1 /*
2 * - - - - - - - - - -
3 * g a l _ e e 0 0 b
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 but
11 * using the truncated nutation model IAU 2000B.
12 *
13 * This routine is an independent translation of a FORTRAN routine
14 * that is part of IAU's SOFA software collection.
15 *
16 * Status:
17 *
18 * support routine.
19 *
20 * Given:
21 *
22 * date1,date2 d TT as a 2-part Julian Date (Note 1)
23 *
24 * Returned:
25 *
26 * gal_ee00b d equation of the equinoxes (Note 2)
27 *
28 * Notes:
29 *
30 * 1) The TT date date1+date2 is a Julian Date, apportioned in any
31 * convenient way between the two arguments. For example,
32 * JD(TT)=2450123.7 could be expressed in any of these ways,
33 * among others:
34 *
35 * date1 date2
36 *
37 * 2450123.7 0.0 (JD method)
38 * 2451545.0 -1421.3 (J2000 method)
39 * 2400000.5 50123.2 (MJD method)
40 * 2450123.5 0.2 (date & time method)
41 *
42 * The JD method is the most natural and convenient to use in
43 * cases where the loss of several decimal digits of resolution
44 * is acceptable. The J2000 method is best matched to the way
45 * the argument is handled internally and will deliver the
46 * optimum resolution. The MJD method and the date & time methods
47 * are both good compromises between resolution and convenience.
48 *
49 * 2) The result, which is in radians, operates in the following sense:
50 *
51 * Greenwich apparent ST = GMST + equation of the equinoxes
52 *
53 * 3) The result is compatible with the IAU 2000 resolutions except that
54 * accuracy has been compromised for the sake of speed. For further
55 * details, see McCarthy & Luzum (2001), IERS Conventions 2003 and
56 * Capitaine et al. (2003).
57 *
58 * Called:
59 *
60 * gal_pr00 IAU 2000 precession adjustments
61 * gal_obl80 mean obliquity, IAU 1980
62 * gal_nut00b nutation, IAU 2000B
63 * gal_ee00 equation of the equinoxes, IAU 2000
64 *
65 * References:
66 *
67 * Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
68 * implement the IAU 2000 definition of UT1", Astronomy &
69 * Astrophysics, 406, 1135-1149 (2003)
70 *
71 * McCarthy, D.D. & Luzum, B.J., "An abridged model of the
72 * precession-nutation of the celestial pole", Celestial Mechanics &
73 * Dynamical Astronomy, 85, 37-49 (2003)
74 *
75 * McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
76 * IERS Technical Note No. 32, BKG (2004)
77 *
78 * This revision:
79 *
80 * 2006 November 13 ( c version 2008 January 18 )
81 *
82 *
83 * Copyright (C) 2008 Paul C. L. Willmott. See notes at end.
84 *
85 *-----------------------------------------------------------------------
86 */
87
88 #include "gal_ee00b.h"
89 #include "gal_pr00.h"
90 #include "gal_obl80.h"
91 #include "gal_nut00b.h"
92 #include "gal_ee00.h"
93
94 double
gal_ee00b(double date1,double date2)95 gal_ee00b
96 (
97 double date1,
98 double date2
99 )
100 {
101
102 double dpsipr, depspr, epsa, dpsi, deps ;
103
104 /*
105 * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
106 */
107
108 /*
109 * IAU 2000 precession-rate adjustments.
110 */
111
112 gal_pr00 ( date1, date2, &dpsipr, &depspr ) ;
113
114 /*
115 * Mean obliquity, consistent with IAU 2000 precession-nutation.
116 */
117
118 epsa = gal_obl80 ( date1, date2 ) + depspr ;
119
120 /*
121 * Nutation in longitude.
122 */
123
124 gal_nut00b ( date1, date2, &dpsi, &deps ) ;
125
126 /*
127 * Equation of the equinoxes.
128 */
129
130 return gal_ee00 ( date1, date2, epsa, dpsi ) ;
131
132 /*
133 * Finished.
134 */
135
136 }
137
138 /*
139 * gal - General Astrodynamics Library
140 * Copyright (C) 2008 Paul C. L. Willmott
141 *
142 * This program is free software; you can redistribute it and/or modify
143 * it under the terms of the GNU General Public License as published by
144 * the Free Software Foundation; either version 2 of the License, or
145 * (at your option) any later version.
146 *
147 * This program is distributed in the hope that it will be useful,
148 * but WITHOUT ANY WARRANTY; without even the implied warranty of
149 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
150 * GNU General Public License for more details.
151 *
152 * You should have received a copy of the GNU General Public License along
153 * with this program; if not, write to the Free Software Foundation, Inc.,
154 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
155 *
156 * Contact:
157 *
158 * Paul Willmott
159 * vp9mu@amsat.org
160 */
161