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87 lines
1.7 KiB
C
87 lines
1.7 KiB
C
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#include "astro.h"
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void
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nutate(void)
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{
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/*
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* uses radian, radsec
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* sets phi, eps, dphi, deps, obliq, gst, tobliq
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*/
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double msun, mnom, noded, dmoon;
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/*
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* nutation of the equinoxes is a wobble of the pole
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* of the earths rotation whose magnitude is about
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* 9 seconds of arc and whose period is about 18.6 years.
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*
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* it depends upon the pull of the sun and moon on the
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* equatorial bulge of the earth.
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*
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* phi and eps are the two angles which specify the
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* true pole with respect to the mean pole.
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*
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* all coeffieients are from Exp. Supp. pp.44-45
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*/
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mnom = 296.104608 + 13.0649924465*eday + 9.192e-3*capt2
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+ 14.38e-6*capt3;
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mnom *= radian;
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msun = 358.475833 + .9856002669*eday - .150e-3*capt2
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- 3.33e-6*capt3;
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msun *= radian;
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noded = 11.250889 + 13.2293504490*eday - 3.211e-3*capt2
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- 0.33e-6*capt3;
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noded *= radian;
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dmoon = 350.737486 + 12.1907491914*eday - 1.436e-3*capt2
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+ 1.89e-6*capt3;
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dmoon *= radian;
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node = 259.183275 - .0529539222*eday + 2.078e-3*capt2
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+ 2.22e-6*capt3;
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node *= radian;
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/*
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* long period terms
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*/
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phi = 0.;
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eps = 0.;
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dphi = 0.;
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deps = 0.;
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icosadd(nutfp, nutcp);
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phi = -(17.2327+.01737*capt)*sin(node);
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phi += sinadd(4, node, noded, dmoon, msun);
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eps = cosadd(4, node, noded, dmoon, msun);
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/*
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* short period terms
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*/
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dphi = sinadd(4, node, noded, mnom, dmoon);
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deps = cosadd(3, node, noded, mnom);
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phi = (phi+dphi)*radsec;
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eps = (eps+deps)*radsec;
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dphi *= radsec;
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deps *= radsec;
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obliq = 23.452294 - .0130125*capt - 1.64e-6*capt2
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+ 0.503e-6*capt3;
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obliq *= radian;
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tobliq = obliq + eps;
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gst = 99.690983 + 360.9856473354*eday + .000387*capt2;
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gst -= 180.;
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gst = fmod(gst, 360.);
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if(gst < 0.)
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gst += 360.;
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gst *= radian;
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gst += phi*cos(obliq);
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}
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