source: Sophya/trunk/SophyaExt/XephemAstroLib/obliq.c@ 2863

Last change on this file since 2863 was 2818, checked in by cmv, 20 years ago

Update de Xephem 3.7 cmv 21/08/2005
File size: 740 bytes
Line 
1#include <stdio.h>
2
3#include "astro.h"
4
5/* given the modified Julian date, mj, find the mean obliquity of the
6 * ecliptic, *eps, in radians.
7 *
8 * IAU expression (see e.g. Astron. Almanac 1984); stern
9 */
10void
11obliquity (double mj, double *eps)
12{
13 static double lastmj = -16347, lasteps;
14
15 if (mj != lastmj) {
16 double t = (mj - J2000)/36525.; /* centuries from J2000 */
17 lasteps = degrad(23.4392911 + /* 23^ 26' 21".448 */
18 t * (-46.8150 +
19 t * ( -0.00059 +
20 t * ( 0.001813 )))/3600.0);
21 lastmj = mj;
22 }
23 *eps = lasteps;
24}
25
26/* For RCS Only -- Do Not Edit */
27static char *rcsid[2] = {(char *)rcsid, "@(#) $RCSfile: obliq.c,v $ $Date: 2005-08-21 10:02:38 $ $Revision: 1.5 $ $Name: not supported by cvs2svn $"};
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