ref: 4821c261c4cea895ddcbd7c70bc71103c9a2763b
dir: /sys/src/cmd/astro/helio.c/
#include "astro.h" void helio(void) { /* * uses lambda, beta, rad, motion * sets alpha, delta, rp */ /* * helio converts from ecliptic heliocentric coordinates * referred to the mean equinox of date * to equatorial geocentric coordinates referred to * the true equator and equinox */ double xmp, ymp, zmp; double beta2; /* * compute geocentric distance of object and * compute light-time correction (i.i. planetary aberration) */ xmp = rad*cos(beta)*cos(lambda); ymp = rad*cos(beta)*sin(lambda); zmp = rad*sin(beta); rp = sqrt((xmp+xms)*(xmp+xms) + (ymp+yms)*(ymp+yms) + (zmp+zms)*(zmp+zms)); lmb2 = lambda - .0057756e0*rp*motion; xmp = rad*cos(beta)*cos(lmb2); ymp = rad*cos(beta)*sin(lmb2); zmp = rad*sin(beta); /* * compute annual parallax from the position of the sun */ xmp += xms; ymp += yms; zmp += zms; rp = sqrt(xmp*xmp + ymp*ymp + zmp*zmp); /* * compute annual (i.e. stellar) aberration * from the orbital velocity of the earth * (by an incorrect method) */ xmp -= xdot*rp; ymp -= ydot*rp; zmp -= zdot*rp; /* * perform the nutation and so convert from the mean * equator and equinox to the true */ lmb2 = atan2(ymp, xmp); beta2 = atan2(zmp, sqrt(xmp*xmp+ymp*ymp)); lmb2 += phi; /* * change to equatorial coordinates */ xmp = rp*cos(lmb2)*cos(beta2); ymp = rp*(sin(lmb2)*cos(beta2)*cos(tobliq) - sin(tobliq)*sin(beta2)); zmp = rp*(sin(lmb2)*cos(beta2)*sin(tobliq) + cos(tobliq)*sin(beta2)); alpha = atan2(ymp, xmp); delta = atan2(zmp, sqrt(xmp*xmp+ymp*ymp)); hp = 8.794e0*radsec/rp; semi /= rp; if(rad > 0 && rad < 2.e5) mag += 2.17*log(rad*rp); }