source: trunk/FACT++/erfa/src/gst00a.c@ 18679

Last change on this file since 18679 was 18348, checked in by tbretz, 9 years ago
File size: 5.9 KB
Line 
1#include "erfa.h"
2
3double eraGst00a(double uta, double utb, double tta, double ttb)
4/*
5** - - - - - - - - - -
6** e r a G s t 0 0 a
7** - - - - - - - - - -
8**
9** Greenwich apparent sidereal time (consistent with IAU 2000
10** resolutions).
11**
12** Given:
13** uta,utb double UT1 as a 2-part Julian Date (Notes 1,2)
14** tta,ttb double TT as a 2-part Julian Date (Notes 1,2)
15**
16** Returned (function value):
17** double Greenwich apparent sidereal time (radians)
18**
19** Notes:
20**
21** 1) The UT1 and TT dates uta+utb and tta+ttb respectively, are both
22** Julian Dates, apportioned in any convenient way between the
23** argument pairs. For example, JD=2450123.7 could be expressed in
24** any of these ways, among others:
25**
26** Part A Part B
27**
28** 2450123.7 0.0 (JD method)
29** 2451545.0 -1421.3 (J2000 method)
30** 2400000.5 50123.2 (MJD method)
31** 2450123.5 0.2 (date & time method)
32**
33** The JD method is the most natural and convenient to use in
34** cases where the loss of several decimal digits of resolution
35** is acceptable (in the case of UT; the TT is not at all critical
36** in this respect). The J2000 and MJD methods are good compromises
37** between resolution and convenience. For UT, the date & time
38** method is best matched to the algorithm that is used by the Earth
39** Rotation Angle function, called internally: maximum precision is
40** delivered when the uta argument is for 0hrs UT1 on the day in
41** question and the utb argument lies in the range 0 to 1, or vice
42** versa.
43**
44** 2) Both UT1 and TT are required, UT1 to predict the Earth rotation
45** and TT to predict the effects of precession-nutation. If UT1 is
46** used for both purposes, errors of order 100 microarcseconds
47** result.
48**
49** 3) This GAST is compatible with the IAU 2000 resolutions and must be
50** used only in conjunction with other IAU 2000 compatible
51** components such as precession-nutation.
52**
53** 4) The result is returned in the range 0 to 2pi.
54**
55** 5) The algorithm is from Capitaine et al. (2003) and IERS
56** Conventions 2003.
57**
58** Called:
59** eraGmst00 Greenwich mean sidereal time, IAU 2000
60** eraEe00a equation of the equinoxes, IAU 2000A
61** eraAnp normalize angle into range 0 to 2pi
62**
63** References:
64**
65** Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
66** implement the IAU 2000 definition of UT1", Astronomy &
67** Astrophysics, 406, 1135-1149 (2003)
68**
69** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
70** IERS Technical Note No. 32, BKG (2004)
71**
72** Copyright (C) 2013-2015, NumFOCUS Foundation.
73** Derived, with permission, from the SOFA library. See notes at end of file.
74*/
75{
76 double gmst00, ee00a, gst;
77
78 gmst00 = eraGmst00(uta, utb, tta, ttb);
79 ee00a = eraEe00a(tta, ttb);
80 gst = eraAnp(gmst00 + ee00a);
81
82 return gst;
83
84}
85/*----------------------------------------------------------------------
86**
87**
88** Copyright (C) 2013-2015, NumFOCUS Foundation.
89** All rights reserved.
90**
91** This library is derived, with permission, from the International
92** Astronomical Union's "Standards of Fundamental Astronomy" library,
93** available from http://www.iausofa.org.
94**
95** The ERFA version is intended to retain identical functionality to
96** the SOFA library, but made distinct through different function and
97** file names, as set out in the SOFA license conditions. The SOFA
98** original has a role as a reference standard for the IAU and IERS,
99** and consequently redistribution is permitted only in its unaltered
100** state. The ERFA version is not subject to this restriction and
101** therefore can be included in distributions which do not support the
102** concept of "read only" software.
103**
104** Although the intent is to replicate the SOFA API (other than
105** replacement of prefix names) and results (with the exception of
106** bugs; any that are discovered will be fixed), SOFA is not
107** responsible for any errors found in this version of the library.
108**
109** If you wish to acknowledge the SOFA heritage, please acknowledge
110** that you are using a library derived from SOFA, rather than SOFA
111** itself.
112**
113**
114** TERMS AND CONDITIONS
115**
116** Redistribution and use in source and binary forms, with or without
117** modification, are permitted provided that the following conditions
118** are met:
119**
120** 1 Redistributions of source code must retain the above copyright
121** notice, this list of conditions and the following disclaimer.
122**
123** 2 Redistributions in binary form must reproduce the above copyright
124** notice, this list of conditions and the following disclaimer in
125** the documentation and/or other materials provided with the
126** distribution.
127**
128** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
129** the International Astronomical Union nor the names of its
130** contributors may be used to endorse or promote products derived
131** from this software without specific prior written permission.
132**
133** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
134** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
135** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
136** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
137** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
138** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
139** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
140** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
141** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
142** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
143** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
144** POSSIBILITY OF SUCH DAMAGE.
145**
146*/
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