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Diffstat (limited to 'ast/erfa/gst94.c')
| -rw-r--r-- | ast/erfa/gst94.c | 140 |
1 files changed, 140 insertions, 0 deletions
diff --git a/ast/erfa/gst94.c b/ast/erfa/gst94.c new file mode 100644 index 0000000..79f7ba8 --- /dev/null +++ b/ast/erfa/gst94.c @@ -0,0 +1,140 @@ +#include "erfa.h" + +double eraGst94(double uta, double utb) +/* +** - - - - - - - - - +** e r a G s t 9 4 +** - - - - - - - - - +** +** Greenwich apparent sidereal time (consistent with IAU 1982/94 +** resolutions). +** +** Given: +** uta,utb double UT1 as a 2-part Julian Date (Notes 1,2) +** +** Returned (function value): +** double Greenwich apparent sidereal time (radians) +** +** Notes: +** +** 1) The UT1 date uta+utb is a Julian Date, apportioned in any +** convenient way between the argument pair. For example, +** JD=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. 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) The result is compatible with the IAU 1982 and 1994 resolutions, +** except that accuracy has been compromised for the sake of +** convenience in that UT is used instead of TDB (or TT) to compute +** the equation of the equinoxes. +** +** 3) This GAST must be used only in conjunction with contemporaneous +** IAU standards such as 1976 precession, 1980 obliquity and 1982 +** nutation. It is not compatible with the IAU 2000 resolutions. +** +** 4) The result is returned in the range 0 to 2pi. +** +** Called: +** eraGmst82 Greenwich mean sidereal time, IAU 1982 +** eraEqeq94 equation of the equinoxes, IAU 1994 +** eraAnp normalize angle into range 0 to 2pi +** +** References: +** +** Explanatory Supplement to the Astronomical Almanac, +** P. Kenneth Seidelmann (ed), University Science Books (1992) +** +** IAU Resolution C7, Recommendation 3 (1994) +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double gmst82, eqeq94, gst; + + + gmst82 = eraGmst82(uta, utb); + eqeq94 = eraEqeq94(uta, utb); + gst = eraAnp(gmst82 + eqeq94); + + return gst; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** All rights reserved. +** +** This library is derived, with permission, from the International +** Astronomical Union's "Standards of Fundamental Astronomy" library, +** available from http://www.iausofa.org. +** +** The ERFA version is intended to retain identical functionality to +** the SOFA library, but made distinct through different function and +** file names, as set out in the SOFA license conditions. The SOFA +** original has a role as a reference standard for the IAU and IERS, +** and consequently redistribution is permitted only in its unaltered +** state. The ERFA version is not subject to this restriction and +** therefore can be included in distributions which do not support the +** concept of "read only" software. +** +** Although the intent is to replicate the SOFA API (other than +** replacement of prefix names) and results (with the exception of +** bugs; any that are discovered will be fixed), SOFA is not +** responsible for any errors found in this version of the library. +** +** If you wish to acknowledge the SOFA heritage, please acknowledge +** that you are using a library derived from SOFA, rather than SOFA +** itself. +** +** +** TERMS AND CONDITIONS +** +** Redistribution and use in source and binary forms, with or without +** modification, are permitted provided that the following conditions +** are met: +** +** 1 Redistributions of source code must retain the above copyright +** notice, this list of conditions and the following disclaimer. +** +** 2 Redistributions in binary form must reproduce the above copyright +** notice, this list of conditions and the following disclaimer in +** the documentation and/or other materials provided with the +** distribution. +** +** 3 Neither the name of the Standards Of Fundamental Astronomy Board, +** the International Astronomical Union nor the names of its +** contributors may be used to endorse or promote products derived +** from this software without specific prior written permission. +** +** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS +** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE +** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, +** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, +** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; +** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER +** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN +** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +** POSSIBILITY OF SUCH DAMAGE. +** +*/ |