1 /* 2 * - - - - - - - - - - 3 * g a l _ o b l 8 0 4 * - - - - - - - - - - 5 * 6 * This routine is part of the General Astrodynamics Library 7 * 8 * Description: 9 * 10 * Mean obliquity of the ecliptic, IAU 1980 model. 11 * 12 * This routine is an independent translation of a FORTRAN routine 13 * that is part of IAU's SOFA software collection. 14 * 15 * Status: 16 * 17 * canonical model. 18 * 19 * Given: 20 * 21 * date1,date2 d TT as a 2-part Julian Date (Note 1) 22 * 23 * Returned: 24 * 25 * gal_obl80 d obliquity of the ecliptic (radians, Note 2) 26 * 27 * Notes: 28 * 29 * 1) The TT date date1+date2 is a Julian Date, apportioned in any 30 * convenient way between the two arguments. For example, 31 * JD(TT)=2450123.7 could be expressed in any of these ways, 32 * among others: 33 * 34 * date1 date2 35 * 36 * 2450123.7 0.0 (JD method) 37 * 2451545.0 -1421.3 (J2000 method) 38 * 2400000.5 50123.2 (MJD method) 39 * 2450123.5 0.2 (date & time method) 40 * 41 * The JD method is the most natural and convenient to use in 42 * cases where the loss of several decimal digits of resolution 43 * is acceptable. The J2000 method is best matched to the way 44 * the argument is handled internally and will deliver the 45 * optimum resolution. The MJD method and the date & time methods 46 * are both good compromises between resolution and convenience. 47 * 48 * 2) The result is the angle between the ecliptic and mean equator of 49 * date date1+date2. 50 * 51 * References: 52 * 53 * Explanatory Supplement to the Astronomical Almanac, 54 * P. Kenneth Seidelmann (ed), University Science Books (1992), 55 * Expression 3.222-1 (p114). 56 * 57 * This revision: 58 * 59 * 2006 October 28 ( c version 2008 January 19 ) 60 * 61 * 62 * Copyright (C) 2008 Paul C. L. Willmott. See notes at end. 63 * 64 *----------------------------------------------------------------------- 65 */ 66 67 #ifndef _GAL_OBL80_H_ 68 #define _GAL_OBL80_H_ 1 69 70 #undef __BEGIN_DECLS 71 #undef __END_DECLS 72 #ifdef __cplusplus 73 #define __BEGIN_DECLS extern "C" { 74 #define __END_DECLS } 75 #else 76 #define __BEGIN_DECLS /* empty */ 77 #define __END_DECLS /* empty */ 78 #endif 79 80 __BEGIN_DECLS 81 82 double 83 gal_obl80 84 ( 85 double date1, 86 double date2 87 ) ; 88 89 __END_DECLS 90 91 #endif /* !_GAL_OBL80_H_ */ 92 93 /* 94 * gal - General Astrodynamics Library 95 * Copyright (C) 2008 Paul C. L. Willmott 96 * 97 * This program is free software; you can redistribute it and/or modify 98 * it under the terms of the GNU General Public License as published by 99 * the Free Software Foundation; either version 2 of the License, or 100 * (at your option) any later version. 101 * 102 * This program is distributed in the hope that it will be useful, 103 * but WITHOUT ANY WARRANTY; without even the implied warranty of 104 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 105 * GNU General Public License for more details. 106 * 107 * You should have received a copy of the GNU General Public License along 108 * with this program; if not, write to the Free Software Foundation, Inc., 109 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. 110 * 111 * Contact: 112 * 113 * Paul Willmott 114 * vp9mu@amsat.org 115 */ 116