|Posted||21 Apr 2006|
|Updated||21 Apr 2006|
|More by this author...|
Returns Greenwich Mean Sidereal Time in radians given a Julian date.
Requires [lp_date_juliansplit] [lp_decimal_precisionset] [lp_math_range2PI] [lp_math_earthRotationAngle]
var:'jd' = (lp_date_JulianDate: (date:'2006-02-01 18:00:00 GMT')); $jd;'
'; var:'t' = lp_date_gmst: $jd; $t; '
'; lp_math_degtohms:(lp_math_radtodeg: $t); // returns: // 2453768.25 // 0.72956728478705613 // 02:47:12
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[ 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: email@example.com * Postal address: IAU SOFA Center * Rutherford Appleton Laboratory * Chilton, Didcot, Oxon OX11 0QX * United Kingdom * * *----------------------------------------------------------------------- END */ ]