source: trunk/FACT++/sofa/src/gst00b.c@ 18346

Last change on this file since 18346 was 18346, checked in by tbretz, 9 years ago
File size: 7.6 KB
Line 
1#include "sofa.h"
2
3double iauGst00b(double uta, double utb)
4/*
5** - - - - - - - - - -
6** i a u 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** This function is part of the International Astronomical Union's
13** SOFA (Standards Of Fundamental Astronomy) software collection.
14**
15** Status: support function.
16**
17** Given:
18** uta,utb double UT1 as a 2-part Julian Date (Notes 1,2)
19**
20** Returned (function value):
21** double Greenwich apparent sidereal time (radians)
22**
23** Notes:
24**
25** 1) The UT1 date uta+utb is a Julian Date, apportioned in any
26** convenient way between the argument pair. For example,
27** JD=2450123.7 could be expressed in any of these ways, among
28** others:
29**
30** uta utb
31**
32** 2450123.7 0.0 (JD method)
33** 2451545.0 -1421.3 (J2000 method)
34** 2400000.5 50123.2 (MJD method)
35** 2450123.5 0.2 (date & time method)
36**
37** The JD method is the most natural and convenient to use in cases
38** where the loss of several decimal digits of resolution is
39** acceptable. The J2000 and MJD methods are good compromises
40** between resolution and convenience. For UT, the date & time
41** method is best matched to the algorithm that is used by the Earth
42** Rotation Angle function, called internally: maximum precision is
43** delivered when the uta argument is for 0hrs UT1 on the day in
44** question and the utb argument lies in the range 0 to 1, or vice
45** versa.
46**
47** 2) The result is compatible with the IAU 2000 resolutions, except
48** that accuracy has been compromised for the sake of speed and
49** convenience in two respects:
50**
51** . UT is used instead of TDB (or TT) to compute the precession
52** component of GMST and the equation of the equinoxes. This
53** results in errors of order 0.1 mas at present.
54**
55** . The IAU 2000B abridged nutation model (McCarthy & Luzum, 2001)
56** is used, introducing errors of up to 1 mas.
57**
58** 3) This GAST is compatible with the IAU 2000 resolutions and must be
59** used only in conjunction with other IAU 2000 compatible
60** components such as precession-nutation.
61**
62** 4) The result is returned in the range 0 to 2pi.
63**
64** 5) The algorithm is from Capitaine et al. (2003) and IERS
65** Conventions 2003.
66**
67** Called:
68** iauGmst00 Greenwich mean sidereal time, IAU 2000
69** iauEe00b equation of the equinoxes, IAU 2000B
70** iauAnp normalize angle into range 0 to 2pi
71**
72** References:
73**
74** Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
75** implement the IAU 2000 definition of UT1", Astronomy &
76** Astrophysics, 406, 1135-1149 (2003)
77**
78** McCarthy, D.D. & Luzum, B.J., "An abridged model of the
79** precession-nutation of the celestial pole", Celestial Mechanics &
80** Dynamical Astronomy, 85, 37-49 (2003)
81**
82** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
83** IERS Technical Note No. 32, BKG (2004)
84**
85** This revision: 2013 June 18
86**
87** SOFA release 2015-02-09
88**
89** Copyright (C) 2015 IAU SOFA Board. See notes at end.
90*/
91{
92 double gmst00, ee00b, gst;
93
94 gmst00 = iauGmst00(uta, utb, uta, utb);
95 ee00b = iauEe00b(uta, utb);
96 gst = iauAnp(gmst00 + ee00b);
97
98 return gst;
99
100/*----------------------------------------------------------------------
101**
102** Copyright (C) 2015
103** Standards Of Fundamental Astronomy Board
104** of the International Astronomical Union.
105**
106** =====================
107** SOFA Software License
108** =====================
109**
110** NOTICE TO USER:
111**
112** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
113** CONDITIONS WHICH APPLY TO ITS USE.
114**
115** 1. The Software is owned by the IAU SOFA Board ("SOFA").
116**
117** 2. Permission is granted to anyone to use the SOFA software for any
118** purpose, including commercial applications, free of charge and
119** without payment of royalties, subject to the conditions and
120** restrictions listed below.
121**
122** 3. You (the user) may copy and distribute SOFA source code to others,
123** and use and adapt its code and algorithms in your own software,
124** on a world-wide, royalty-free basis. That portion of your
125** distribution that does not consist of intact and unchanged copies
126** of SOFA source code files is a "derived work" that must comply
127** with the following requirements:
128**
129** a) Your work shall be marked or carry a statement that it
130** (i) uses routines and computations derived by you from
131** software provided by SOFA under license to you; and
132** (ii) does not itself constitute software provided by and/or
133** endorsed by SOFA.
134**
135** b) The source code of your derived work must contain descriptions
136** of how the derived work is based upon, contains and/or differs
137** from the original SOFA software.
138**
139** c) The names of all routines in your derived work shall not
140** include the prefix "iau" or "sofa" or trivial modifications
141** thereof such as changes of case.
142**
143** d) The origin of the SOFA components of your derived work must
144** not be misrepresented; you must not claim that you wrote the
145** original software, nor file a patent application for SOFA
146** software or algorithms embedded in the SOFA software.
147**
148** e) These requirements must be reproduced intact in any source
149** distribution and shall apply to anyone to whom you have
150** granted a further right to modify the source code of your
151** derived work.
152**
153** Note that, as originally distributed, the SOFA software is
154** intended to be a definitive implementation of the IAU standards,
155** and consequently third-party modifications are discouraged. All
156** variations, no matter how minor, must be explicitly marked as
157** such, as explained above.
158**
159** 4. You shall not cause the SOFA software to be brought into
160** disrepute, either by misuse, or use for inappropriate tasks, or
161** by inappropriate modification.
162**
163** 5. The SOFA software is provided "as is" and SOFA makes no warranty
164** as to its use or performance. SOFA does not and cannot warrant
165** the performance or results which the user may obtain by using the
166** SOFA software. SOFA makes no warranties, express or implied, as
167** to non-infringement of third party rights, merchantability, or
168** fitness for any particular purpose. In no event will SOFA be
169** liable to the user for any consequential, incidental, or special
170** damages, including any lost profits or lost savings, even if a
171** SOFA representative has been advised of such damages, or for any
172** claim by any third party.
173**
174** 6. The provision of any version of the SOFA software under the terms
175** and conditions specified herein does not imply that future
176** versions will also be made available under the same terms and
177** conditions.
178*
179** In any published work or commercial product which uses the SOFA
180** software directly, acknowledgement (see www.iausofa.org) is
181** appreciated.
182**
183** Correspondence concerning SOFA software should be addressed as
184** follows:
185**
186** By email: sofa@ukho.gov.uk
187** By post: IAU SOFA Center
188** HM Nautical Almanac Office
189** UK Hydrographic Office
190** Admiralty Way, Taunton
191** Somerset, TA1 2DN
192** United Kingdom
193**
194**--------------------------------------------------------------------*/
195}
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