source: trunk/FACT++/erfa/src/sp00.c@ 18711

Last change on this file since 18711 was 18711, checked in by tbretz, 9 years ago
Updated to ERFA 1.3.0 (no relevant code change except the leap second at the beginning of 2017)
File size: 5.0 KB
Line 
1#include "erfa.h"
2
3double eraSp00(double date1, double date2)
4/*
5** - - - - - - - -
6** e r a S p 0 0
7** - - - - - - - -
8**
9** The TIO locator s', positioning the Terrestrial Intermediate Origin
10** on the equator of the Celestial Intermediate Pole.
11**
12** Given:
13** date1,date2 double TT as a 2-part Julian Date (Note 1)
14**
15** Returned (function value):
16** double the TIO locator s' in radians (Note 2)
17**
18** Notes:
19**
20** 1) The TT date date1+date2 is a Julian Date, apportioned in any
21** convenient way between the two arguments. For example,
22** JD(TT)=2450123.7 could be expressed in any of these ways,
23** among others:
24**
25** date1 date2
26**
27** 2450123.7 0.0 (JD method)
28** 2451545.0 -1421.3 (J2000 method)
29** 2400000.5 50123.2 (MJD method)
30** 2450123.5 0.2 (date & time method)
31**
32** The JD method is the most natural and convenient to use in
33** cases where the loss of several decimal digits of resolution
34** is acceptable. The J2000 method is best matched to the way
35** the argument is handled internally and will deliver the
36** optimum resolution. The MJD method and the date & time methods
37** are both good compromises between resolution and convenience.
38**
39** 2) The TIO locator s' is obtained from polar motion observations by
40** numerical integration, and so is in essence unpredictable.
41** However, it is dominated by a secular drift of about
42** 47 microarcseconds per century, which is the approximation
43** evaluated by the present function.
44**
45** Reference:
46**
47** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
48** IERS Technical Note No. 32, BKG (2004)
49**
50** Copyright (C) 2013-2016, NumFOCUS Foundation.
51** Derived, with permission, from the SOFA library. See notes at end of file.
52*/
53{
54 double t, sp;
55
56
57/* Interval between fundamental epoch J2000.0 and current date (JC). */
58 t = ((date1 - ERFA_DJ00) + date2) / ERFA_DJC;
59
60/* Approximate s'. */
61 sp = -47e-6 * t * ERFA_DAS2R;
62
63 return sp;
64
65}
66/*----------------------------------------------------------------------
67**
68**
69** Copyright (C) 2013-2016, NumFOCUS Foundation.
70** All rights reserved.
71**
72** This library is derived, with permission, from the International
73** Astronomical Union's "Standards of Fundamental Astronomy" library,
74** available from http://www.iausofa.org.
75**
76** The ERFA version is intended to retain identical functionality to
77** the SOFA library, but made distinct through different function and
78** file names, as set out in the SOFA license conditions. The SOFA
79** original has a role as a reference standard for the IAU and IERS,
80** and consequently redistribution is permitted only in its unaltered
81** state. The ERFA version is not subject to this restriction and
82** therefore can be included in distributions which do not support the
83** concept of "read only" software.
84**
85** Although the intent is to replicate the SOFA API (other than
86** replacement of prefix names) and results (with the exception of
87** bugs; any that are discovered will be fixed), SOFA is not
88** responsible for any errors found in this version of the library.
89**
90** If you wish to acknowledge the SOFA heritage, please acknowledge
91** that you are using a library derived from SOFA, rather than SOFA
92** itself.
93**
94**
95** TERMS AND CONDITIONS
96**
97** Redistribution and use in source and binary forms, with or without
98** modification, are permitted provided that the following conditions
99** are met:
100**
101** 1 Redistributions of source code must retain the above copyright
102** notice, this list of conditions and the following disclaimer.
103**
104** 2 Redistributions in binary form must reproduce the above copyright
105** notice, this list of conditions and the following disclaimer in
106** the documentation and/or other materials provided with the
107** distribution.
108**
109** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
110** the International Astronomical Union nor the names of its
111** contributors may be used to endorse or promote products derived
112** from this software without specific prior written permission.
113**
114** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
115** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
116** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
117** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
118** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
119** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
120** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
121** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
122** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
123** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
124** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
125** POSSIBILITY OF SUCH DAMAGE.
126**
127*/
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