FACT++  1.0
obl80.c
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1 #include "erfa.h"
2 
3 double eraObl80(double date1, double date2)
4 /*
5 ** - - - - - - - - -
6 ** e r a O b l 8 0
7 ** - - - - - - - - -
8 **
9 ** Mean obliquity of the ecliptic, IAU 1980 model.
10 **
11 ** Given:
12 ** date1,date2 double TT as a 2-part Julian Date (Note 1)
13 **
14 ** Returned (function value):
15 ** double obliquity of the ecliptic (radians, Note 2)
16 **
17 ** Notes:
18 **
19 ** 1) The TT date date1+date2 is a Julian Date, apportioned in any
20 ** convenient way between the two arguments. For example,
21 ** JD(TT)=2450123.7 could be expressed in any of these ways,
22 ** among others:
23 **
24 ** date1 date2
25 **
26 ** 2450123.7 0.0 (JD method)
27 ** 2451545.0 -1421.3 (J2000 method)
28 ** 2400000.5 50123.2 (MJD method)
29 ** 2450123.5 0.2 (date & time method)
30 **
31 ** The JD method is the most natural and convenient to use in
32 ** cases where the loss of several decimal digits of resolution
33 ** is acceptable. The J2000 method is best matched to the way
34 ** the argument is handled internally and will deliver the
35 ** optimum resolution. The MJD method and the date & time methods
36 ** are both good compromises between resolution and convenience.
37 **
38 ** 2) The result is the angle between the ecliptic and mean equator of
39 ** date date1+date2.
40 **
41 ** Reference:
42 **
43 ** Explanatory Supplement to the Astronomical Almanac,
44 ** P. Kenneth Seidelmann (ed), University Science Books (1992),
45 ** Expression 3.222-1 (p114).
46 **
47 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
48 ** Derived, with permission, from the SOFA library. See notes at end of file.
49 */
50 {
51  double t, eps0;
52 
53 /* Interval between fundamental epoch J2000.0 and given date (JC). */
54  t = ((date1 - ERFA_DJ00) + date2) / ERFA_DJC;
55 
56 /* Mean obliquity of date. */
57  eps0 = ERFA_DAS2R * (84381.448 +
58  (-46.8150 +
59  (-0.00059 +
60  ( 0.001813) * t) * t) * t);
61 
62  return eps0;
63 
64 }
65 /*----------------------------------------------------------------------
66 **
67 **
68 ** Copyright (C) 2013-2015, NumFOCUS Foundation.
69 ** All rights reserved.
70 **
71 ** This library is derived, with permission, from the International
72 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
73 ** available from http://www.iausofa.org.
74 **
75 ** The ERFA version is intended to retain identical functionality to
76 ** the SOFA library, but made distinct through different function and
77 ** file names, as set out in the SOFA license conditions. The SOFA
78 ** original has a role as a reference standard for the IAU and IERS,
79 ** and consequently redistribution is permitted only in its unaltered
80 ** state. The ERFA version is not subject to this restriction and
81 ** therefore can be included in distributions which do not support the
82 ** concept of "read only" software.
83 **
84 ** Although the intent is to replicate the SOFA API (other than
85 ** replacement of prefix names) and results (with the exception of
86 ** bugs; any that are discovered will be fixed), SOFA is not
87 ** responsible for any errors found in this version of the library.
88 **
89 ** If you wish to acknowledge the SOFA heritage, please acknowledge
90 ** that you are using a library derived from SOFA, rather than SOFA
91 ** itself.
92 **
93 **
94 ** TERMS AND CONDITIONS
95 **
96 ** Redistribution and use in source and binary forms, with or without
97 ** modification, are permitted provided that the following conditions
98 ** are met:
99 **
100 ** 1 Redistributions of source code must retain the above copyright
101 ** notice, this list of conditions and the following disclaimer.
102 **
103 ** 2 Redistributions in binary form must reproduce the above copyright
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106 ** distribution.
107 **
108 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
109 ** the International Astronomical Union nor the names of its
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112 **
113 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
114 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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116 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
117 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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126 */
ERFA_DJ00
#define ERFA_DJ00
Definition: erfam.h:87
ERFA_DAS2R
#define ERFA_DAS2R
Definition: erfam.h:60
ERFA_DJC
#define ERFA_DJC
Definition: erfam.h:81
eraObl80
double eraObl80(double date1, double date2)
Definition: obl80.c:3
t
TT t
Definition: test_client.c:26