ref: ac98922f44c3df8839f1bdd07f23fcccf27d0cba
dir: /sys/src/cmd/astro/sat.c/
#include "astro.h" void sat(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; ecc = .0558900 - .000347*capt; incl = 2.49256 - .0044*capt; node = 112.78364 + .87306*capt; argp = 91.08897 + 1.95917*capt; mrad = 9.538843; anom = 175.47630 + .03345972*eday - .56527*capt; motion = 120.4550/3600.; 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(); }