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SUBROUTINE sla_ECMAT (DATE, RMAT)
*+
* - - - - - -
* E C M A T
* - - - - - -
*
* Form the equatorial to ecliptic rotation matrix - IAU 1980 theory
* (double precision)
*
* Given:
* DATE dp TDB (loosely ET) as Modified Julian Date
* (JD-2400000.5)
* Returned:
* RMAT dp(3,3) matrix
*
* Reference:
* Murray,C.A., Vectorial Astrometry, section 4.3.
*
* Note:
* The matrix is in the sense V(ecl) = RMAT * V(equ); the
* equator, equinox and ecliptic are mean of date.
*
* Called: sla_DEULER
*
* P.T.Wallace Starlink 23 August 1996
*
* Copyright (C) 1996 Rutherford Appleton Laboratory
*-
IMPLICIT NONE
DOUBLE PRECISION DATE,RMAT(3,3)
* Arc seconds to radians
DOUBLE PRECISION AS2R
PARAMETER (AS2R=0.484813681109535994D-5)
DOUBLE PRECISION T,EPS0
* Interval between basic epoch J2000.0 and current epoch (JC)
T = (DATE-51544.5D0)/36525D0
* Mean obliquity
EPS0 = AS2R*
: (84381.448D0+(-46.8150D0+(-0.00059D0+0.001813D0*T)*T)*T)
* Matrix
CALL sla_DEULER('X',EPS0,0D0,0D0,RMAT)
END
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