Subversion Repositories planix.SVN

#include "astro.h"

void
nutate(void)
{

/*
 *      uses radian, radsec
 *      sets phi, eps, dphi, deps, obliq, gst, tobliq
 */

        double msun, mnom, noded, dmoon;

/*
 *      nutation of the equinoxes is a wobble of the pole
 *      of the earths rotation whose magnitude is about
 *      9 seconds of arc and whose period is about 18.6 years.
 *
 *      it depends upon the pull of the sun and moon on the
 *      equatorial bulge of the earth.
 *
 *      phi and eps are the two angles which specify the
 *      true pole with respect to the mean pole.
 *
 *      all coeffieients are from Exp. Supp. pp.44-45
 */

        mnom = 296.104608 + 13.0649924465*eday + 9.192e-3*capt2
                 + 14.38e-6*capt3;
        mnom *= radian;
        msun = 358.475833 + .9856002669*eday - .150e-3*capt2
                 - 3.33e-6*capt3;
        msun *= radian;
        noded = 11.250889 + 13.2293504490*eday - 3.211e-3*capt2
                 - 0.33e-6*capt3;
        noded *= radian;
        dmoon = 350.737486 + 12.1907491914*eday - 1.436e-3*capt2
                 + 1.89e-6*capt3;
        dmoon *= radian;
        node = 259.183275 - .0529539222*eday + 2.078e-3*capt2
                 + 2.22e-6*capt3;
        node *= radian;

/*
 *      long period terms
 */

        phi = 0.;
        eps = 0.;
        dphi = 0.;
        deps = 0.;


        icosadd(nutfp, nutcp);
        phi = -(17.2327+.01737*capt)*sin(node);
        phi += sinadd(4, node, noded, dmoon, msun);

        eps = cosadd(4, node, noded, dmoon, msun);

/*
 *      short period terms
 */


        dphi = sinadd(4, node, noded, mnom, dmoon);

        deps = cosadd(3, node, noded, mnom);

        phi = (phi+dphi)*radsec;
        eps = (eps+deps)*radsec;
        dphi *= radsec;
        deps *= radsec;

        obliq = 23.452294 - .0130125*capt - 1.64e-6*capt2
                 + 0.503e-6*capt3;
        obliq *= radian;
        tobliq = obliq + eps;

        gst = 99.690983 + 360.9856473354*eday + .000387*capt2;
        gst -= 180.;
        gst = fmod(gst, 360.);
        if(gst < 0.)
                gst += 360.;
        gst *= radian;
        gst += phi*cos(obliq);
}