source: branches/FACT++_part_filenames/erfa/src/gmst06.c

Last change on this file was 18711, checked in by tbretz, 8 years ago
Updated to ERFA 1.3.0 (no relevant code change except the leap second at the beginning of 2017)
File size: 5.8 KB
Line 
1#include "erfa.h"
2
3double eraGmst06(double uta, double utb, double tta, double ttb)
4/*
5** - - - - - - - - - -
6** e r a G m s t 0 6
7** - - - - - - - - - -
8**
9** Greenwich mean sidereal time (consistent with IAU 2006 precession).
10**
11** Given:
12** uta,utb double UT1 as a 2-part Julian Date (Notes 1,2)
13** tta,ttb double TT as a 2-part Julian Date (Notes 1,2)
14**
15** Returned (function value):
16** double Greenwich mean sidereal time (radians)
17**
18** Notes:
19**
20** 1) The UT1 and TT dates uta+utb and tta+ttb respectively, are both
21** Julian Dates, apportioned in any convenient way between the
22** argument pairs. For example, JD=2450123.7 could be expressed in
23** any of these ways, among others:
24**
25** Part A Part B
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
33** cases where the loss of several decimal digits of resolution
34** is acceptable (in the case of UT; the TT is not at all critical
35** in this respect). The J2000 and MJD methods are good compromises
36** between resolution and convenience. For UT, the date & time
37** method is best matched to the algorithm that is used by the Earth
38** rotation angle function, called internally: maximum precision is
39** delivered when the uta argument is for 0hrs UT1 on the day in
40** question and the utb argument lies in the range 0 to 1, or vice
41** versa.
42**
43** 2) Both UT1 and TT are required, UT1 to predict the Earth rotation
44** and TT to predict the effects of precession. If UT1 is used for
45** both purposes, errors of order 100 microarcseconds result.
46**
47** 3) This GMST is compatible with the IAU 2006 precession and must not
48** be used with other precession models.
49**
50** 4) The result is returned in the range 0 to 2pi.
51**
52** Called:
53** eraEra00 Earth rotation angle, IAU 2000
54** eraAnp normalize angle into range 0 to 2pi
55**
56** Reference:
57**
58** Capitaine, N., Wallace, P.T. & Chapront, J., 2005,
59** Astron.Astrophys. 432, 355
60**
61** Copyright (C) 2013-2016, NumFOCUS Foundation.
62** Derived, with permission, from the SOFA library. See notes at end of file.
63*/
64{
65 double t, gmst;
66
67
68/* TT Julian centuries since J2000.0. */
69 t = ((tta - ERFA_DJ00) + ttb) / ERFA_DJC;
70
71/* Greenwich mean sidereal time, IAU 2006. */
72 gmst = eraAnp(eraEra00(uta, utb) +
73 ( 0.014506 +
74 ( 4612.156534 +
75 ( 1.3915817 +
76 ( -0.00000044 +
77 ( -0.000029956 +
78 ( -0.0000000368 )
79 * t) * t) * t) * t) * t) * ERFA_DAS2R);
80
81 return gmst;
82
83}
84/*----------------------------------------------------------------------
85**
86**
87** Copyright (C) 2013-2016, NumFOCUS Foundation.
88** All rights reserved.
89**
90** This library is derived, with permission, from the International
91** Astronomical Union's "Standards of Fundamental Astronomy" library,
92** available from http://www.iausofa.org.
93**
94** The ERFA version is intended to retain identical functionality to
95** the SOFA library, but made distinct through different function and
96** file names, as set out in the SOFA license conditions. The SOFA
97** original has a role as a reference standard for the IAU and IERS,
98** and consequently redistribution is permitted only in its unaltered
99** state. The ERFA version is not subject to this restriction and
100** therefore can be included in distributions which do not support the
101** concept of "read only" software.
102**
103** Although the intent is to replicate the SOFA API (other than
104** replacement of prefix names) and results (with the exception of
105** bugs; any that are discovered will be fixed), SOFA is not
106** responsible for any errors found in this version of the library.
107**
108** If you wish to acknowledge the SOFA heritage, please acknowledge
109** that you are using a library derived from SOFA, rather than SOFA
110** itself.
111**
112**
113** TERMS AND CONDITIONS
114**
115** Redistribution and use in source and binary forms, with or without
116** modification, are permitted provided that the following conditions
117** are met:
118**
119** 1 Redistributions of source code must retain the above copyright
120** notice, this list of conditions and the following disclaimer.
121**
122** 2 Redistributions in binary form must reproduce the above copyright
123** notice, this list of conditions and the following disclaimer in
124** the documentation and/or other materials provided with the
125** distribution.
126**
127** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
128** the International Astronomical Union nor the names of its
129** contributors may be used to endorse or promote products derived
130** from this software without specific prior written permission.
131**
132** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
133** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
134** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
135** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
136** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
137** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
138** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
139** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
140** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
141** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
142** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
143** POSSIBILITY OF SUCH DAMAGE.
144**
145*/
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