[

define_tag: 'lp_date_GMST',
	-description='Returns Greenwich Mean Sidereal Time in radians given a Julian date.',
	-priority='replace',
	-required='JulianDate';

	// adapted from i a u _ G M S T 0 0
	// original Fortran version follows below

	local:'DJ' = (lp_date_juliansplit: #juliandate);
	local:'DJ1' = (decimal: #DJ->(find:'date'));
	local:'DJ2' = (decimal: #DJ->(find:'time'));

	// *  TT Julian centuries since J2000.0.
      local:'T' = ( ( #DJ1-2451545.0 ) + #DJ2 ) / 36525.0;

	// *  Greenwich Mean Sidereal Time, IAU 2000.
      return: lp_decimal_precisionset(lp_math_range2PI( lp_math_earthRotationAngle( #JulianDate ) +
                            (    0.014506   +
                            ( 4612.15739966 +
                            (  + 1.39667721 +
                            (  - 0.00009344 +
                            (  + 0.00001882 )
                                      * #T ) * #T ) * #T ) * #T ) * 0.000004848136811095359935899141 ));

	// test vector: http://zeitladen.de/time.html

/define_tag;

/*

      DOUBLE PRECISION FUNCTION iau_GMST00 ( UTA, UTB, TTA, TTB )
*+
*  - - - - - - - - - - -
*   i a u _ G M S T 0 0
*  - - - - - - - - - - -
*
*  Greenwich Mean Sidereal Time (model consistent with IAU 2000
*  resolutions).
*
*  This routine is part of the International Astronomical Union's
*  SOFA (Standards of Fundamental Astronomy) software collection.
*
*  Status:  canonical model.
*
*  Given:
*     UTA, UTB     d      UT1 as a 2-part Julian Date (Notes 1,2)
*     TTA, TTB     d      TT as a 2-part Julian Date (Notes 1,2)
*
*  The result is the Greenwich Mean Sidereal Time (radians), in the
*  range 0 to 2pi.
*
*  Notes:
*
*  1) The UT1 and TT dates UTA+UTB and TTA+TTB respectively, are both
*     Julian Dates, apportioned in any convenient way between the
*     argument pairs.  For example, JD=2450123.7 could be expressed in
*     any of these ways, among others:
*
*            Part A         Part B
*
*         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 (in the case of UT;  the TT is not at all critical
*     in this respect).  The J2000 and MJD methods are good compromises
*     between resolution and convenience.  For UT, the date & time
*     method is best matched to the algorithm that is used by the Earth
*     Rotation Angle routine, called internally:  maximum accuracy (or,
*     at least, minimum noise) is delivered when the UTA argument is for
*     0hrs UT1 on the day in question and the UTB argument lies in the
*     range 0 to 1, or vice versa.
*
*  2) Both UT1 and TT are required, UT1 to predict the Earth rotation
*     and TT to predict the effects of precession.  If UT1 is used for
*     both purposes, errors of order 100 microarcseconds result.
*
*  3) This GMST is compatible with the IAU 2000 resolutions and must be
*     used only in conjunction with other IAU 2000 compatible components
*     such as precession-nutation and equation of the equinoxes.
*
*  4) The algorithm is from Capitaine et al. (2003) and IERS Conventions
*     2003.
*
*  Called:
*     iau_ERA00      Earth Rotation Angle, IAU 2000
*     iau_ANP        normalize angle into range 0 to 2pi
*
*  References:
*
*     Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
*     implement the IAU 2000 definition of UT1", Astronomy &
*     Astrophysics, 406, 1135-1149 (2003)
*
*     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
*     IERS Technical Note No. 32, BKG (2004)
*
*  This revision:  2005 August 24
*
*  Copyright (C) 2005 IAU SOFA Review Board.  See notes at end.
*
*-----------------------------------------------------------------------

      IMPLICIT NONE

      DOUBLE PRECISION UTA, UTB, TTA, TTB

*  Arcseconds to radians
      DOUBLE PRECISION DAS2R
      PARAMETER ( DAS2R = 4.848136811095359935899141D-6 )

*  Reference epoch (J2000), JD
      DOUBLE PRECISION DJ0
      PARAMETER ( DJ0 = 2451545D0 )

*  Days per Julian century
      DOUBLE PRECISION DJC
      PARAMETER ( DJC = 36525D0 )

      DOUBLE PRECISION T

      DOUBLE PRECISION iau_ANP, iau_ERA00

* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

*  TT Julian centuries since J2000.0.
      T = ( ( TTA-DJ0 ) + TTB ) / DJC

*  Greenwich Mean Sidereal Time, IAU 2000.
      iau_GMST00 = iau_ANP ( iau_ERA00 ( UTA, UTB ) +
     :                       (    0.014506  D0 +
     :                       ( 4612.15739966D0 +
     :                       (  + 1.39667721D0 +
     :                       (  - 0.00009344D0 +
     :                       (  + 0.00001882D0 )
     :                                 * T ) * T ) * T ) * T ) * DAS2R )

*  Finished.

*+----------------------------------------------------------------------
*
*  Copyright (C) 2005
*  Standards Of Fundamental Astronomy Review Board
*  of the International Astronomical Union.
*
*  =====================
*  SOFA Software License
*  =====================
*
*  NOTICE TO USER:
*
*  BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING TERMS AND CONDITIONS
*  WHICH APPLY TO ITS USE.
*
*  1. The Software is owned by the IAU SOFA Review Board ("the Board").
*
*  2. The Software is made available free of charge for use by:
*
*     a) private individuals for non-profit research; and
*
*     b) non-profit educational, academic and research institutions.
*
*  3. Commercial use of the Software is specifically excluded from the
*     terms and conditions of this license.  Commercial use of the
*     Software is subject to the prior written agreement of the Board on
*     terms to be agreed.
*
*  4. The provision of any version of the Software under the terms and
*     conditions specified herein does not imply that future versions
*     will also be made available under the same terms and conditions.
*
*  5. The user may modify the Software for his/her own purposes.  The
*     user may distribute the modified software provided that the Board
*     is informed and that a copy of the modified software is made
*     available to the Board on request.  All modifications made by the
*     user shall be clearly identified to show how the modified software
*     differs from the original Software, and the name(s) of the
*     affected routine(s) shall be changed.  The original SOFA Software
*     License text must be present.
*
*  6. In any published work produced by the user and which includes
*     results achieved by using the Software, the user shall acknowledge
*     that the Software was used in producing the information contained
*     in such publication.
*
*  7. The user may incorporate or embed the Software into other software
*     products which he/she may then give away free of charge but not
*     sell provided the user makes due acknowledgement of the use which
*     he/she has made of the Software in creating such software
*     products.  Any redistribution of the Software in this way shall be
*     made under the same terms and conditions under which the user
*     received it from the SOFA Center.
*
*  8. The user shall not cause the Software to be brought into
*     disrepute, either by misuse, or use for inappropriate tasks, or by
*     inappropriate modification.
*
*  9. The Software is provided to the user "as is" and the Board makes
*     no warranty as to its use or performance.   The Board does not and
*     cannot warrant the performance or results which the user may
*     obtain by using the Software.  The Board makes no warranties,
*     express or implied, as to non-infringement of third party rights,
*     merchantability, or fitness for any particular purpose.  In no
*     event will the Board be liable to the user for any consequential,
*     incidental, or special damages, including any lost profits or lost
*     savings, even if a Board representative has been advised of such
*     damages, or for any claim by any third party.
*
*  Correspondence concerning SOFA software should be addressed as
*  follows:
*
*     Internet email: sofa@rl.ac.uk
*     Postal address: IAU SOFA Center
*                     Rutherford Appleton Laboratory
*                     Chilton, Didcot, Oxon OX11 0QX
*                     United Kingdom
*
*
*-----------------------------------------------------------------------

      END

*/

]