FACT++  1.0
gmst00.c
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1 #include "erfa.h"
2 
3 double eraGmst00(double uta, double utb, double tta, double ttb)
4 /*
5 ** - - - - - - - - - -
6 ** e r a G m s t 0 0
7 ** - - - - - - - - - -
8 **
9 ** Greenwich mean sidereal time (model 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 mean 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. If UT1 is used for
46 ** both purposes, errors of order 100 microarcseconds result.
47 **
48 ** 3) This GMST is compatible with the IAU 2000 resolutions and must be
49 ** used only in conjunction with other IAU 2000 compatible
50 ** components such as precession-nutation and equation of the
51 ** equinoxes.
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 ** eraEra00 Earth rotation angle, IAU 2000
60 ** eraAnp normalize angle into range 0 to 2pi
61 **
62 ** References:
63 **
64 ** Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
65 ** implement the IAU 2000 definition of UT1", Astronomy &
66 ** Astrophysics, 406, 1135-1149 (2003)
67 **
68 ** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
69 ** IERS Technical Note No. 32, BKG (2004)
70 **
71 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
72 ** Derived, with permission, from the SOFA library. See notes at end of file.
73 */
74 {
75  double t, gmst;
76 
77 /* TT Julian centuries since J2000.0. */
78  t = ((tta - ERFA_DJ00) + ttb) / ERFA_DJC;
79 
80 /* Greenwich Mean Sidereal Time, IAU 2000. */
81  gmst = eraAnp(eraEra00(uta, utb) +
82  ( 0.014506 +
83  ( 4612.15739966 +
84  ( 1.39667721 +
85  ( -0.00009344 +
86  ( 0.00001882 )
87  * t) * t) * t) * t) * ERFA_DAS2R);
88 
89  return gmst;
90 
91 }
92 /*----------------------------------------------------------------------
93 **
94 **
95 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
96 ** All rights reserved.
97 **
98 ** This library is derived, with permission, from the International
99 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
100 ** available from http://www.iausofa.org.
101 **
102 ** The ERFA version is intended to retain identical functionality to
103 ** the SOFA library, but made distinct through different function and
104 ** file names, as set out in the SOFA license conditions. The SOFA
105 ** original has a role as a reference standard for the IAU and IERS,
106 ** and consequently redistribution is permitted only in its unaltered
107 ** state. The ERFA version is not subject to this restriction and
108 ** therefore can be included in distributions which do not support the
109 ** concept of "read only" software.
110 **
111 ** Although the intent is to replicate the SOFA API (other than
112 ** replacement of prefix names) and results (with the exception of
113 ** bugs; any that are discovered will be fixed), SOFA is not
114 ** responsible for any errors found in this version of the library.
115 **
116 ** If you wish to acknowledge the SOFA heritage, please acknowledge
117 ** that you are using a library derived from SOFA, rather than SOFA
118 ** itself.
119 **
120 **
121 ** TERMS AND CONDITIONS
122 **
123 ** Redistribution and use in source and binary forms, with or without
124 ** modification, are permitted provided that the following conditions
125 ** are met:
126 **
127 ** 1 Redistributions of source code must retain the above copyright
128 ** notice, this list of conditions and the following disclaimer.
129 **
130 ** 2 Redistributions in binary form must reproduce the above copyright
131 ** notice, this list of conditions and the following disclaimer in
132 ** the documentation and/or other materials provided with the
133 ** distribution.
134 **
135 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
136 ** the International Astronomical Union nor the names of its
137 ** contributors may be used to endorse or promote products derived
138 ** from this software without specific prior written permission.
139 **
140 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
141 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
142 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
143 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
144 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
145 ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
146 ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
147 ** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
148 ** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
149 ** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
150 ** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
151 ** POSSIBILITY OF SUCH DAMAGE.
152 **
153 */
ERFA_DJ00
#define ERFA_DJ00
Definition: erfam.h:87
ERFA_DAS2R
#define ERFA_DAS2R
Definition: erfam.h:60
eraEra00
double eraEra00(double dj1, double dj2)
Definition: era00.c:3
ERFA_DJC
#define ERFA_DJC
Definition: erfam.h:81
t
TT t
Definition: test_client.c:26
eraAnp
double eraAnp(double a)
Definition: anp.c:3
eraGmst00
double eraGmst00(double uta, double utb, double tta, double ttb)
Definition: gmst00.c:3