocentric equatorial rectangular coordinates,
referred to mean equator and equinox of second epoch.
RETURNED
VALUE:
(short int)
0...Everything OK.
Discussion:
This function precesses a position vector
pos1
from the equatorial rectangular system of epoch
tjd1
to the equatorial rectangular system of epoch
tjd2
; the resulting vector is
pos2
. The two epochs are
completely arbitrary and the transformation is reversible. In typical usage, one of the two epochs will be
standard epoch J2000.0, that is, either
tjd1
or
tjd2
will be 2451545.0.
