/*
*+
* Name:
* palRdplan
* Purpose:
* Approximate topocentric apparent RA,Dec of a planet
* Language:
* Starlink ANSI C
* Type of Module:
* Library routine
* Invocation:
* void palRdplan( double date, int np, double elong, double phi,
* double * ra, double * dec, double * diam );
* Arguments:
* date = double (Given)
* MJD of observation (JD-2400000.5) in TDB. For all practical
* purposes TT can be used instead of TDB, and for many applications
* UT will do (except for the Moon).
* np = int (Given)
* Planet: 1 = Mercury
* 2 = Venus
* 3 = Moon
* 4 = Mars
* 5 = Jupiter
* 6 = Saturn
* 7 = Uranus
* 8 = Neptune
* else = Sun
* elong = double (Given)
* Observer's east longitude (radians)
* phi = double (Given)
* Observer's geodetic latitude (radians)
* ra = double * (Returned)
* RA (topocentric apparent, radians)
* dec = double * (Returned)
* Dec (topocentric apparent, radians)
* diam = double * (Returned)
* Angular diameter (equatorial, radians)
* Description:
* Approximate topocentric apparent RA,Dec of a planet, and its
* angular diameter.
* Authors:
* PTW: Patrick T. Wallace
* TIMJ: Tim Jenness (JAC, Hawaii)
* {enter_new_authors_here}
* Notes:
* - Unlike with slaRdplan, Pluto is not supported.
* - The longitude and latitude allow correction for geocentric
* parallax. This is a major effect for the Moon, but in the
* context of the limited accuracy of the present routine its
* effect on planetary positions is small (negligible for the
* outer planets). Geocentric positions can be generated by
* appropriate use of the routines palDmoon and eraPlan94.
* History:
* 2012-03-07 (TIMJ):
* Initial version, with some documentation from SLA/F.
* Adapted with permission from the Fortran SLALIB library.
* {enter_further_changes_here}
* Copyright:
* Copyright (C) 1997 Rutherford Appleton Laboratory
* 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 <math.h>
#include "pal.h"
#include "palmac.h"
#include "pal1sofa.h"
void palRdplan( double date, int np, double elong, double phi,
double * ra, double * dec, double * diam ) {
/* AU in km */
const double AUKM = 1.49597870e8;
/* Equatorial radii (km) */
const double EQRAU[] = {
696000.0, /* Sun */
2439.7,
6051.9,
1738,
3397,
71492,
60268,
25559,
24764
};
/* Local variables */
int i, j;
double stl;
double vgm[6];
double v[6];
double rmat[3][3];
double vse[6];
double vsg[6];
double vsp[6];
double vgo[6];
double dx,dy,dz,r,tl;
/* Classify np */
if (np < 0 || np > 8 ) np=0; /* Sun */
/* Approximate local sidereal time */
stl = palGmst( date - palDt( palEpj(date)) / 86400.0) + elong;
/* Geocentre to Moon (mean of date) */
palDmoon( date, v );
/* Nutation to true of date */
palNut( date, rmat );
eraRxp( rmat, v, vgm );
eraRxp( rmat, &(v[3]), &(vgm[3]) );
/* Moon? */
if (np == 3) {
/* geocentre to Moon (true of date) */
for (i=0; i<6; i++) {
v[i] = vgm[i];
}
} else {
/* Not moon: precession/nutation matrix J2000 to date */
palPrenut( 2000.0, date, rmat );
/* Sun to Earth-Moon Barycentre (J2000) */
palPlanet( date, 3, v, &j );
/* Precession and nutation to date */
eraRxp( rmat, v, vse );
eraRxp( rmat, &(v[3]), &(vse[3]) );
/* Sun to geocentre (true of date) */
for (i=0; i<6; i++) {
vsg[i] = vse[i] - 0.012150581 * vgm[i];
}
/* Sun ? */
if (np == 0) {
/* Geocentre to Sun */
for (i=0; i<6; i++) {
v[i] = -vsg[i];
}
} else {
/* Sun to Planet (J2000) */
palPlanet( date, np, v, &j );
/* Precession and nutation to date */
eraRxp( rmat, v, vsp );
eraRxp( rmat, &(v[3]), &(vsp[3]) );
/* Geocentre to planet */
for (i=0; i<6; i++) {
v[i] = vsp[i] - vsg[i];
}
}
}
/* Refer to origina at the observer */
palPvobs( phi, 0.0, stl, vgo );
for (i=0; i<6; i++) {
v[i] -= vgo[i];
}
/* Geometric distance (AU) */
dx = v[0];
dy = v[1];
dz = v[2];
r = sqrt( dx*dx + dy*dy + dz*dz );
/* Light time */
tl = PAL__CR * r;
/* Correct position for planetary aberration */
for (i=0; i<3; i++) {
v[i] -= tl * v[i+3];
}
/* To RA,Dec */
eraC2s( v, ra, dec );
*ra = eraAnp( *ra );
/* Angular diameter (radians) */
*diam = 2.0 * asin( EQRAU[np] / (r * AUKM ) );
}