#include "sofa.h" double iauGst00a(double uta, double utb, double tta, double ttb) /* ** - - - - - - - - - - ** i a u G s t 0 0 a ** - - - - - - - - - - ** ** Greenwich apparent sidereal time (consistent with IAU 2000 ** resolutions). ** ** This function is part of the International Astronomical Union's ** SOFA (Standards Of Fundamental Astronomy) software collection. ** ** Status: canonical model. ** ** Given: ** uta,utb double UT1 as a 2-part Julian Date (Notes 1,2) ** tta,ttb double TT as a 2-part Julian Date (Notes 1,2) ** ** Returned (function value): ** double Greenwich apparent sidereal time (radians) ** ** 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(UT1)=2450123.7 could be ** expressed in any of these ways, among others: ** ** uta utb ** ** 2450123.7 0.0 (JD method) ** 2451545.0 -1421.3 (J2000 method) ** 2400000.5 50123.2 (MJD method) ** 2450123.5 0.2 (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 function, called internally: maximum precision 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-nutation. If UT1 is ** used for both purposes, errors of order 100 microarcseconds ** result. ** ** 3) This GAST is compatible with the IAU 2000 resolutions and must be ** used only in conjunction with other IAU 2000 compatible ** components such as precession-nutation. ** ** 4) The result is returned in the range 0 to 2pi. ** ** 5) The algorithm is from Capitaine et al. (2003) and IERS ** Conventions 2003. ** ** Called: ** iauGmst00 Greenwich mean sidereal time, IAU 2000 ** iauEe00a equation of the equinoxes, IAU 2000A ** iauAnp 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: 2021 May 11 ** ** SOFA release 2021-05-12 ** ** Copyright (C) 2021 IAU SOFA Board. See notes at end. */ { double gmst00, ee00a, gst; gmst00 = iauGmst00(uta, utb, tta, ttb); ee00a = iauEe00a(tta, ttb); gst = iauAnp(gmst00 + ee00a); return gst; /* Finished. */ /*---------------------------------------------------------------------- ** ** Copyright (C) 2021 ** 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 ** **--------------------------------------------------------------------*/ }