129 lines
2.5 KiB
C
129 lines
2.5 KiB
C
#include "astro.h"
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void
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sat(void)
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{
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double pturbl, pturbb, pturbr;
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double lograd;
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double dele, enom, vnom, nd, sl;
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double capj, capn, eye, comg, omg;
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double sb, su, cu, u, b, up;
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double sd, ca, sa;
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ecc = .0558900 - .000347*capt;
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incl = 2.49256 - .0044*capt;
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node = 112.78364 + .87306*capt;
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argp = 91.08897 + 1.95917*capt;
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mrad = 9.538843;
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anom = 175.47630 + .03345972*eday - .56527*capt;
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motion = 120.4550/3600.;
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incl *= radian;
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node *= radian;
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argp *= radian;
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anom = fmod(anom, 360.)*radian;
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enom = anom + ecc*sin(anom);
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do {
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dele = (anom - enom + ecc * sin(enom)) /
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(1. - ecc*cos(enom));
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enom += dele;
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} while(fabs(dele) > converge);
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vnom = 2.*atan2(sqrt((1.+ecc)/(1.-ecc))*sin(enom/2.),
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cos(enom/2.));
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rad = mrad*(1. - ecc*cos(enom));
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lambda = vnom + argp;
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pturbl = 0.;
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lambda += pturbl*radsec;
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pturbb = 0.;
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pturbr = 0.;
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/*
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* reduce to the ecliptic
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*/
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nd = lambda - node;
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lambda = node + atan2(sin(nd)*cos(incl),cos(nd));
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sl = sin(incl)*sin(nd) + pturbb*radsec;
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beta = atan2(sl, pyth(sl));
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lograd = pturbr*2.30258509;
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rad *= 1. + lograd;
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lambda -= 1185.*radsec;
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beta -= 51.*radsec;
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motion *= radian*mrad*mrad/(rad*rad);
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semi = 83.33;
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/*
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* here begins the computation of magnitude
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* first find the geocentric equatorial coordinates of Saturn
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*/
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sd = rad*(cos(beta)*sin(lambda)*sin(obliq) +
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sin(beta)*cos(obliq));
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sa = rad*(cos(beta)*sin(lambda)*cos(obliq) -
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sin(beta)*sin(obliq));
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ca = rad*cos(beta)*cos(lambda);
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sd += zms;
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sa += yms;
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ca += xms;
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alpha = atan2(sa,ca);
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delta = atan2(sd,sqrt(sa*sa+ca*ca));
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/*
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* here are the necessary elements of Saturn's rings
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* cf. Exp. Supp. p. 363ff.
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*/
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capj = 6.9056 - 0.4322*capt;
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capn = 126.3615 + 3.9894*capt + 0.2403*capt2;
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eye = 28.0743 - 0.0128*capt;
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comg = 168.1179 + 1.3936*capt;
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omg = 42.9236 - 2.7390*capt - 0.2344*capt2;
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capj *= radian;
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capn *= radian;
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eye *= radian;
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comg *= radian;
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omg *= radian;
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/*
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* now find saturnicentric ring-plane coords of the earth
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*/
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sb = sin(capj)*cos(delta)*sin(alpha-capn) -
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cos(capj)*sin(delta);
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su = cos(capj)*cos(delta)*sin(alpha-capn) +
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sin(capj)*sin(delta);
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cu = cos(delta)*cos(alpha-capn);
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u = atan2(su,cu);
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b = atan2(sb,sqrt(su*su+cu*cu));
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/*
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* and then the saturnicentric ring-plane coords of the sun
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*/
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su = sin(eye)*sin(beta) +
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cos(eye)*cos(beta)*sin(lambda-comg);
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cu = cos(beta)*cos(lambda-comg);
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up = atan2(su,cu);
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/*
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* at last, the magnitude
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*/
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sb = sin(b);
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mag = -8.68 +2.52*fabs(up+omg-u)-
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2.60*fabs(sb) + 1.25*(sb*sb);
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helio();
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geo();
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}
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