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76 lines
2.3 KiB
Fortran
76 lines
2.3 KiB
Fortran
SUBROUTINE sla_NUT (DATE, RMATN)
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*+
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* - - - -
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* N U T
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* - - - -
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*
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* Form the matrix of nutation for a given date - Shirai & Fukushima
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* 2001 theory (double precision)
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*
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* Reference:
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* Shirai, T. & Fukushima, T., Astron.J. 121, 3270-3283 (2001).
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*
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* Given:
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* DATE d TDB (loosely ET) as Modified Julian Date
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* (=JD-2400000.5)
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* Returned:
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* RMATN d(3,3) nutation matrix
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*
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* Notes:
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*
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* 1 The matrix is in the sense v(true) = rmatn * v(mean) .
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* where v(true) is the star vector relative to the true equator and
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* equinox of date and v(mean) is the star vector relative to the
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* mean equator and equinox of date.
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*
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* 2 The matrix represents forced nutation (but not free core
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* nutation) plus corrections to the IAU~1976 precession model.
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*
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* 3 Earth attitude predictions made by combining the present nutation
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* matrix with IAU~1976 precession are accurate to 1~mas (with
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* respect to the ICRS) for a few decades around 2000.
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*
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* 4 The distinction between the required TDB and TT is always
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* negligible. Moreover, for all but the most critical applications
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* UTC is adequate.
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*
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* Called: sla_NUTC, sla_DEULER
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*
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* Last revision: 1 December 2005
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*
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* Copyright P.T.Wallace. All rights reserved.
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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 DATE,RMATN(3,3)
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DOUBLE PRECISION DPSI,DEPS,EPS0
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* Nutation components and mean obliquity
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CALL sla_NUTC(DATE,DPSI,DEPS,EPS0)
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* Rotation matrix
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CALL sla_DEULER('XZX',EPS0,-DPSI,-(EPS0+DEPS),RMATN)
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END
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