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#ifndef lint
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static const char RCSid[] = "$Id: sun.c,v 2.3 2003/02/22 02:07:24 greg Exp $";
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#endif
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/*
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* SOLAR CALCULATIONS
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*
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* 3/31/87
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*
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*/
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#include <math.h>
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#define PI 3.141592654
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double s_latitude = 0.66; /* site latitude (radians) */
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double s_longitude = 2.13; /* site longitude (radians) */
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double s_meridian = 2.0944; /* standard meridian (radians) */
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int
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jdate( /* Julian date (days into year) */
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int month,
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int day
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)
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{
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static short mo_da[12] = {0,31,59,90,120,151,181,212,243,273,304,334};
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return(mo_da[month-1] + day);
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}
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double
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stadj( /* solar time adjustment from Julian date */
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int jd
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)
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{
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return( 0.170 * sin( (4*PI/373) * (jd - 80) ) -
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0.129 * sin( (2*PI/355) * (jd - 8) ) +
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12 * (s_meridian - s_longitude) / PI );
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}
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double
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sdec( /* solar declination angle from Julian date */
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int jd
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)
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{
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return( 0.4093 * sin( (2*PI/368) * (jd - 81) ) );
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}
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double
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salt( /* solar altitude from solar declination and solar time */
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double sd,
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double st
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)
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{
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return( asin( sin(s_latitude) * sin(sd) -
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cos(s_latitude) * cos(sd) * cos(st*(PI/12)) ) );
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}
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double
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sazi( /* solar azimuth from solar declination and solar time */
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double sd,
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double st
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)
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{
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return( -atan2( cos(sd)*sin(st*(PI/12)),
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-cos(s_latitude)*sin(sd) -
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sin(s_latitude)*cos(sd)*cos(st*(PI/12)) ) );
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}
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