DOUBLE PRECISION FUNCTION iau_GMST82 ( DJ1, DJ2 ) *+ * - - - - - - - - - - - * i a u _ G M S T 8 2 * - - - - - - - - - - - * * Universal Time to Greenwich Mean Sidereal Time (IAU 1982 model). * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: canonical model. * * Given: * DJ1, DJ2 d UT1 Julian Date (see note) * * Returned: * iau_GMST82 d Greenwich mean sidereal time (radians) * * Notes: * * 1) The UT1 epoch 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 routine, 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. * * 4) The result is returned in the range 0 to 2pi. * * Called: * iau_ANP 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: 2017 October 12 * * SOFA release 2018-01-30 * * Copyright (C) 2018 IAU SOFA Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION DJ1, DJ2 * Seconds of time to radians DOUBLE PRECISION DS2R PARAMETER ( DS2R = 7.272205216643039903848712D-5 ) * Reference epoch (J2000.0), JD DOUBLE PRECISION DJ00 PARAMETER ( DJ00 = 2451545D0 ) * Seconds per day, days per Julian century DOUBLE PRECISION D2S, DJC PARAMETER ( D2S = 86400D0, DJC = 36525D0 ) * Coefficients of IAU 1982 GMST-UT1 model DOUBLE PRECISION A, B, C, D PARAMETER ( A = 24110.54841D0 - D2S/2D0, : B = 8640184.812866D0, : C = 0.093104D0, : D = -6.2D-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 PRECISION D1, D2, T, F DOUBLE PRECISION iau_ANP * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Julian centuries since fundamental epoch. IF ( DJ1 .LT. DJ2 ) THEN D1 = DJ1 D2 = DJ2 ELSE D1 = DJ2 D2 = DJ1 END IF T = ( D1 + ( D2-DJ00 ) ) / DJC * Fractional part of JD(UT1), in seconds. F = D2S * ( MOD(D1,1D0) + MOD(D2,1D0) ) * GMST at this UT1. iau_GMST82 = iau_ANP ( DS2R * ( (A+(B+(C+D*T)*T)*T) + F ) ) * Finished. *+---------------------------------------------------------------------- * * Copyright (C) 2018 * Standards Of Fundamental Astronomy Board * of the International Astronomical Union. * * ===================== * SOFA Software License * ===================== * * NOTICE TO USER: * * BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND * CONDITIONS WHICH APPLY TO ITS USE. * * 1. The Software is owned by the IAU SOFA Board ("SOFA"). * * 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 distribute SOFA source code to others, * and use and adapt its code and algorithms in your own software, * on a world-wide, royalty-free basis. That portion of your * distribution that does not consist of intact and unchanged copies * of SOFA source code files is a "derived work" that must comply * 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 itself constitute software provided by and/or * endorsed by SOFA. * * b) The source code of your derived work must contain descriptions * of how the derived work is based upon, contains and/or differs * from the original SOFA software. * * c) The names of all routines in your derived work shall not * include the prefix "iau" or "sofa" or trivial modifications * thereof such as changes of case. * * d) 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. * * e) 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. * * Note that, as originally distributed, the SOFA software is * intended to be a definitive implementation of the IAU standards, * and consequently third-party modifications are discouraged. All * variations, no matter how minor, must be explicitly marked as * such, as explained above. * * 4. You shall not cause the SOFA software to be brought into * disrepute, either by misuse, or use for inappropriate tasks, or * by inappropriate modification. * * 5. The SOFA software is provided "as is" and SOFA makes no warranty * as to its use or performance. SOFA does not and cannot warrant * the performance or results which the user may obtain by using the * SOFA software. SOFA 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 SOFA be * liable to the user for any consequential, incidental, or special * damages, including any lost profits or lost savings, even if a * SOFA representative has been advised of such damages, or for any * claim by any third party. * * 6. 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. * * In any published work or commercial product which uses the SOFA * software directly, acknowledgement (see www.iausofa.org) is * appreciated. * * Correspondence concerning SOFA software should be addressed as * follows: * * By email: sofa@ukho.gov.uk * By post: IAU SOFA Center * HM Nautical Almanac Office * UK Hydrographic Office * Admiralty Way, Taunton * Somerset, TA1 2DN * United Kingdom * *----------------------------------------------------------------------- END