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89 lines
2.9 KiB
Fortran
89 lines
2.9 KiB
Fortran
SUBROUTINE sla_AMP (RA, DA, DATE, EQ, RM, DM)
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*+
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* - - - -
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* A M P
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* - - - -
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*
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* Convert star RA,Dec from geocentric apparent to mean place
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*
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* The mean coordinate system is the post IAU 1976 system,
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* loosely called FK5.
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*
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* Given:
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* RA d apparent RA (radians)
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* DA d apparent Dec (radians)
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* DATE d TDB for apparent place (JD-2400000.5)
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* EQ d equinox: Julian epoch of mean place
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*
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* Returned:
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* RM d mean RA (radians)
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* DM d mean Dec (radians)
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*
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* References:
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* 1984 Astronomical Almanac, pp B39-B41.
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* (also Lederle & Schwan, Astron. Astrophys. 134,
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* 1-6, 1984)
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*
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* Notes:
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*
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* 1) The distinction between the required TDB and TT is always
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* negligible. Moreover, for all but the most critical
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* applications UTC is adequate.
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*
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* 2) Iterative techniques are used for the aberration and light
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* deflection corrections so that the routines sla_AMP (or
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* sla_AMPQK) and sla_MAP (or sla_MAPQK) are accurate inverses;
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* even at the edge of the Sun's disc the discrepancy is only
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* about 1 nanoarcsecond.
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*
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* 3) Where multiple apparent places are to be converted to mean
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* places, for a fixed date and equinox, it is more efficient to
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* use the sla_MAPPA routine to compute the required parameters
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* once, followed by one call to sla_AMPQK per star.
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*
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* 4) The accuracy is sub-milliarcsecond, limited by the
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* precession-nutation model (IAU 1976 precession, Shirai &
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* Fukushima 2001 forced nutation and precession corrections).
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*
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* 5) The accuracy is further limited by the routine sla_EVP, called
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* by sla_MAPPA, which computes the Earth position and velocity
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* using the methods of Stumpff. The maximum error is about
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* 0.3 mas.
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*
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* Called: sla_MAPPA, sla_AMPQK
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*
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* P.T.Wallace Starlink 17 September 2001
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*
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* Copyright (C) 2001 Rutherford Appleton Laboratory
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*
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* License:
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program (see SLA_CONDITIONS); if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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* Boston, MA 02111-1307 USA
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*
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*-
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IMPLICIT NONE
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DOUBLE PRECISION RA,DA,DATE,EQ,RM,DM
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DOUBLE PRECISION AMPRMS(21)
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CALL sla_MAPPA(EQ,DATE,AMPRMS)
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CALL sla_AMPQK(RA,DA,AMPRMS,RM,DM)
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END
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