1 #include "erfa.h"
2
eraEe00a(double date1,double date2)3 double eraEe00a(double date1, double date2)
4 /*
5 ** - - - - - - - - -
6 ** e r a E e 0 0 a
7 ** - - - - - - - - -
8 **
9 ** Equation of the equinoxes, compatible with IAU 2000 resolutions.
10 **
11 ** Given:
12 ** date1,date2 double TT as a 2-part Julian Date (Note 1)
13 **
14 ** Returned (function value):
15 ** double equation of the equinoxes (Note 2)
16 **
17 ** Notes:
18 **
19 ** 1) The TT 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 ** 3) The result is compatible with the IAU 2000 resolutions. For
43 ** further details, see IERS Conventions 2003 and Capitaine et al.
44 ** (2002).
45 **
46 ** Called:
47 ** eraPr00 IAU 2000 precession adjustments
48 ** eraObl80 mean obliquity, IAU 1980
49 ** eraNut00a nutation, IAU 2000A
50 ** eraEe00 equation of the equinoxes, IAU 2000
51 **
52 ** References:
53 **
54 ** Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
55 ** implement the IAU 2000 definition of UT1", Astronomy &
56 ** Astrophysics, 406, 1135-1149 (2003).
57 **
58 ** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
59 ** IERS Technical Note No. 32, BKG (2004).
60 **
61 ** This revision: 2021 May 11
62 **
63 ** Copyright (C) 2013-2021, NumFOCUS Foundation.
64 ** Derived, with permission, from the SOFA library. See notes at end of file.
65 */
66 {
67 double dpsipr, depspr, epsa, dpsi, deps, ee;
68
69
70 /* IAU 2000 precession-rate adjustments. */
71 eraPr00(date1, date2, &dpsipr, &depspr);
72
73 /* Mean obliquity, consistent with IAU 2000 precession-nutation. */
74 epsa = eraObl80(date1, date2) + depspr;
75
76 /* Nutation in longitude. */
77 eraNut00a(date1, date2, &dpsi, &deps);
78
79 /* Equation of the equinoxes. */
80 ee = eraEe00(date1, date2, epsa, dpsi);
81
82 return ee;
83
84 /* Finished. */
85
86 }
87 /*----------------------------------------------------------------------
88 **
89 **
90 ** Copyright (C) 2013-2021, NumFOCUS Foundation.
91 ** All rights reserved.
92 **
93 ** This library is derived, with permission, from the International
94 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
95 ** available from http://www.iausofa.org.
96 **
97 ** The ERFA version is intended to retain identical functionality to
98 ** the SOFA library, but made distinct through different function and
99 ** file names, as set out in the SOFA license conditions. The SOFA
100 ** original has a role as a reference standard for the IAU and IERS,
101 ** and consequently redistribution is permitted only in its unaltered
102 ** state. The ERFA version is not subject to this restriction and
103 ** therefore can be included in distributions which do not support the
104 ** concept of "read only" software.
105 **
106 ** Although the intent is to replicate the SOFA API (other than
107 ** replacement of prefix names) and results (with the exception of
108 ** bugs; any that are discovered will be fixed), SOFA is not
109 ** responsible for any errors found in this version of the library.
110 **
111 ** If you wish to acknowledge the SOFA heritage, please acknowledge
112 ** that you are using a library derived from SOFA, rather than SOFA
113 ** itself.
114 **
115 **
116 ** TERMS AND CONDITIONS
117 **
118 ** Redistribution and use in source and binary forms, with or without
119 ** modification, are permitted provided that the following conditions
120 ** are met:
121 **
122 ** 1 Redistributions of source code must retain the above copyright
123 ** notice, this list of conditions and the following disclaimer.
124 **
125 ** 2 Redistributions in binary form must reproduce the above copyright
126 ** notice, this list of conditions and the following disclaimer in
127 ** the documentation and/or other materials provided with the
128 ** distribution.
129 **
130 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
131 ** the International Astronomical Union nor the names of its
132 ** contributors may be used to endorse or promote products derived
133 ** from this software without specific prior written permission.
134 **
135 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
136 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
137 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
138 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
139 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
140 ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
141 ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
142 ** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
143 ** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
144 ** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
145 ** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
146 ** POSSIBILITY OF SUCH DAMAGE.
147 **
148 */
149