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#include <stdio.h>
#include <math.h>
#include "P_.h"
#include "astro.h"
#include "vsop87.h"
/* given the modified JD, mjd, return the true geocentric ecliptic longitude
* of the sun for the mean equinox of the date, *lsn, in radians, the
* sun-earth distance, *rsn, in AU, and the latitude *bsn, in radians
* (since this is always <= 1.2 arcseconds, in can be neglected by
* calling with bsn = NULL).
*
* if the APPARENT ecliptic longitude is required, correct the longitude for
* nutation to the true equinox of date and for aberration (light travel time,
* approximately -9.27e7/186000/(3600*24*365)*2*pi = -9.93e-5 radians).
*/
void
sunpos (mjd, lsn, rsn, bsn)
double mjd;
double *lsn, *rsn, *bsn;
{
static double last_mjd = -3691, last_lsn, last_rsn, last_bsn;
double ret[6];
if (mjd == last_mjd) {
*lsn = last_lsn;
*rsn = last_rsn;
if (bsn) *bsn = last_bsn;
return;
}
vsop87(mjd, SUN, 0.0, ret); /* full precision earth pos */
*lsn = ret[0] - PI; /* revert to sun pos */
range (lsn, 2*PI); /* normalise */
last_lsn = *lsn; /* memorise */
last_rsn = *rsn = ret[2];
last_bsn = -ret[1];
last_mjd = mjd;
if (bsn) *bsn = last_bsn; /* assign only if non-NULL pointer */
}
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