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- #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);
- }
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