1 /* 2 3 -Procedure b1950_c ( Besselian Date 1950.0 ) 4 5 -Abstract 6 7 Return the Julian Date corresponding to Besselian Date 1950.0. 8 9 -Disclaimer 10 11 THIS SOFTWARE AND ANY RELATED MATERIALS WERE CREATED BY THE 12 CALIFORNIA INSTITUTE OF TECHNOLOGY (CALTECH) UNDER A U.S. 13 GOVERNMENT CONTRACT WITH THE NATIONAL AERONAUTICS AND SPACE 14 ADMINISTRATION (NASA). THE SOFTWARE IS TECHNOLOGY AND SOFTWARE 15 PUBLICLY AVAILABLE UNDER U.S. EXPORT LAWS AND IS PROVIDED "AS-IS" 16 TO THE RECIPIENT WITHOUT WARRANTY OF ANY KIND, INCLUDING ANY 17 WARRANTIES OF PERFORMANCE OR MERCHANTABILITY OR FITNESS FOR A 18 PARTICULAR USE OR PURPOSE (AS SET FORTH IN UNITED STATES UCC 19 SECTIONS 2312-2313) OR FOR ANY PURPOSE WHATSOEVER, FOR THE 20 SOFTWARE AND RELATED MATERIALS, HOWEVER USED. 21 22 IN NO EVENT SHALL CALTECH, ITS JET PROPULSION LABORATORY, OR NASA 23 BE LIABLE FOR ANY DAMAGES AND/OR COSTS, INCLUDING, BUT NOT 24 LIMITED TO, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND, 25 INCLUDING ECONOMIC DAMAGE OR INJURY TO PROPERTY AND LOST PROFITS, 26 REGARDLESS OF WHETHER CALTECH, JPL, OR NASA BE ADVISED, HAVE 27 REASON TO KNOW, OR, IN FACT, SHALL KNOW OF THE POSSIBILITY. 28 29 RECIPIENT BEARS ALL RISK RELATING TO QUALITY AND PERFORMANCE OF 30 THE SOFTWARE AND ANY RELATED MATERIALS, AND AGREES TO INDEMNIFY 31 CALTECH AND NASA FOR ALL THIRD-PARTY CLAIMS RESULTING FROM THE 32 ACTIONS OF RECIPIENT IN THE USE OF THE SOFTWARE. 33 34 -Required_Reading 35 36 None. 37 38 -Keywords 39 40 CONSTANTS 41 42 */ 43 44 #include "SpiceUsr.h" 45 b1950_c(void)46 SpiceDouble b1950_c ( void ) 47 48 /* 49 50 -Brief_I/O 51 52 The function returns the Julian Date corresponding to Besselian 53 date 1950.0. 54 55 -Detailed_Input 56 57 None. 58 59 -Detailed_Output 60 61 The function returns 2433282.42345905, the Julian Date corresponding 62 to Besselian Date 1950.0 as reported by Lieske [1]. 63 64 -Parameters 65 66 None. 67 68 -Exceptions 69 70 Error free. 71 72 -Files 73 74 None. 75 76 -Particulars 77 78 Lieske [1] defines a mapping from Julian Ephemeris Date 79 to Besselian: 80 81 BE = 1900. + (JED - 2415020.31352)/365.242198781 82 83 The inverse mapping being: 84 85 JED = (BE - 1900.)*365.242198781 + 2415020.31352 86 87 -Examples 88 89 The following code fragment illustrates the use of b1950_c. 90 91 /. 92 Convert Julian Date to UTC seconds past the reference 93 epoch (b1950_c). 94 ./ 95 96 spref = ( jd - b1950_c() ) * spd_c(); 97 98 -Restrictions 99 100 None. 101 102 -Literature_References 103 104 [1] Jay Lieske, ``Precession Matrix Based on IAU (1976) 105 System of Astronomical Constants,'' Astron. Astrophys. 106 73, 282-284 (1979). 107 108 -Author_and_Institution 109 110 W.L. Taber (JPL) 111 I.M. Underwood (JPL) 112 113 -Version 114 115 -CSPICE Version 2.0.0, 01-SEP-2005 (EDW) 116 117 This routine now returns the value reported in the Lieske 118 paper: 119 120 2433282.42345905 121 122 The same value returned by the FORTRAN SPICELIB routine 123 B1950. 124 125 This routine previously returned the value reported in the 126 "Explanatory Supplement to the Astronomical Almanac", 1992, 127 page 699: 128 129 2433282.423 130 131 The ESAA value describing a truncation of the Lieske value. 132 The difference between the two values expressed as seconds 133 yields approximately 39.662 seconds. 134 135 -CSPICE Version 1.0.1, 08-FEB-1998 (EDW) 136 137 Corrected and clarified header entries. 138 139 -CSPICE Version 1.0.0, 25-OCT-1997 (EDW) 140 141 -Index_Entries 142 143 besselian date 1950.0 144 145 -& 146 */ 147 148 { /* Begin b1950_c */ 149 150 151 return 2433282.42345905; 152 153 154 } /* End b1950_c */ 155