SUBROUTINE iau_TDBTCB ( TDB1, TDB2, TCB1, TCB2, J ) *+ * - - - - - - - - - - - * i a u _ T D B T C B * - - - - - - - - - - - * * Time scale transformation: Barycentric Dynamical Time, TDB, to * Barycentric Coordinate Time, TCB. * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: canonical. * * Given: * TDB1,TDB2 d TDB as a 2-part Julian Date * * Returned: * TCB1,TCB2 d TCB as a 2-part Julian Date * J i status: 0 = OK * * Notes: * * 1) TDB1+TDB2 is Julian Date, apportioned in any convenient way * between the two arguments, for example where TDB1 is the Julian * Day Number and TDB2 is the fraction of a day. The returned * TCB1,TCB2 follow suit. * * 2) The 2006 IAU General Assembly introduced a conventional linear * transformation between TDB and TCB. This transformation * compensates for the drift between TCB and terrestrial time TT, * and keeps TDB approximately centered on TT. Because the * relationship between TT and TCB depends on the adopted solar * system ephemeris, the degree of alignment between TDB and TT over * long intervals will vary according to which ephemeris is used. * Former definitions of TDB attempted to avoid this problem by * stipulating that TDB and TT should differ only by periodic * effects. This is a good description of the nature of the * relationship but eluded precise mathematical formulation. The * conventional linear relationship adopted in 2006 sidestepped * these difficulties whilst delivering a TDB that in practice was * consistent with values before that date. * * 3) TDB is essentially the same as Teph, the time argument for the * JPL solar system ephemerides. * * Reference: * * IAU 2006 Resolution B3 * * This revision: 2019 June 20 * * SOFA release 2023-10-11 * * Copyright (C) 2023 IAU SOFA Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION TDB1, TDB2, TCB1, TCB2 INTEGER J * 1977 Jan 1.0 TAI = 1977/1/1 00:00:32.184 TCB, as two-part JD DOUBLE PRECISION T77TD, T77TF PARAMETER ( T77TD = 2443144D0, : T77TF = 0.5003725D0 ) * L_B, and TDB0 (d) DOUBLE PRECISION ELB, TDB0 PARAMETER ( ELB = 1.550519768D-8, : TDB0 = -6.55D-5/86400D0 ) * TDB to TCB rate DOUBLE PRECISION ELBB PARAMETER ( ELBB = ELB/(1D0-ELB) ) DOUBLE PRECISION D, F * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Result, preserving date format but safeguarding precision. IF ( ABS(TDB1).GT.ABS(TDB2) ) THEN D = T77TD - TDB1 F = TDB2 - TDB0 TCB1 = TDB1 TCB2 = F - ( D - ( F - T77TF ) ) * ELBB ELSE D = T77TD - TDB2 F = TDB1 - TDB0 TCB1 = F - ( D - ( F - T77TF ) ) * ELBB TCB2 = TDB2 END IF * Status (always OK). J = 0 * Finished. *+---------------------------------------------------------------------- * * Copyright (C) 2023 * 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