source: trunk/FACT++/sofa/src/obl80.c@ 18375

Last change on this file since 18375 was 18346, checked in by tbretz, 11 years ago
File size: 6.3 KB
Line 
1#include "sofa.h"
2
3double iauObl80(double date1, double date2)
4/*
5** - - - - - - - - -
6** i a u O b l 8 0
7** - - - - - - - - -
8**
9** Mean obliquity of the ecliptic, IAU 1980 model.
10**
11** This function is part of the International Astronomical Union's
12** SOFA (Standards Of Fundamental Astronomy) software collection.
13**
14** Status: canonical model.
15**
16** Given:
17** date1,date2 double TT as a 2-part Julian Date (Note 1)
18**
19** Returned (function value):
20** double obliquity of the ecliptic (radians, Note 2)
21**
22** Notes:
23**
24** 1) The TT date date1+date2 is a Julian Date, apportioned in any
25** convenient way between the two arguments. For example,
26** JD(TT)=2450123.7 could be expressed in any of these ways,
27** among others:
28**
29** date1 date2
30**
31** 2450123.7 0.0 (JD method)
32** 2451545.0 -1421.3 (J2000 method)
33** 2400000.5 50123.2 (MJD method)
34** 2450123.5 0.2 (date & time method)
35**
36** The JD method is the most natural and convenient to use in
37** cases where the loss of several decimal digits of resolution
38** is acceptable. The J2000 method is best matched to the way
39** the argument is handled internally and will deliver the
40** optimum resolution. The MJD method and the date & time methods
41** are both good compromises between resolution and convenience.
42**
43** 2) The result is the angle between the ecliptic and mean equator of
44** date date1+date2.
45**
46** Reference:
47**
48** Explanatory Supplement to the Astronomical Almanac,
49** P. Kenneth Seidelmann (ed), University Science Books (1992),
50** Expression 3.222-1 (p114).
51**
52** This revision: 2013 June 18
53**
54** SOFA release 2015-02-09
55**
56** Copyright (C) 2015 IAU SOFA Board. See notes at end.
57*/
58{
59 double t, eps0;
60
61/* Interval between fundamental epoch J2000.0 and given date (JC). */
62 t = ((date1 - DJ00) + date2) / DJC;
63
64/* Mean obliquity of date. */
65 eps0 = DAS2R * (84381.448 +
66 (-46.8150 +
67 (-0.00059 +
68 ( 0.001813) * t) * t) * t);
69
70 return eps0;
71
72/*----------------------------------------------------------------------
73**
74** Copyright (C) 2015
75** Standards Of Fundamental Astronomy Board
76** of the International Astronomical Union.
77**
78** =====================
79** SOFA Software License
80** =====================
81**
82** NOTICE TO USER:
83**
84** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
85** CONDITIONS WHICH APPLY TO ITS USE.
86**
87** 1. The Software is owned by the IAU SOFA Board ("SOFA").
88**
89** 2. Permission is granted to anyone to use the SOFA software for any
90** purpose, including commercial applications, free of charge and
91** without payment of royalties, subject to the conditions and
92** restrictions listed below.
93**
94** 3. You (the user) may copy and distribute SOFA source code to others,
95** and use and adapt its code and algorithms in your own software,
96** on a world-wide, royalty-free basis. That portion of your
97** distribution that does not consist of intact and unchanged copies
98** of SOFA source code files is a "derived work" that must comply
99** with the following requirements:
100**
101** a) Your work shall be marked or carry a statement that it
102** (i) uses routines and computations derived by you from
103** software provided by SOFA under license to you; and
104** (ii) does not itself constitute software provided by and/or
105** endorsed by SOFA.
106**
107** b) The source code of your derived work must contain descriptions
108** of how the derived work is based upon, contains and/or differs
109** from the original SOFA software.
110**
111** c) The names of all routines in your derived work shall not
112** include the prefix "iau" or "sofa" or trivial modifications
113** thereof such as changes of case.
114**
115** d) The origin of the SOFA components of your derived work must
116** not be misrepresented; you must not claim that you wrote the
117** original software, nor file a patent application for SOFA
118** software or algorithms embedded in the SOFA software.
119**
120** e) These requirements must be reproduced intact in any source
121** distribution and shall apply to anyone to whom you have
122** granted a further right to modify the source code of your
123** derived work.
124**
125** Note that, as originally distributed, the SOFA software is
126** intended to be a definitive implementation of the IAU standards,
127** and consequently third-party modifications are discouraged. All
128** variations, no matter how minor, must be explicitly marked as
129** such, as explained above.
130**
131** 4. You shall not cause the SOFA software to be brought into
132** disrepute, either by misuse, or use for inappropriate tasks, or
133** by inappropriate modification.
134**
135** 5. The SOFA software is provided "as is" and SOFA makes no warranty
136** as to its use or performance. SOFA does not and cannot warrant
137** the performance or results which the user may obtain by using the
138** SOFA software. SOFA makes no warranties, express or implied, as
139** to non-infringement of third party rights, merchantability, or
140** fitness for any particular purpose. In no event will SOFA be
141** liable to the user for any consequential, incidental, or special
142** damages, including any lost profits or lost savings, even if a
143** SOFA representative has been advised of such damages, or for any
144** claim by any third party.
145**
146** 6. The provision of any version of the SOFA software under the terms
147** and conditions specified herein does not imply that future
148** versions will also be made available under the same terms and
149** conditions.
150*
151** In any published work or commercial product which uses the SOFA
152** software directly, acknowledgement (see www.iausofa.org) is
153** appreciated.
154**
155** Correspondence concerning SOFA software should be addressed as
156** follows:
157**
158** By email: sofa@ukho.gov.uk
159** By post: IAU SOFA Center
160** HM Nautical Almanac Office
161** UK Hydrographic Office
162** Admiralty Way, Taunton
163** Somerset, TA1 2DN
164** United Kingdom
165**
166**--------------------------------------------------------------------*/
167}
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