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