Subversion Repositories planix.SVN

#include "astro.h"

static  double  elem[] =
{
        36525.0,                // [0] eday of epoc

        39.48168677,            // [1] semi major axis (au)
        0.24880766,             // [2] eccentricity
        17.14175,               // [3] inclination (deg)
        110.30347,              // [4] longitude of the ascending node (deg)
        224.06676,              // [5] longitude of perihelion (deg)
        238.92881,              // [6] mean longitude (deg)

        -0.00076912,            // [1+6] (au/julian century)
        0.00006465,             // [2+6] (e/julian century)
        11.07,                  // [3+6] (arcsec/julian century)
        -37.33,                 // [4+6] (arcsec/julian century)
        -132.25,                // [5+6] (arcsec/julian century)
        522747.90,              // [6+6] (arcsec/julian century)
};

void
plut(void)
{
        double pturbl, pturbb, pturbr;
        double lograd;
        double dele, enom, vnom, nd, sl;

        double capj, capn, eye, comg, omg;
        double sb, su, cu, u, b, up;
        double sd, ca, sa;

        double cy;

        cy = (eday - elem[0]) / 36525.;         // per julian century

        mrad = elem[1] + elem[1+6]*cy;
        ecc = elem[2] + elem[2+6]*cy;

        cy = cy / 3600;                         // arcsec/deg per julian century
        incl = elem[3] + elem[3+6]*cy;
        node = elem[4] + elem[4+6]*cy;
        argp = elem[5] + elem[5+6]*cy;

        anom = elem[6] + elem[6+6]*cy - argp;
        motion = elem[6+6] / 36525. / 3600;

        incl *= radian;
        node *= radian;
        argp *= radian;
        anom = fmod(anom,360.)*radian;

        enom = anom + ecc*sin(anom);
        do {
                dele = (anom - enom + ecc * sin(enom)) /
                        (1. - ecc*cos(enom));
                enom += dele;
        } while(fabs(dele) > converge);
        vnom = 2.*atan2(sqrt((1.+ecc)/(1.-ecc))*sin(enom/2.),
                cos(enom/2.));
        rad = mrad*(1. - ecc*cos(enom));

        lambda = vnom + argp;
        pturbl = 0.;
        lambda += pturbl*radsec;
        pturbb = 0.;
        pturbr = 0.;

/*
 *      reduce to the ecliptic
 */

        nd = lambda - node;
        lambda = node + atan2(sin(nd)*cos(incl),cos(nd));

        sl = sin(incl)*sin(nd) + pturbb*radsec;
        beta = atan2(sl, pyth(sl));

        lograd = pturbr*2.30258509;
        rad *= 1. + lograd;


        lambda -= 1185.*radsec;
        beta -= 51.*radsec;

        motion *= radian*mrad*mrad/(rad*rad);
        semi = 83.33;

/*
 *      here begins the computation of magnitude
 *      first find the geocentric equatorial coordinates of Saturn
 */

        sd = rad*(cos(beta)*sin(lambda)*sin(obliq) +
                sin(beta)*cos(obliq));
        sa = rad*(cos(beta)*sin(lambda)*cos(obliq) -
                sin(beta)*sin(obliq));
        ca = rad*cos(beta)*cos(lambda);
        sd += zms;
        sa += yms;
        ca += xms;
        alpha = atan2(sa,ca);
        delta = atan2(sd,sqrt(sa*sa+ca*ca));

/*
 *      here are the necessary elements of Saturn's rings
 *      cf. Exp. Supp. p. 363ff.
 */

        capj = 6.9056 - 0.4322*capt;
        capn = 126.3615 + 3.9894*capt + 0.2403*capt2;
        eye = 28.0743 - 0.0128*capt;
        comg = 168.1179 + 1.3936*capt;
        omg = 42.9236 - 2.7390*capt - 0.2344*capt2;

        capj *= radian;
        capn *= radian;
        eye *= radian;
        comg *= radian;
        omg *= radian;

/*
 *      now find saturnicentric ring-plane coords of the earth
 */

        sb = sin(capj)*cos(delta)*sin(alpha-capn) -
                cos(capj)*sin(delta);
        su = cos(capj)*cos(delta)*sin(alpha-capn) +
                sin(capj)*sin(delta);
        cu = cos(delta)*cos(alpha-capn);
        u = atan2(su,cu);
        b = atan2(sb,sqrt(su*su+cu*cu));

/*
 *      and then the saturnicentric ring-plane coords of the sun
 */

        su = sin(eye)*sin(beta) +
                cos(eye)*cos(beta)*sin(lambda-comg);
        cu = cos(beta)*cos(lambda-comg);
        up = atan2(su,cu);

/*
 *      at last, the magnitude
 */


        sb = sin(b);
        mag = -8.68 +2.52*fabs(up+omg-u)-
                2.60*fabs(sb) + 1.25*(sb*sb);

        helio();
        geo();
}