source: trunk/FACT++/erfa/src/eqeq94.c@ 20000

Last change on this file since 20000 was 18921, checked in by tbretz, 8 years ago
Updated to ERFA 1.4.0
File size: 5.4 KB
Line 
1#include "erfa.h"
2
3double eraEqeq94(double date1, double date2)
4/*
5** - - - - - - - - - -
6** e r a E q e q 9 4
7** - - - - - - - - - -
8**
9** Equation of the equinoxes, IAU 1994 model.
10**
11** Given:
12** date1,date2 double TDB date (Note 1)
13**
14** Returned (function value):
15** double equation of the equinoxes (Note 2)
16**
17** Notes:
18**
19** 1) The date date1+date2 is a Julian Date, apportioned in any
20** convenient way between the two arguments. For example,
21** JD(TT)=2450123.7 could be expressed in any of these ways,
22** among others:
23**
24** date1 date2
25**
26** 2450123.7 0.0 (JD method)
27** 2451545.0 -1421.3 (J2000 method)
28** 2400000.5 50123.2 (MJD method)
29** 2450123.5 0.2 (date & time method)
30**
31** The JD method is the most natural and convenient to use in
32** cases where the loss of several decimal digits of resolution
33** is acceptable. The J2000 method is best matched to the way
34** the argument is handled internally and will deliver the
35** optimum resolution. The MJD method and the date & time methods
36** are both good compromises between resolution and convenience.
37**
38** 2) The result, which is in radians, operates in the following sense:
39**
40** Greenwich apparent ST = GMST + equation of the equinoxes
41**
42** Called:
43** eraAnpm normalize angle into range +/- pi
44** eraNut80 nutation, IAU 1980
45** eraObl80 mean obliquity, IAU 1980
46**
47** References:
48**
49** IAU Resolution C7, Recommendation 3 (1994).
50**
51** Capitaine, N. & Gontier, A.-M., 1993, Astron. Astrophys., 275,
52** 645-650.
53**
54** Copyright (C) 2013-2017, NumFOCUS Foundation.
55** Derived, with permission, from the SOFA library. See notes at end of file.
56*/
57{
58 double t, om, dpsi, deps, eps0, ee;
59
60
61/* Interval between fundamental epoch J2000.0 and given date (JC). */
62 t = ((date1 - ERFA_DJ00) + date2) / ERFA_DJC;
63
64/* Longitude of the mean ascending node of the lunar orbit on the */
65/* ecliptic, measured from the mean equinox of date. */
66 om = eraAnpm((450160.280 + (-482890.539
67 + (7.455 + 0.008 * t) * t) * t) * ERFA_DAS2R
68 + fmod(-5.0 * t, 1.0) * ERFA_D2PI);
69
70/* Nutation components and mean obliquity. */
71 eraNut80(date1, date2, &dpsi, &deps);
72 eps0 = eraObl80(date1, date2);
73
74/* Equation of the equinoxes. */
75 ee = dpsi*cos(eps0) + ERFA_DAS2R*(0.00264*sin(om) + 0.000063*sin(om+om));
76
77 return ee;
78
79}
80/*----------------------------------------------------------------------
81**
82**
83** Copyright (C) 2013-2017, NumFOCUS Foundation.
84** All rights reserved.
85**
86** This library is derived, with permission, from the International
87** Astronomical Union's "Standards of Fundamental Astronomy" library,
88** available from http://www.iausofa.org.
89**
90** The ERFA version is intended to retain identical functionality to
91** the SOFA library, but made distinct through different function and
92** file names, as set out in the SOFA license conditions. The SOFA
93** original has a role as a reference standard for the IAU and IERS,
94** and consequently redistribution is permitted only in its unaltered
95** state. The ERFA version is not subject to this restriction and
96** therefore can be included in distributions which do not support the
97** concept of "read only" software.
98**
99** Although the intent is to replicate the SOFA API (other than
100** replacement of prefix names) and results (with the exception of
101** bugs; any that are discovered will be fixed), SOFA is not
102** responsible for any errors found in this version of the library.
103**
104** If you wish to acknowledge the SOFA heritage, please acknowledge
105** that you are using a library derived from SOFA, rather than SOFA
106** itself.
107**
108**
109** TERMS AND CONDITIONS
110**
111** Redistribution and use in source and binary forms, with or without
112** modification, are permitted provided that the following conditions
113** are met:
114**
115** 1 Redistributions of source code must retain the above copyright
116** notice, this list of conditions and the following disclaimer.
117**
118** 2 Redistributions in binary form must reproduce the above copyright
119** notice, this list of conditions and the following disclaimer in
120** the documentation and/or other materials provided with the
121** distribution.
122**
123** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
124** the International Astronomical Union nor the names of its
125** contributors may be used to endorse or promote products derived
126** from this software without specific prior written permission.
127**
128** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
129** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
130** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
131** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
132** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
133** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
134** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
135** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
136** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
137** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
138** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
139** POSSIBILITY OF SUCH DAMAGE.
140**
141*/
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