| #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); |
| } |
