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slalib/eqeqx.f

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+      DOUBLE PRECISION FUNCTION sla_EQEQX (DATE)
+*+
+*     - - - - - -
+*      E Q E Q X
+*     - - - - - -
+*
+*  Equation of the equinoxes  (IAU 1994, double precision)
+*
+*  Given:
+*     DATE    dp      TDB (loosely ET) as Modified Julian Date
+*                                          (JD-2400000.5)
+*
+*  The result is the equation of the equinoxes (double precision)
+*  in radians:
+*
+*     Greenwich apparent ST = GMST + sla_EQEQX
+*
+*  References:  IAU Resolution C7, Recommendation 3 (1994)
+*               Capitaine, N. & Gontier, A.-M., Astron. Astrophys.,
+*               275, 645-650 (1993)
+*
+*  Called:  sla_NUTC
+*
+*  Patrick Wallace   Starlink   23 August 1996
+*
+*  Copyright (C) 1996 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 DATE
+
+*  Turns to arc seconds and arc seconds to radians
+      DOUBLE PRECISION T2AS,AS2R
+      PARAMETER (T2AS=1296000D0,
+     :           AS2R=0.484813681109535994D-5)
+
+      DOUBLE PRECISION T,OM,DPSI,DEPS,EPS0
+
+
+
+*  Interval between basic epoch J2000.0 and current epoch (JC)
+      T=(DATE-51544.5D0)/36525D0
+
+*  Longitude of the mean ascending node of the lunar orbit on the
+*   ecliptic, measured from the mean equinox of date
+      OM=AS2R*(450160.280D0+(-5D0*T2AS-482890.539D0
+     :         +(7.455D0+0.008D0*T)*T)*T)
+
+*  Nutation
+      CALL sla_NUTC(DATE,DPSI,DEPS,EPS0)
+
+*  Equation of the equinoxes
+      sla_EQEQX=DPSI*COS(EPS0)+AS2R*(0.00264D0*SIN(OM)+
+     :                               0.000063D0*SIN(OM+OM))
+
+      END