1 /*
2 * - - - - - - - - - -
3 * g a l _ e e 0 0 a
4 * - - - - - - - - - -
5 *
6 * This routine is part of the General Astrodynamics Library
7 *
8 * Description:
9 *
10 * Equation of the equinoxes, compatible with IAU 2000 resolutions.
11 *
12 * This routine is an independent translation of a FORTRAN routine
13 * that is part of IAU's SOFA software collection.
14 *
15 * Status:
16 *
17 * support routine.
18 *
19 * Given:
20 *
21 * date1,date2 d TT as a 2-part Julian Date (Note 1)
22 *
23 * Returned:
24 *
25 * gal_ee00a d equation of the equinoxes (Note 2)
26 *
27 * Notes:
28 *
29 * 1) The TT date date1+date2 is a Julian Date, apportioned in any
30 * convenient way between the two arguments. For example,
31 * JD(TT)=2450123.7 could be expressed in any of these ways,
32 * among others:
33 *
34 * date1 date2
35 *
36 * 2450123.7 0.0 (JD method)
37 * 2451545.0 -1421.3 (J2000 method)
38 * 2400000.5 50123.2 (MJD method)
39 * 2450123.5 0.2 (date & time method)
40 *
41 * The JD method is the most natural and convenient to use in
42 * cases where the loss of several decimal digits of resolution
43 * is acceptable. The J2000 method is best matched to the way
44 * the argument is handled internally and will deliver the
45 * optimum resolution. The MJD method and the date & time methods
46 * are both good compromises between resolution and convenience.
47 *
48 * 2) The result, which is in radians, operates in the following sense:
49 *
50 * Greenwich apparent ST = GMST + equation of the equinoxes
51 *
52 * 3) The result is compatible with the IAU 2000 resolutions. For
53 * further details, see IERS Conventions 2003 and Capitaine et al.
54 * (2002).
55 *
56 * Called:
57 *
58 * gal_pr00 IAU 2000 precession adjustments
59 * gal_obl80 mean obliquity, IAU 1980
60 * gal_nut00a nutation, IAU 2000A
61 * gal_ee00 equation of the equinoxes, IAU 2000
62 *
63 * References:
64 *
65 * Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
66 * implement the IAU 2000 definition of UT1", Astronomy &
67 * Astrophysics, 406, 1135-1149 (2003)
68 *
69 * McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
70 * IERS Technical Note No. 32, BKG (2004)
71 *
72 * This revision:
73 *
74 * 2006 November 13 ( c version 2008 January 18 )
75 *
76 *
77 * Copyright (C) 2008 Paul C. L. Willmott. See notes at end.
78 *
79 *-----------------------------------------------------------------------
80 */
81
82 #include "gal_ee00a.h"
83 #include "gal_pr00.h"
84 #include "gal_obl80.h"
85 #include "gal_nut00a.h"
86 #include "gal_ee00.h"
87
88 double
gal_ee00a(double date1,double date2)89 gal_ee00a
90 (
91 double date1,
92 double date2
93 )
94 {
95
96 double dpsipr, depspr, epsa, dpsi, deps ;
97
98 /*
99 * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
100 */
101
102 /*
103 * IAU 2000 precession-rate adjustments.
104 */
105
106 gal_pr00 ( date1, date2, &dpsipr, &depspr ) ;
107
108 /*
109 * Mean obliquity, consistent with IAU 2000 precession-nutation.
110 */
111
112 epsa = gal_obl80 ( date1, date2 ) + depspr ;
113
114 /*
115 * Nutation in longitude.
116 */
117
118 gal_nut00a ( date1, date2, &dpsi, &deps ) ;
119
120 /*
121 * Equation of the equinoxes.
122 */
123
124 return gal_ee00 ( date1, date2, epsa, dpsi ) ;
125
126 /*
127 * Finished.
128 */
129
130 }
131
132 /*
133 * gal - General Astrodynamics Library
134 * Copyright (C) 2008 Paul C. L. Willmott
135 *
136 * This program is free software; you can redistribute it and/or modify
137 * it under the terms of the GNU General Public License as published by
138 * the Free Software Foundation; either version 2 of the License, or
139 * (at your option) any later version.
140 *
141 * This program is distributed in the hope that it will be useful,
142 * but WITHOUT ANY WARRANTY; without even the implied warranty of
143 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
144 * GNU General Public License for more details.
145 *
146 * You should have received a copy of the GNU General Public License along
147 * with this program; if not, write to the Free Software Foundation, Inc.,
148 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
149 *
150 * Contact:
151 *
152 * Paul Willmott
153 * vp9mu@amsat.org
154 */
155