FACT++  1.0
sp00.c
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1 #include "erfa.h"
2 
3 double 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) 2013-2015, NumFOCUS Foundation.
51 ** Derived, with permission, from the SOFA library. See notes at end of file.
52 */
53 {
54  double t, sp;
55 
56 /* Interval between fundamental epoch J2000.0 and current date (JC). */
57  t = ((date1 - ERFA_DJ00) + date2) / ERFA_DJC;
58 
59 /* Approximate s'. */
60  sp = -47e-6 * t * ERFA_DAS2R;
61 
62  return sp;
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
104 ** notice, this list of conditions and the following disclaimer in
105 ** the documentation and/or other materials provided with the
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
110 ** contributors may be used to endorse or promote products derived
111 ** from this software without specific prior written permission.
112 **
113 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
114 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
115 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
116 ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
117 ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
118 ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
119 ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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124 ** POSSIBILITY OF SUCH DAMAGE.
125 **
126 */
ERFA_DJ00
#define ERFA_DJ00
Definition: erfam.h:87
eraSp00
double eraSp00(double date1, double date2)
Definition: sp00.c:3
ERFA_DAS2R
#define ERFA_DAS2R
Definition: erfam.h:60
ERFA_DJC
#define ERFA_DJC
Definition: erfam.h:81
t
TT t
Definition: test_client.c:26