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: 2008 May 24 * * Copyright (C) 2008 IAU SOFA Review Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION DJ1, DJ2 DOUBLE PRECISION DS2R PARAMETER ( DS2R = 7.272205216643039903848712D-5 ) * Reference epoch (J2000), 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) 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 * *----------------------------------------------------------------------- END