#include "sofam.h"
double iauGmst82(double dj1, double dj2)
/*
** - - - - - - - - - -
** i a u G m s t 8 2
** - - - - - - - - - -
**
** Universal Time to Greenwich mean sidereal time (IAU 1982 model).
**
** This function is part of the International Astronomical Union's
** SOFA (Standards Of Fundamental Astronomy) software collection.
**
** Status: canonical model.
**
** Given:
** dj1,dj2 double UT1 Julian Date (see note)
**
** Returned (function value):
** double Greenwich mean sidereal time (radians)
**
** Notes:
**
** 1) The UT1 date dj1+dj2 is a Julian Date, apportioned in any
** convenient way between the arguments dj1 and dj2. For example,
** JD(UT1)=2450123.7 could be expressed in any of these ways,
** among others:
**
** dj1 dj2
**
** 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 and MJD methods are good compromises
** between resolution and convenience. The date & time method is
** best matched to the algorithm used: maximum accuracy (or, at
** least, minimum noise) is delivered when the dj1 argument is for
** 0hrs UT1 on the day in question and the dj2 argument lies in the
** range 0 to 1, or vice versa.
**
** 2) The algorithm is based on the IAU 1982 expression. This is
** always described as giving the GMST at 0 hours UT1. In fact, it
** gives the difference between the GMST and the UT, the steady
** 4-minutes-per-day drawing-ahead of ST with respect to UT. When
** whole days are ignored, the expression happens to equal the GMST
** at 0 hours UT1 each day.
**
** 3) In this function, the entire UT1 (the sum of the two arguments
** dj1 and dj2) is used directly as the argument for the standard
** formula, the constant term of which is adjusted by 12 hours to
** take account of the noon phasing of Julian Date. The UT1 is then
** added, but omitting whole days to conserve accuracy.
**
** Called:
** iauAnp normalize angle into range 0 to 2pi
**
** References:
**
** Transactions of the International Astronomical Union,
** XVIII B, 67 (1983).
**
** Aoki et al., Astron. Astrophys. 105, 359-361 (1982).
**
** This revision: 2008 May 24
**
** Copyright (C) 2008 IAU SOFA Review Board. See notes at end.
*/
{
/* Coefficients of IAU 1982 GMST-UT1 model */
double A = 24110.54841 - DAYSEC / 2.0;
double B = 8640184.812866;
double C = 0.093104;
double D = -6.2e-6;
/* Note: the first constant, A, has to be adjusted by 12 hours */
/* because the UT1 is supplied as a Julian date, which begins */
/* at noon. */
double d1, d2, t, f, gmst;
/* Julian centuries since fundamental epoch. */
if (dj1 < dj2) {
d1 = dj1;
d2 = dj2;
} else {
d1 = dj2;
d2 = dj1;
}
t = (d1 + (d2 - DJ00)) / DJC;
/* Fractional part of JD(UT1), in seconds. */
f = DAYSEC * (fmod(d1, 1.0) + fmod(d2, 1.0));
/* GMST at this UT1. */
gmst = iauAnp(DS2R * ((A + (B + (C + D * t) * t) * t) + f));
return gmst;
/*-----------------------------------------------------------------------
**
** Copyright (C) 2008
** 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. Permission is granted to anyone to use the SOFA software for any
** purpose, including commercial applications, free of charge and
** without payment of royalties, subject to the conditions and
** restrictions listed below.
**
** 3. You (the user) may copy and adapt the SOFA software and its
** algorithms for your own purposes and you may copy and distribute
** a resulting "derived work" to others on a world-wide, royalty-free
** basis, provided that the derived work complies with the following
** requirements:
**
** a) Your work shall be marked or carry a statement that it (i) uses
** routines and computations derived by you from software provided
** by SOFA under license to you; and (ii) does not contain
** software provided by SOFA or software that has been distributed
** by or endorsed by SOFA.
**
** b) The source code of your derived work must contain descriptions
** of how the derived work is based upon and/or differs from the
** original SOFA software.
**
** c) The name(s) of all routine(s) that you distribute shall differ
** from the SOFA names, even when the SOFA content has not been
** otherwise changed.
**
** d) The routine-naming prefix "iau" shall not be used.
**
** e) The origin of the SOFA components of your derived work must not
** be misrepresented; you must not claim that you wrote the
** original software, nor file a patent application for SOFA
** software or algorithms embedded in the SOFA software.
**
** f) These requirements must be reproduced intact in any source
** distribution and shall apply to anyone to whom you have granted
** a further right to modify the source code of your derived work.
**
** 4. In any published work or commercial products which includes
** results achieved by using the SOFA software, you shall acknowledge
** that the SOFA software was used in obtaining those results.
**
** 5. You shall not cause the SOFA software to be brought into
** disrepute, either by misuse, or use for inappropriate tasks, or by
** inappropriate modification.
**
** 6. The SOFA software is provided "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 SOFA 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.
**
** 7. The provision of any version of the SOFA 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.
**
** 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
**
**---------------------------------------------------------------------*/
}