source: trunk/FACT++/erfa/src/gst94.c@ 18409

Last change on this file since 18409 was 18348, checked in by tbretz, 10 years ago
File size: 5.5 KB
Line 
1#include "erfa.h"
2
3double eraGst94(double uta, double utb)
4/*
5** - - - - - - - - -
6** e r a G s t 9 4
7** - - - - - - - - -
8**
9** Greenwich apparent sidereal time (consistent with IAU 1982/94
10** resolutions).
11**
12** Given:
13** uta,utb double UT1 as a 2-part Julian Date (Notes 1,2)
14**
15** Returned (function value):
16** double Greenwich apparent sidereal time (radians)
17**
18** Notes:
19**
20** 1) The UT1 date uta+utb is a Julian Date, apportioned in any
21** convenient way between the argument pair. For example,
22** JD=2450123.7 could be expressed in any of these ways, among
23** others:
24**
25** uta utb
26**
27** 2450123.7 0.0 (JD method)
28** 2451545.0 -1421.3 (J2000 method)
29** 2400000.5 50123.2 (MJD method)
30** 2450123.5 0.2 (date & time method)
31**
32** The JD method is the most natural and convenient to use in cases
33** where the loss of several decimal digits of resolution is
34** acceptable. The J2000 and MJD methods are good compromises
35** between resolution and convenience. For UT, the date & time
36** method is best matched to the algorithm that is used by the Earth
37** Rotation Angle function, called internally: maximum precision is
38** delivered when the uta argument is for 0hrs UT1 on the day in
39** question and the utb argument lies in the range 0 to 1, or vice
40** versa.
41**
42** 2) The result is compatible with the IAU 1982 and 1994 resolutions,
43** except that accuracy has been compromised for the sake of
44** convenience in that UT is used instead of TDB (or TT) to compute
45** the equation of the equinoxes.
46**
47** 3) This GAST must be used only in conjunction with contemporaneous
48** IAU standards such as 1976 precession, 1980 obliquity and 1982
49** nutation. It is not compatible with the IAU 2000 resolutions.
50**
51** 4) The result is returned in the range 0 to 2pi.
52**
53** Called:
54** eraGmst82 Greenwich mean sidereal time, IAU 1982
55** eraEqeq94 equation of the equinoxes, IAU 1994
56** eraAnp normalize angle into range 0 to 2pi
57**
58** References:
59**
60** Explanatory Supplement to the Astronomical Almanac,
61** P. Kenneth Seidelmann (ed), University Science Books (1992)
62**
63** IAU Resolution C7, Recommendation 3 (1994)
64**
65** Copyright (C) 2013-2015, NumFOCUS Foundation.
66** Derived, with permission, from the SOFA library. See notes at end of file.
67*/
68{
69 double gmst82, eqeq94, gst;
70
71 gmst82 = eraGmst82(uta, utb);
72 eqeq94 = eraEqeq94(uta, utb);
73 gst = eraAnp(gmst82 + eqeq94);
74
75 return gst;
76
77}
78/*----------------------------------------------------------------------
79**
80**
81** Copyright (C) 2013-2015, NumFOCUS Foundation.
82** All rights reserved.
83**
84** This library is derived, with permission, from the International
85** Astronomical Union's "Standards of Fundamental Astronomy" library,
86** available from http://www.iausofa.org.
87**
88** The ERFA version is intended to retain identical functionality to
89** the SOFA library, but made distinct through different function and
90** file names, as set out in the SOFA license conditions. The SOFA
91** original has a role as a reference standard for the IAU and IERS,
92** and consequently redistribution is permitted only in its unaltered
93** state. The ERFA version is not subject to this restriction and
94** therefore can be included in distributions which do not support the
95** concept of "read only" software.
96**
97** Although the intent is to replicate the SOFA API (other than
98** replacement of prefix names) and results (with the exception of
99** bugs; any that are discovered will be fixed), SOFA is not
100** responsible for any errors found in this version of the library.
101**
102** If you wish to acknowledge the SOFA heritage, please acknowledge
103** that you are using a library derived from SOFA, rather than SOFA
104** itself.
105**
106**
107** TERMS AND CONDITIONS
108**
109** Redistribution and use in source and binary forms, with or without
110** modification, are permitted provided that the following conditions
111** are met:
112**
113** 1 Redistributions of source code must retain the above copyright
114** notice, this list of conditions and the following disclaimer.
115**
116** 2 Redistributions in binary form must reproduce the above copyright
117** notice, this list of conditions and the following disclaimer in
118** the documentation and/or other materials provided with the
119** distribution.
120**
121** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
122** the International Astronomical Union nor the names of its
123** contributors may be used to endorse or promote products derived
124** from this software without specific prior written permission.
125**
126** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
127** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
128** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
129** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
130** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
131** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
132** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
133** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
134** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
135** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
136** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
137** POSSIBILITY OF SUCH DAMAGE.
138**
139*/
Note: See TracBrowser for help on using the repository browser.