source: Sophya/trunk/SophyaExt/XephemAstroLib/obliq.c@ 3148

#include <stdio.h>

#include "astro.h"

/* given the modified Julian date, mj, find the mean obliquity of the
 * ecliptic, *eps, in radians.
 *
 * IAU expression (see e.g. Astron. Almanac 1984); stern
 */
void
obliquity (double mj, double *eps)
{
        static double lastmj = -16347, lasteps;

        if (mj != lastmj) {
            double t = (mj - J2000)/36525.;     /* centuries from J2000 */
            lasteps = degrad(23.4392911 +       /* 23^ 26' 21".448 */
                            t * (-46.8150 +
                            t * ( -0.00059 +
                            t * (  0.001813 )))/3600.0);
            lastmj = mj;
        }
        *eps = lasteps;
}

/* For RCS Only -- Do Not Edit */
static char *rcsid[2] = {(char *)rcsid, "@(#) $RCSfile: obliq.c,v $ $Date: 2006-11-22 13:53:30 $ $Revision: 1.6 $ $Name: not supported by cvs2svn $"};