ref: 2985d53b7a06d8a1712493aa899d6ffcfacd9e3b
dir: /sys/src/cmd/astro/nutate.c/
#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); }