1 #include "erfa.h"
2 #include "erfam.h"
3
eraPr00(double date1,double date2,double * dpsipr,double * depspr)4 void eraPr00(double date1, double date2, double *dpsipr, double *depspr)
5 /*
6 ** - - - - - - - -
7 ** e r a P r 0 0
8 ** - - - - - - - -
9 **
10 ** Precession-rate part of the IAU 2000 precession-nutation models
11 ** (part of MHB2000).
12 **
13 ** Given:
14 ** date1,date2 double TT as a 2-part Julian Date (Note 1)
15 **
16 ** Returned:
17 ** dpsipr,depspr double precession corrections (Notes 2,3)
18 **
19 ** Notes:
20 **
21 ** 1) The TT date date1+date2 is a Julian Date, apportioned in any
22 ** convenient way between the two arguments. For example,
23 ** JD(TT)=2450123.7 could be expressed in any of these ways,
24 ** among others:
25 **
26 ** date1 date2
27 **
28 ** 2450123.7 0.0 (JD method)
29 ** 2451545.0 -1421.3 (J2000 method)
30 ** 2400000.5 50123.2 (MJD method)
31 ** 2450123.5 0.2 (date & time method)
32 **
33 ** The JD method is the most natural and convenient to use in
34 ** cases where the loss of several decimal digits of resolution
35 ** is acceptable. The J2000 method is best matched to the way
36 ** the argument is handled internally and will deliver the
37 ** optimum resolution. The MJD method and the date & time methods
38 ** are both good compromises between resolution and convenience.
39 **
40 ** 2) The precession adjustments are expressed as "nutation
41 ** components", corrections in longitude and obliquity with respect
42 ** to the J2000.0 equinox and ecliptic.
43 **
44 ** 3) Although the precession adjustments are stated to be with respect
45 ** to Lieske et al. (1977), the MHB2000 model does not specify which
46 ** set of Euler angles are to be used and how the adjustments are to
47 ** be applied. The most literal and straightforward procedure is to
48 ** adopt the 4-rotation epsilon_0, psi_A, omega_A, xi_A option, and
49 ** to add dpsipr to psi_A and depspr to both omega_A and eps_A.
50 **
51 ** 4) This is an implementation of one aspect of the IAU 2000A nutation
52 ** model, formally adopted by the IAU General Assembly in 2000,
53 ** namely MHB2000 (Mathews et al. 2002).
54 **
55 ** References:
56 **
57 ** Lieske, J.H., Lederle, T., Fricke, W. & Morando, B., "Expressions
58 ** for the precession quantities based upon the IAU (1976) System of
59 ** Astronomical Constants", Astron.Astrophys., 58, 1-16 (1977)
60 **
61 ** Mathews, P.M., Herring, T.A., Buffet, B.A., "Modeling of nutation
62 ** and precession New nutation series for nonrigid Earth and
63 ** insights into the Earth's interior", J.Geophys.Res., 107, B4,
64 ** 2002. The MHB2000 code itself was obtained on 9th September 2002
65 ** from ftp://maia.usno.navy.mil/conv2000/chapter5/IAU2000A.
66 **
67 ** Wallace, P.T., "Software for Implementing the IAU 2000
68 ** Resolutions", in IERS Workshop 5.1 (2002).
69 **
70 ** This revision: 2021 May 11
71 **
72 ** Copyright (C) 2013-2021, NumFOCUS Foundation.
73 ** Derived, with permission, from the SOFA library. See notes at end of file.
74 */
75 {
76 double t;
77
78 /* Precession and obliquity corrections (radians per century) */
79 static const double PRECOR = -0.29965 * ERFA_DAS2R,
80 OBLCOR = -0.02524 * ERFA_DAS2R;
81
82
83 /* Interval between fundamental epoch J2000.0 and given date (JC). */
84 t = ((date1 - ERFA_DJ00) + date2) / ERFA_DJC;
85
86 /* Precession rate contributions with respect to IAU 1976/80. */
87 *dpsipr = PRECOR * t;
88 *depspr = OBLCOR * t;
89
90 /* Finished. */
91
92 }
93 /*----------------------------------------------------------------------
94 **
95 **
96 ** Copyright (C) 2013-2021, NumFOCUS Foundation.
97 ** All rights reserved.
98 **
99 ** This library is derived, with permission, from the International
100 ** Astronomical Union's "Standards of Fundamental Astronomy" library,
101 ** available from http://www.iausofa.org.
102 **
103 ** The ERFA version is intended to retain identical functionality to
104 ** the SOFA library, but made distinct through different function and
105 ** file names, as set out in the SOFA license conditions. The SOFA
106 ** original has a role as a reference standard for the IAU and IERS,
107 ** and consequently redistribution is permitted only in its unaltered
108 ** state. The ERFA version is not subject to this restriction and
109 ** therefore can be included in distributions which do not support the
110 ** concept of "read only" software.
111 **
112 ** Although the intent is to replicate the SOFA API (other than
113 ** replacement of prefix names) and results (with the exception of
114 ** bugs; any that are discovered will be fixed), SOFA is not
115 ** responsible for any errors found in this version of the library.
116 **
117 ** If you wish to acknowledge the SOFA heritage, please acknowledge
118 ** that you are using a library derived from SOFA, rather than SOFA
119 ** itself.
120 **
121 **
122 ** TERMS AND CONDITIONS
123 **
124 ** Redistribution and use in source and binary forms, with or without
125 ** modification, are permitted provided that the following conditions
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127 **
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130 **
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134 ** distribution.
135 **
136 ** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
137 ** the International Astronomical Union nor the names of its
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139 ** from this software without specific prior written permission.
140 **
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154 */
155