1 /*
2  *  - - - - - - - - - -
3  *   g a l _ o b l 8 0
4  *  - - - - - - - - - -
5  *
6  *  This routine is part of the General Astrodynamics Library
7  *
8  *  Description:
9  *
10  *  Mean obliquity of the ecliptic, IAU 1980 model.
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  *     canonical model.
18  *
19  *  Given:
20  *
21  *     date1,date2         d        TT as a 2-part Julian Date (Note 1)
22  *
23  *  Returned:
24  *
25  *     gal_obl80           d        obliquity of the ecliptic (radians, 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 is the angle between the ecliptic and mean equator of
49  *     date date1+date2.
50  *
51  *  References:
52  *
53  *     Explanatory Supplement to the Astronomical Almanac,
54  *     P. Kenneth Seidelmann (ed), University Science Books (1992),
55  *     Expression 3.222-1 (p114).
56  *
57  *  This revision:
58  *
59  *     2006 October 28 ( c version 2008 January 19 )
60  *
61  *
62  *  Copyright (C) 2008 Paul C. L. Willmott. See notes at end.
63  *
64  *-----------------------------------------------------------------------
65  */
66 
67 #ifndef _GAL_OBL80_H_
68 #define _GAL_OBL80_H_ 1
69 
70 #undef __BEGIN_DECLS
71 #undef __END_DECLS
72 #ifdef __cplusplus
73 #define __BEGIN_DECLS extern "C" {
74 #define __END_DECLS }
75 #else
76 #define __BEGIN_DECLS /* empty */
77 #define __END_DECLS   /* empty */
78 #endif
79 
80 __BEGIN_DECLS
81 
82 double
83 gal_obl80
84  (
85     double date1,
86     double date2
87  ) ;
88 
89 __END_DECLS
90 
91 #endif /* !_GAL_OBL80_H_ */
92 
93 /*
94  *  gal - General Astrodynamics Library
95  *  Copyright (C) 2008 Paul C. L. Willmott
96  *
97  *  This program is free software; you can redistribute it and/or modify
98  *  it under the terms of the GNU General Public License as published by
99  *  the Free Software Foundation; either version 2 of the License, or
100  *  (at your option) any later version.
101  *
102  *  This program is distributed in the hope that it will be useful,
103  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
104  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
105  *  GNU General Public License for more details.
106  *
107  *  You should have received a copy of the GNU General Public License along
108  *  with this program; if not, write to the Free Software Foundation, Inc.,
109  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
110  *
111  *  Contact:
112  *
113  *  Paul Willmott
114  *  vp9mu@amsat.org
115  */
116