source: trunk/FACT++/erfa/src/gst00a.c@ 18711

Last change on this file since 18711 was 18711, checked in by tbretz, 9 years ago
Updated to ERFA 1.3.0 (no relevant code change except the leap second at the beginning of 2017)
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) 2013-2016, 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
79 gmst00 = eraGmst00(uta, utb, tta, ttb);
80 ee00a = eraEe00a(tta, ttb);
81 gst = eraAnp(gmst00 + ee00a);
82
83 return gst;
84
85}
86/*----------------------------------------------------------------------
87**
88**
89** Copyright (C) 2013-2016, NumFOCUS Foundation.
90** All rights reserved.
91**
92** This library is derived, with permission, from the International
93** Astronomical Union's "Standards of Fundamental Astronomy" library,
94** available from http://www.iausofa.org.
95**
96** The ERFA version is intended to retain identical functionality to
97** the SOFA library, but made distinct through different function and
98** file names, as set out in the SOFA license conditions. The SOFA
99** original has a role as a reference standard for the IAU and IERS,
100** and consequently redistribution is permitted only in its unaltered
101** state. The ERFA version is not subject to this restriction and
102** therefore can be included in distributions which do not support the
103** concept of "read only" software.
104**
105** Although the intent is to replicate the SOFA API (other than
106** replacement of prefix names) and results (with the exception of
107** bugs; any that are discovered will be fixed), SOFA is not
108** responsible for any errors found in this version of the library.
109**
110** If you wish to acknowledge the SOFA heritage, please acknowledge
111** that you are using a library derived from SOFA, rather than SOFA
112** itself.
113**
114**
115** TERMS AND CONDITIONS
116**
117** Redistribution and use in source and binary forms, with or without
118** modification, are permitted provided that the following conditions
119** are met:
120**
121** 1 Redistributions of source code must retain the above copyright
122** notice, this list of conditions and the following disclaimer.
123**
124** 2 Redistributions in binary form must reproduce the above copyright
125** notice, this list of conditions and the following disclaimer in
126** the documentation and/or other materials provided with the
127** distribution.
128**
129** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
130** the International Astronomical Union nor the names of its
131** contributors may be used to endorse or promote products derived
132** from this software without specific prior written permission.
133**
134** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
135** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
136** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
137** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
138** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
139** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
140** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
141** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
142** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
143** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
144** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
145** POSSIBILITY OF SUCH DAMAGE.
146**
147*/
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