SUBROUTINE iau_PREC76 ( EP01, EP02, EP11, EP12, ZETA, Z, THETA ) *+ * - - - - - - - - - - - * i a u _ P R E C 7 6 * - - - - - - - - - - - * * IAU 1976 precession model. * * This routine forms the three Euler angles which implement general * precession between two epochs, using the IAU 1976 model (as for * the FK5 catalog). * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: canonical model. * * Given: * EP01,EP02 d TDB starting epoch (Note 1) * EP11,EP12 d TDB ending epoch (Note 1) * * Returned: * ZETA d 1st rotation: radians clockwise around z * Z d 3rd rotation: radians clockwise around z * THETA d 2nd rotation: radians counterclockwise around y * * Notes: * * 1) The epochs EP01+EP02 and EP11+EP12 are Julian Dates, apportioned * in any convenient way between the arguments EPn1 and EPn2. For * example, JD(TDB)=2450123.7 could be expressed in any of these * ways, among others: * * EPn1 EPn2 * * 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 method is best matched to the way the * argument is handled internally and will deliver the optimum * optimum resolution. The MJD method and the date & time methods * are both good compromises between resolution and convenience. * The two epochs may be expressed using different methods, but at * the risk of losing some resolution. * * 2) The accumulated precession angles zeta, z, theta are expressed * through canonical polynomials which are valid only for a limited * time span. In addition, the IAU 1976 precession rate is known to * be imperfect. The absolute accuracy of the present formulation is * better than 0.1 arcsec from 1960AD to 2040AD, better than 1 arcsec * from 1640AD to 2360AD, and remains below 3 arcsec for the whole of * the period 500BC to 3000AD. The errors exceed 10 arcsec outside * the range 1200BC to 3900AD, exceed 100 arcsec outside 4200BC to * 5600AD and exceed 1000 arcsec 1000 arcsec outside 6800BC to * 8200AD. * * 3) The three angles are returned in the conventional order, which * is not the same as the order of the corresponding Euler rotations. * The precession matrix is R_3(-z) x R_2(+theta) x R_3(-zeta). * * References: * Lieske,J.H., 1979. Astron.Astrophys.,73,282. * equations (6) & (7), p283. * * This revision: 2000 November 25 * * Copyright (C) 2001 IAU SOFA Review Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION EP01, EP02, EP11, EP12, ZETA, Z, THETA * 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 T0, T, TAS2R, W * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Interval between fundamental epoch J2000.0 and beginning epoch (JC). T0 = ( ( EP01-DJ0 ) + EP02 ) / DJC * Interval over which precession required (JC). T = ( ( EP11-EP01 ) + ( EP12-EP02 ) ) / DJC * Euler angles. TAS2R = T * DAS2R W = 2306.2181D0 + ( : 1.39656D0 : - 0.000139D0 * T0 ) * T0 ZETA = ( W + ( ( 0.30188D0 : - 0.000344D0 * T0 ) : + 0.017998D0 * T ) * T ) * TAS2R Z = ( W + ( ( 1.09468D0 : + 0.000066D0 * T0 ) : + 0.018203D0 * T ) * T ) * TAS2R THETA = ( ( 2004.3109D0 + ( : - 0.85330D0 : - 0.000217D0 * T0 ) * T0 ) + ( ( : - 0.42665D0 : - 0.000217D0 * T0 ) : - 0.041833D0 * T ) * T ) * TAS2R * Finished. *+---------------------------------------------------------------------- * * Copyright (C) 2001 * 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