1 #include "sofa.h"
2
iauEe00a(double date1,double date2)3 double iauEe00a(double date1, double date2)
4 /*
5 ** - - - - - - - - -
6 ** i a u E e 0 0 a
7 ** - - - - - - - - -
8 **
9 ** Equation of the equinoxes, compatible with IAU 2000 resolutions.
10 **
11 ** This function is part of the International Astronomical Union's
12 ** SOFA (Standards Of Fundamental Astronomy) software collection.
13 **
14 ** Status: support function.
15 **
16 ** Given:
17 ** date1,date2 double TT as a 2-part Julian Date (Note 1)
18 **
19 ** Returned (function value):
20 ** double equation of the equinoxes (Note 2)
21 **
22 ** Notes:
23 **
24 ** 1) The TT date date1+date2 is a Julian Date, apportioned in any
25 ** convenient way between the two arguments. For example,
26 ** JD(TT)=2450123.7 could be expressed in any of these ways,
27 ** among others:
28 **
29 ** date1 date2
30 **
31 ** 2450123.7 0.0 (JD method)
32 ** 2451545.0 -1421.3 (J2000 method)
33 ** 2400000.5 50123.2 (MJD method)
34 ** 2450123.5 0.2 (date & time method)
35 **
36 ** The JD method is the most natural and convenient to use in
37 ** cases where the loss of several decimal digits of resolution
38 ** is acceptable. The J2000 method is best matched to the way
39 ** the argument is handled internally and will deliver the
40 ** optimum resolution. The MJD method and the date & time methods
41 ** are both good compromises between resolution and convenience.
42 **
43 ** 2) The result, which is in radians, operates in the following sense:
44 **
45 ** Greenwich apparent ST = GMST + equation of the equinoxes
46 **
47 ** 3) The result is compatible with the IAU 2000 resolutions. For
48 ** further details, see IERS Conventions 2003 and Capitaine et al.
49 ** (2002).
50 **
51 ** Called:
52 ** iauPr00 IAU 2000 precession adjustments
53 ** iauObl80 mean obliquity, IAU 1980
54 ** iauNut00a nutation, IAU 2000A
55 ** iauEe00 equation of the equinoxes, IAU 2000
56 **
57 ** References:
58 **
59 ** Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
60 ** implement the IAU 2000 definition of UT1", Astronomy &
61 ** Astrophysics, 406, 1135-1149 (2003).
62 **
63 ** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
64 ** IERS Technical Note No. 32, BKG (2004).
65 **
66 ** This revision: 2021 May 11
67 **
68 ** SOFA release 2021-05-12
69 **
70 ** Copyright (C) 2021 IAU SOFA Board. See notes at end.
71 */
72 {
73 double dpsipr, depspr, epsa, dpsi, deps, ee;
74
75
76 /* IAU 2000 precession-rate adjustments. */
77 iauPr00(date1, date2, &dpsipr, &depspr);
78
79 /* Mean obliquity, consistent with IAU 2000 precession-nutation. */
80 epsa = iauObl80(date1, date2) + depspr;
81
82 /* Nutation in longitude. */
83 iauNut00a(date1, date2, &dpsi, &deps);
84
85 /* Equation of the equinoxes. */
86 ee = iauEe00(date1, date2, epsa, dpsi);
87
88 return ee;
89
90 /* Finished. */
91
92 /*----------------------------------------------------------------------
93 **
94 ** Copyright (C) 2021
95 ** Standards Of Fundamental Astronomy Board
96 ** of the International Astronomical Union.
97 **
98 ** =====================
99 ** SOFA Software License
100 ** =====================
101 **
102 ** NOTICE TO USER:
103 **
104 ** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
105 ** CONDITIONS WHICH APPLY TO ITS USE.
106 **
107 ** 1. The Software is owned by the IAU SOFA Board ("SOFA").
108 **
109 ** 2. Permission is granted to anyone to use the SOFA software for any
110 ** purpose, including commercial applications, free of charge and
111 ** without payment of royalties, subject to the conditions and
112 ** restrictions listed below.
113 **
114 ** 3. You (the user) may copy and distribute SOFA source code to others,
115 ** and use and adapt its code and algorithms in your own software,
116 ** on a world-wide, royalty-free basis. That portion of your
117 ** distribution that does not consist of intact and unchanged copies
118 ** of SOFA source code files is a "derived work" that must comply
119 ** with the following requirements:
120 **
121 ** a) Your work shall be marked or carry a statement that it
122 ** (i) uses routines and computations derived by you from
123 ** software provided by SOFA under license to you; and
124 ** (ii) does not itself constitute software provided by and/or
125 ** endorsed by SOFA.
126 **
127 ** b) The source code of your derived work must contain descriptions
128 ** of how the derived work is based upon, contains and/or differs
129 ** from the original SOFA software.
130 **
131 ** c) The names of all routines in your derived work shall not
132 ** include the prefix "iau" or "sofa" or trivial modifications
133 ** thereof such as changes of case.
134 **
135 ** d) The origin of the SOFA components of your derived work must
136 ** not be misrepresented; you must not claim that you wrote the
137 ** original software, nor file a patent application for SOFA
138 ** software or algorithms embedded in the SOFA software.
139 **
140 ** e) These requirements must be reproduced intact in any source
141 ** distribution and shall apply to anyone to whom you have
142 ** granted a further right to modify the source code of your
143 ** derived work.
144 **
145 ** Note that, as originally distributed, the SOFA software is
146 ** intended to be a definitive implementation of the IAU standards,
147 ** and consequently third-party modifications are discouraged. All
148 ** variations, no matter how minor, must be explicitly marked as
149 ** such, as explained above.
150 **
151 ** 4. You shall not cause the SOFA software to be brought into
152 ** disrepute, either by misuse, or use for inappropriate tasks, or
153 ** by inappropriate modification.
154 **
155 ** 5. The SOFA software is provided "as is" and SOFA makes no warranty
156 ** as to its use or performance. SOFA does not and cannot warrant
157 ** the performance or results which the user may obtain by using the
158 ** SOFA software. SOFA makes no warranties, express or implied, as
159 ** to non-infringement of third party rights, merchantability, or
160 ** fitness for any particular purpose. In no event will SOFA be
161 ** liable to the user for any consequential, incidental, or special
162 ** damages, including any lost profits or lost savings, even if a
163 ** SOFA representative has been advised of such damages, or for any
164 ** claim by any third party.
165 **
166 ** 6. The provision of any version of the SOFA software under the terms
167 ** and conditions specified herein does not imply that future
168 ** versions will also be made available under the same terms and
169 ** conditions.
170 *
171 ** In any published work or commercial product which uses the SOFA
172 ** software directly, acknowledgement (see www.iausofa.org) is
173 ** appreciated.
174 **
175 ** Correspondence concerning SOFA software should be addressed as
176 ** follows:
177 **
178 ** By email: sofa@ukho.gov.uk
179 ** By post: IAU SOFA Center
180 ** HM Nautical Almanac Office
181 ** UK Hydrographic Office
182 ** Admiralty Way, Taunton
183 ** Somerset, TA1 2DN
184 ** United Kingdom
185 **
186 **--------------------------------------------------------------------*/
187 }
188