/*
*+
* Name:
* palFk54z
* Purpose:
* Convert a J2000.0 FK5 star position to B1950.0 FK4 assuming
* zero proper motion and parallax.
* Language:
* Starlink ANSI C
* Type of Module:
* Library routine
* Invocation:
* palFk54z( double r2000, double d2000, double bepoch, double *r1950,
* double *d1950, double *dr1950, double *dd1950 )
* Arguments:
* r2000 = double (Given)
* J2000.0 FK5 RA (radians).
* d2000 = double (Given)
* J2000.0 FK5 Dec (radians).
* bepoch = double (Given)
* Besselian epoch (e.g. 1950.0).
* r1950 = double * (Returned)
* B1950 FK4 RA (radians) at epoch "bepoch".
* d1950 = double * (Returned)
* B1950 FK4 Dec (radians) at epoch "bepoch".
* dr1950 = double * (Returned)
* B1950 FK4 proper motion (RA) (radians/trop.yr)).
* dr1950 = double * (Returned)
* B1950 FK4 proper motion (Dec) (radians/trop.yr)).
* Description:
* This function converts star positions from the IAU 1976,
* FK5, Fricke system to the Bessel-Newcomb, FK4 system.
* Notes:
* - The proper motion in RA is dRA/dt rather than cos(Dec)*dRA/dt.
* - Conversion from Julian epoch 2000.0 to Besselian epoch 1950.0
* only is provided for. Conversions involving other epochs will
* require use of the appropriate precession functions before and
* after this function is called.
* - The FK5 proper motions, the parallax and the radial velocity
* are presumed zero.
* - It is the intention that FK5 should be a close approximation
* to an inertial frame, so that distant objects have zero proper
* motion; such objects have (in general) non-zero proper motion
* in FK4, and this function returns those fictitious proper
* motions.
* - The position returned by this function is in the B1950
* reference frame but at Besselian epoch BEPOCH. For comparison
* with catalogues the "bepoch" argument will frequently be 1950.0.
* Authors:
* PTW: Pat Wallace (STFC)
* DSB: David Berry (JAC, Hawaii)
* {enter_new_authors_here}
* History:
* 2012-02-13 (DSB):
* Initial version with documentation taken from Fortran SLA
* {enter_further_changes_here}
* Copyright:
* Copyright (C) 2012 Science and Technology Facilities Council.
* All Rights Reserved.
* Licence:
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 3 of
* the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be
* useful, but WITHOUT ANY WARRANTY; without even the implied
* warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
* PURPOSE. See the GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
* USA.
* Bugs:
* {note_any_bugs_here}
*-
*/
#include "pal.h"
#include "sofa.h"
void palFk54z( double r2000, double d2000, double bepoch, double *r1950,
double *d1950, double *dr1950, double *dd1950 ){
/* Local Variables: */
double r, d, px, rv, y;
/* FK5 equinox J2000 (any epoch) to FK4 equinox B1950 epoch B1950. */
palFk524( r2000, d2000, 0.0, 0.0, 0.0, 0.0, &r, &d, dr1950, dd1950,
&px, &rv );
/* Fictitious proper motion to epoch "bepoch". */
y = bepoch - 1950.0;
*r1950 = r + *dr1950*y;
*d1950 = d + *dd1950*y;
}