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WebSVN – planix.SVN – Blame – /os/branches/feature_unix/sys/src/cmd/astro/nutate.c – Rev 2

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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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}