source: trunk/FACT++/erfa/src/gst00b.c@ 19594

Last change on this file since 19594 was 18921, checked in by tbretz, 8 years ago
Updated to ERFA 1.4.0
File size: 6.2 KB
Line 
1#include "erfa.h"
2
3double eraGst00b(double uta, double utb)
4/*
5** - - - - - - - - - -
6** e r a G s t 0 0 b
7** - - - - - - - - - -
8**
9** Greenwich apparent sidereal time (consistent with IAU 2000
10** resolutions but using the truncated nutation model IAU 2000B).
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 2000 resolutions, except
43** that accuracy has been compromised for the sake of speed and
44** convenience in two respects:
45**
46** . UT is used instead of TDB (or TT) to compute the precession
47** component of GMST and the equation of the equinoxes. This
48** results in errors of order 0.1 mas at present.
49**
50** . The IAU 2000B abridged nutation model (McCarthy & Luzum, 2001)
51** is used, introducing errors of up to 1 mas.
52**
53** 3) This GAST is compatible with the IAU 2000 resolutions and must be
54** used only in conjunction with other IAU 2000 compatible
55** components such as precession-nutation.
56**
57** 4) The result is returned in the range 0 to 2pi.
58**
59** 5) The algorithm is from Capitaine et al. (2003) and IERS
60** Conventions 2003.
61**
62** Called:
63** eraGmst00 Greenwich mean sidereal time, IAU 2000
64** eraEe00b equation of the equinoxes, IAU 2000B
65** eraAnp normalize angle into range 0 to 2pi
66**
67** References:
68**
69** Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
70** implement the IAU 2000 definition of UT1", Astronomy &
71** Astrophysics, 406, 1135-1149 (2003)
72**
73** McCarthy, D.D. & Luzum, B.J., "An abridged model of the
74** precession-nutation of the celestial pole", Celestial Mechanics &
75** Dynamical Astronomy, 85, 37-49 (2003)
76**
77** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
78** IERS Technical Note No. 32, BKG (2004)
79**
80** Copyright (C) 2013-2017, NumFOCUS Foundation.
81** Derived, with permission, from the SOFA library. See notes at end of file.
82*/
83{
84 double gmst00, ee00b, gst;
85
86
87 gmst00 = eraGmst00(uta, utb, uta, utb);
88 ee00b = eraEe00b(uta, utb);
89 gst = eraAnp(gmst00 + ee00b);
90
91 return gst;
92
93}
94/*----------------------------------------------------------------------
95**
96**
97** Copyright (C) 2013-2017, NumFOCUS Foundation.
98** All rights reserved.
99**
100** This library is derived, with permission, from the International
101** Astronomical Union's "Standards of Fundamental Astronomy" library,
102** available from http://www.iausofa.org.
103**
104** The ERFA version is intended to retain identical functionality to
105** the SOFA library, but made distinct through different function and
106** file names, as set out in the SOFA license conditions. The SOFA
107** original has a role as a reference standard for the IAU and IERS,
108** and consequently redistribution is permitted only in its unaltered
109** state. The ERFA version is not subject to this restriction and
110** therefore can be included in distributions which do not support the
111** concept of "read only" software.
112**
113** Although the intent is to replicate the SOFA API (other than
114** replacement of prefix names) and results (with the exception of
115** bugs; any that are discovered will be fixed), SOFA is not
116** responsible for any errors found in this version of the library.
117**
118** If you wish to acknowledge the SOFA heritage, please acknowledge
119** that you are using a library derived from SOFA, rather than SOFA
120** itself.
121**
122**
123** TERMS AND CONDITIONS
124**
125** Redistribution and use in source and binary forms, with or without
126** modification, are permitted provided that the following conditions
127** are met:
128**
129** 1 Redistributions of source code must retain the above copyright
130** notice, this list of conditions and the following disclaimer.
131**
132** 2 Redistributions in binary form must reproduce the above copyright
133** notice, this list of conditions and the following disclaimer in
134** the documentation and/or other materials provided with the
135** distribution.
136**
137** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
138** the International Astronomical Union nor the names of its
139** contributors may be used to endorse or promote products derived
140** from this software without specific prior written permission.
141**
142** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
143** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
144** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
145** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
146** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
147** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
148** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
149** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
150** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
151** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
152** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
153** POSSIBILITY OF SUCH DAMAGE.
154**
155*/
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