SUBROUTINE iau_PFW06 ( DATE1, DATE2, GAMB, PHIB, PSIB, EPSA )
*+
* - - - - - - - - - -
* i a u _ P F W 0 6
* - - - - - - - - - -
*
* Precession angles, IAU 2006 (Fukushima-Williams 4-angle formulation).
*
* This routine is part of the International Astronomical Union's
* SOFA (Standards of Fundamental Astronomy) software collection.
*
* Status: canonical model.
*
* Given:
* DATE1,DATE2 d TT as a 2-part Julian Date (Note 1)
*
* Returned:
* GAMB d F-W angle gamma_bar (radians)
* PHIB d F-W angle phi_bar (radians)
* PSIB d F-W angle psi_bar (radians)
* EPSA d F-W angle epsilon_A (radians)
*
* Notes:
*
* 1) The TT date DATE1+DATE2 is a Julian Date, apportioned in any
* convenient way between the two arguments. For example,
* JD(TT)=2450123.7 could be expressed in any of these ways,
* among others
*
* DATE1 DATE2
*
* 2450123.7D0 0D0 (JD method)
* 2451545D0 -1421.3D0 (J2000 method)
* 2400000.5D0 50123.2D0 (MJD method)
* 2450123.5D0 0.2D0 (date & time method)
*
* The JD method is the most natural and convenient to use in
* cases where the loss of several decimal digits of resolution
* is acceptable. The J2000 method is best matched to the way
* the argument is handled internally and will deliver the
* optimum resolution. The MJD method and the date & time methods
* are both good compromises between resolution and convenience.
*
* 2) Naming the following points:
*
* e = J2000.0 ecliptic pole,
* p = GCRS pole,
* E = mean ecliptic pole of date,
* and P = mean pole of date,
*
* the four Fukushima-Williams angles are as follows:
*
* GAMB = gamma_bar = epE
* PHIB = phi_bar = pE
* PSIB = psi_bar = pEP
* EPSA = epsilon_A = EP
*
* 3) The matrix representing the combined effects of frame bias and
* precession is:
*
* PxB = R_1(-EPSA).R_3(-PSIB).R_1(PHIB).R_3(GAMB)
*
* 4) The matrix representing the combined effects of frame bias,
* precession and nutation is simply:
*
* NxPxB = R_1(-EPSA-dE).R_3(-PSIB-dP).R_1(PHIB).R_3(GAMB)
*
* where dP and dE are the nutation components with respect to the
* ecliptic of date.
*
* Reference:
*
* Hilton, J. et al., 2006, Celest.Mech.Dyn.Astron. 94, 351
*
* Called:
* iau_OBL06 mean obliquity, IAU 2006
*
* This revision: 2009 December 15
*
* SOFA release 2021-05-12
*
* Copyright (C) 2021 IAU SOFA Board. See notes at end.
*
*-----------------------------------------------------------------------
IMPLICIT NONE
DOUBLE PRECISION DATE1, DATE2, GAMB, PHIB, PSIB, EPSA
* Arcseconds to radians
DOUBLE PRECISION DAS2R
PARAMETER ( DAS2R = 4.848136811095359935899141D-6 )
* Reference epoch (J2000.0), JD
DOUBLE PRECISION DJ00
PARAMETER ( DJ00 = 2451545D0 )
* Days per Julian century
DOUBLE PRECISION DJC
PARAMETER ( DJC = 36525D0 )
DOUBLE PRECISION T
DOUBLE PRECISION iau_OBL06
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Interval between fundamental date J2000.0 and given date (JC).
T = ( ( DATE1-DJ00 ) + DATE2 ) / DJC
* P03 bias+precession angles.
GAMB = ( -0.052928D0 +
: ( 10.556378D0 +
: ( 0.4932044D0 +
: ( -0.00031238D0 +
: ( -0.000002788D0 +
: ( 0.0000000260D0 )
: * T ) * T ) * T ) * T ) * T ) * DAS2R
PHIB = ( 84381.412819D0 +
: ( -46.811016D0 +
: ( 0.0511268D0 +
: ( 0.00053289D0 +
: ( -0.000000440D0 +
: ( -0.0000000176D0 )
: * T ) * T ) * T ) * T ) * T ) * DAS2R
PSIB = ( -0.041775D0 +
: ( 5038.481484D0 +
: ( 1.5584175D0 +
: ( -0.00018522D0 +
: ( -0.000026452D0 +
: ( -0.0000000148D0 )
: * T ) * T ) * T ) * T ) * T ) * DAS2R
EPSA = iau_OBL06 ( DATE1, DATE2 )
* Finished.
*+----------------------------------------------------------------------
*
* Copyright (C) 2021
* Standards Of Fundamental Astronomy Board
* of the International Astronomical Union.
*
* =====================
* SOFA Software License
* =====================
*
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*
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*
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*
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*
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*
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*
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*
*-----------------------------------------------------------------------
END