1 /*
2 * - - - - - - - - -
3 * g a l _ p r 0 0
4 * - - - - - - - - -
5 *
6 * This routine is part of the General Astrodynamics Library
7 *
8 * Description:
9 *
10 * Precession-rate part of the IAU 2000 precession-nutation models
11 * (part of MHB2000).
12 *
13 * This routine is an independent translation of a FORTRAN routine
14 * that is part of IAU's SOFA software collection.
15 *
16 * Status:
17 *
18 * canonical model.
19 *
20 * Given:
21 *
22 * date1,date2 d TT as a 2-part Julian Date (Note 1)
23 *
24 * Returned:
25 *
26 * *dpsipr,*deps d precession corrections (Notes 2,3)
27 *
28 * Notes:
29 *
30 * 1) The TT date date1+date2 is a Julian Date, apportioned in any
31 * convenient way between the two arguments. For example,
32 * JD(TT)=2450123.7 could be expressed in any of these ways,
33 * among others:
34 *
35 * date1 date2
36 *
37 * 2450123.7 0.0 (JD method)
38 * 2451545.0 -1421.3 (J2000 method)
39 * 2400000.5 50123.2 (MJD method)
40 * 2450123.5 0.2 (date & time method)
41 *
42 * The JD method is the most natural and convenient to use in
43 * cases where the loss of several decimal digits of resolution
44 * is acceptable. The J2000 method is best matched to the way
45 * the argument is handled internally and will deliver the
46 * optimum resolution. The MJD method and the date & time methods
47 * are both good compromises between resolution and convenience.
48 *
49 * 2) The precession adjustments are expressed as "nutation components",
50 * corrections in longitude and obliquity with respect to the J2000
51 * equinox and ecliptic.
52 *
53 * 3) Although the precession adjustments are stated to be with respect
54 * to Lieske et al. (1977), the MHB2000 model does not specify which
55 * set of Euler angles are to be used and how the adjustments are to
56 * be applied. The most literal and straightforward procedure is to
57 * adopt the 4-rotation epsilon_0, psi_A, omega_A, xi_A option, and
58 * to add dpsipr to psi_A and depspr to both omega_A and eps_A
59 * (Wallace 2002).
60 *
61 * 4) This is an implementation of one aspect of the IAU 2000A nutation
62 * model, formally adopted by the IAU General Assembly in 2000,
63 * namely MHB2000 (Mathews et al. 2002).
64 *
65 * References
66 *
67 * Lieske, J.H., Lederle, T., Fricke, W. & Morando, B., "Expressions
68 * for the precession quantities based upon the IAU (1976) System of
69 * Astronomical Constants", Astron.Astrophys., 58, 1-16 (1977)
70 *
71 * Mathews, P.M., Herring, T.A., Buffet, B.A., "Modeling of nutation
72 * and precession New nutation series for nonrigid Earth and
73 * insights into the Earth's interior", J.Geophys.Res., 107, B4,
74 * 2002. The MHB2000 code itself was obtained on 9th September 2002
75 * from ftp://maia.usno.navy.mil/conv2000/chapter5/IAU2000A.
76 *
77 * Wallace, P.T., "Software for Implementing the IAU 2000
78 * Resolutions", in IERS Workshop 5.1 (2002)
79 *
80 * This revision:
81 *
82 * 2005 August 24 ( c version 2008 January 19 )
83 *
84 *
85 * Copyright (C) 2008 Paul C. L. Willmott. See notes at end.
86 *
87 *-----------------------------------------------------------------------
88 */
89
90 #include "gal_const.h"
91 #include "gal_pr00.h"
92
93 void
gal_pr00(double date1,double date2,double * dpsipr,double * depspr)94 gal_pr00
95 (
96 double date1,
97 double date2,
98 double *dpsipr,
99 double *depspr
100 )
101 {
102
103 /*
104 * ------------------------------------
105 * Precession and obliquity corrections (radians per century)
106 * ------------------------------------
107 */
108
109 const double PRECOR = -0.29965 * GAL_AS2R ;
110 const double OBLCOR = -0.02524 * GAL_AS2R ;
111
112 double t ;
113
114 /*
115 * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
116 */
117
118 /*
119 * Interval between fundamental epoch J2000.0 and given date (JC).
120 */
121
122 t = ( ( date1 - GAL_J2000 ) + date2 ) / GAL_DJC ;
123
124 /*
125 * Precession rate contributions with respect to IAU 1976/80.
126 */
127
128 *dpsipr = PRECOR * t ;
129 *depspr = OBLCOR * t ;
130
131 /*
132 * Finished.
133 */
134
135 }
136
137 /*
138 * gal - General Astrodynamics Library
139 * Copyright (C) 2008 Paul C. L. Willmott
140 *
141 * This program is free software; you can redistribute it and/or modify
142 * it under the terms of the GNU General Public License as published by
143 * the Free Software Foundation; either version 2 of the License, or
144 * (at your option) any later version.
145 *
146 * This program is distributed in the hope that it will be useful,
147 * but WITHOUT ANY WARRANTY; without even the implied warranty of
148 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
149 * GNU General Public License for more details.
150 *
151 * You should have received a copy of the GNU General Public License along
152 * with this program; if not, write to the Free Software Foundation, Inc.,
153 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
154 *
155 * Contact:
156 *
157 * Paul Willmott
158 * vp9mu@amsat.org
159 */
160