mirror of https://github.com/XEphem/XEphem.git
26 lines
555 B
C
26 lines
555 B
C
#include <stdio.h>
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#include "astro.h"
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/* given the modified Julian date, mj, find the mean obliquity of the
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* ecliptic, *eps, in radians.
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*
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* IAU expression (see e.g. Astron. Almanac 1984); stern
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*/
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void
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obliquity (double mj, double *eps)
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{
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static double lastmj = -16347, lasteps;
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if (mj != lastmj) {
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double t = (mj - J2000)/36525.; /* centuries from J2000 */
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lasteps = degrad(23.4392911 + /* 23^ 26' 21".448 */
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t * (-46.8150 +
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t * ( -0.00059 +
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t * ( 0.001813 )))/3600.0);
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lastmj = mj;
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}
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*eps = lasteps;
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}
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