SUBROUTINE sla_AMP (RA, DA, DATE, EQ, RM, DM) *+ * - - - - * A M P * - - - - * * Convert star RA,Dec from geocentric apparent to mean place * * The mean coordinate system is the post IAU 1976 system, * loosely called FK5. * * Given: * RA d apparent RA (radians) * DA d apparent Dec (radians) * DATE d TDB for apparent place (JD-2400000.5) * EQ d equinox: Julian epoch of mean place * * Returned: * RM d mean RA (radians) * DM d mean Dec (radians) * * References: * 1984 Astronomical Almanac, pp B39-B41. * (also Lederle & Schwan, Astron. Astrophys. 134, * 1-6, 1984) * * Notes: * * 1) The distinction between the required TDB and TT is always * negligible. Moreover, for all but the most critical * applications UTC is adequate. * * 2) Iterative techniques are used for the aberration and light * deflection corrections so that the routines sla_AMP (or * sla_AMPQK) and sla_MAP (or sla_MAPQK) are accurate inverses; * even at the edge of the Sun's disc the discrepancy is only * about 1 nanoarcsecond. * * 3) Where multiple apparent places are to be converted to mean * places, for a fixed date and equinox, it is more efficient to * use the sla_MAPPA routine to compute the required parameters * once, followed by one call to sla_AMPQK per star. * * 4) The accuracy is sub-milliarcsecond, limited by the * precession-nutation model (IAU 1976 precession, Shirai & * Fukushima 2001 forced nutation and precession corrections). * * 5) The accuracy is further limited by the routine sla_EVP, called * by sla_MAPPA, which computes the Earth position and velocity * using the methods of Stumpff. The maximum error is about * 0.3 mas. * * Called: sla_MAPPA, sla_AMPQK * * P.T.Wallace Starlink 17 September 2001 * * Copyright (C) 2001 Rutherford Appleton Laboratory * * License: * 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 2 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 (see SLA_CONDITIONS); if not, write to the * Free Software Foundation, Inc., 59 Temple Place, Suite 330, * Boston, MA 02111-1307 USA * *- IMPLICIT NONE DOUBLE PRECISION RA,DA,DATE,EQ,RM,DM DOUBLE PRECISION AMPRMS(21) CALL sla_MAPPA(EQ,DATE,AMPRMS) CALL sla_AMPQK(RA,DA,AMPRMS,RM,DM) END