1 /*
2 * - - - - - - - - -
3 * g a l _ e e 0 0
4 * - - - - - - - - -
5 *
6 * This routine is part of the General Astrodynamics Library
7 *
8 * Description:
9 *
10 * The equation of the equinoxes, compatible with IAU 2000 resolutions,
11 * given the nutation in longitude and the mean obliquity.
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 * canonical model.
19 *
20 * Given:
21 *
22 * date1,date2 d TT as a 2-part Julian Date (Note 1)
23 * epsa d mean obliquity (Note 2)
24 * dpsi d nutation in longitude (Note 3)
25 *
26 * Returned:
27 *
28 * gal_ee00 d equation of the equinoxes (Note 4)
29 *
30 * Notes:
31 *
32 * 1) The TT date date1+date2 is a Julian Date, apportioned in any
33 * convenient way between the two arguments. For example,
34 * JD(TT)=2450123.7 could be expressed in any of these ways,
35 * among others:
36 *
37 * date1 date2
38 *
39 * 2450123.7 0.0 (JD method)
40 * 2451545.0 -1421.3 (J2000 method)
41 * 2400000.5 50123.2 (MJD method)
42 * 2450123.5 0.2 (date & time method)
43 *
44 * The JD method is the most natural and convenient to use in
45 * cases where the loss of several decimal digits of resolution
46 * is acceptable. The J2000 method is best matched to the way
47 * the argument is handled internally and will deliver the
48 * optimum resolution. The MJD method and the date & time methods
49 * are both good compromises between resolution and convenience.
50 *
51 * 2) The obliquity, in radians, is mean of date.
52 *
53 * 3) The result, which is in radians, operates in the following sense:
54 *
55 * Greenwich apparent ST = GMST + equation of the equinoxes
56 *
57 * 4) The result is compatible with the IAU 2000 resolutions. For
58 * further details, see IERS Conventions 2003 and Capitaine et al.
59 * (2002).
60 *
61 * Called:
62 *
63 * gal_eect00 equation of the equinoxes complementary terms
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., Petit, G. (eds.), IERS Conventions (2003),
72 * IERS Technical Note No. 32, BKG (2004)
73 *
74 * This revision:
75 *
76 * 2006 November 13 ( c version 2008 January 18 )
77 *
78 *
79 * Copyright (C) 2008 Paul C. L. Willmott. See notes at end.
80 *
81 *-----------------------------------------------------------------------
82 */
83
84 #include <math.h>
85 #include "gal_ee00.h"
86 #include "gal_eect00.h"
87
88 double
gal_ee00(double date1,double date2,double epsa,double dpsi)89 gal_ee00
90 (
91 double date1,
92 double date2,
93 double epsa,
94 double dpsi
95 )
96 {
97
98 /*
99 * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
100 */
101
102 /*
103 * Equation of the equinoxes.
104 */
105
106 return dpsi * cos( epsa ) + gal_eect00 ( date1, date2 ) ;
107
108 /*
109 * Finished.
110 */
111
112 }
113
114 /*
115 * gal - General Astrodynamics Library
116 * Copyright (C) 2008 Paul C. L. Willmott
117 *
118 * This program is free software; you can redistribute it and/or modify
119 * it under the terms of the GNU General Public License as published by
120 * the Free Software Foundation; either version 2 of the License, or
121 * (at your option) any later version.
122 *
123 * This program is distributed in the hope that it will be useful,
124 * but WITHOUT ANY WARRANTY; without even the implied warranty of
125 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
126 * GNU General Public License for more details.
127 *
128 * You should have received a copy of the GNU General Public License along
129 * with this program; if not, write to the Free Software Foundation, Inc.,
130 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
131 *
132 * Contact:
133 *
134 * Paul Willmott
135 * vp9mu@amsat.org
136 */
137