The functions parameters are: gjd - geocentric JD based on UTC ra - right ascension (J2000) de - declination The function returns heliocentric correction helcor. Using helcor, you can computed Heliocentric JD from Geocentric JD. The relation is: HJD = GJD + helcor. We do not compute Barycentric JD (BJD).

gistfile1.php

function computeHELCOR($gjd, $ra, $de) {
//  $eps=23.45*Pi()/180;

	$ra = EREgI_Replace(" ", "", $ra);
	$de = EREgI_Replace(" ", "", $de);
	$ra_hh = IntVal(substr($ra, 0, 2));
	$ra_mm = IntVal(substr($ra, 2, 2));
	$ra_vv = DoubleVal(substr($ra, 4, 4));
	$de_dd = IntVal(substr($de, 0, 3));
	$de_mm = IntVal(substr($de, 3, 2));
	$de_ss = DoubleVal(substr($de, 5, 4));
	$prevod = DoubleVal(57.29577951);
	$eps = DoubleVal(0.408988821);
	$ra_mm /= 60;
  	$ra_ss /= 3600;
  	$ra_hh = $ra_hh + $ra_mm + $ra_ss;	
	$d_ra_hh = 15*$ra_hh;	// RA in degrees
  	$alfa = Deg2Rad($d_ra_hh);    // RA in rads
	$de_mm /= 60;
	$de_ss /= 3600;
  	$de_dd = $de_dd + $de_mm + $de_ss;	// DE in degrees
  	$delta = Deg2Rad($de_dd); // DE in rads

       $ra=$alfa;
       $de=$delta;
       if (abs(cos($de))<0.0000000001) {
	     if (sin($de)>0.0) { $de=Pi()/2-0.000000001; }
	     else { $de=-Pi()/2+0.000000001; }
	}
       if (abs(cos($ra))<0.0000000001) $ra=Pi()/2+0.0000000001;
       $sinbeta=cos($eps)*sin($de)-sin($eps)*cos($de)*sin($ra);

	$tanlam=(sin($de)*sin($eps)+cos($de)*cos($eps)*sin($ra))/(cos($de)*cos($ra));
       if ($sinbeta<1.0) $cosbeta=sqrt(1-$sinbeta*$sinbeta);
           else $cosbeta=0.0000000001;
       $coslam=cos($de)*cos($ra)/$cosbeta;
       $lam=atan($tanlam);
       if ($coslam<0) $lam=$lam+pi();
       if ($lam<0) $lam=$lam+2*pi();
       $tanbeta=$sinbeta/$cosbeta;
       $bet=atan($tanbeta);

	if ($gjd > 2400000) { 
		$t = $gjd - 2400000;
	} else { 
		$t = $gjd; 
	}
       $t=-51545.0+$t;
       $tt=1+$t/36525.0;
       $ls=(0.779072+0.00273790931*$t)*2*pi();
       $ms=(0.993126+0.00273777850*$t)*2*pi();
       $lm=(0.606434+0.03660110129*$t)*2*pi();
       $m2=(0.140023+0.00445036173*$t)*2*pi();
       $m4=(0.053856+0.00145561327*$t)*2*pi();
       $m5=(0.056531+0.00023080893*$t)*2*pi();

       $lams=$ls/Pi()*180*3600+6910.0*sin($ms)+72.0*sin(2*$ms)
             -17.0*$tt*sin($ms)
             -7*cos($ms-$m5)
             +6*sin($lm-$ls)+5*sin(4*$ms-8*$m4+3*$m5)
             -5*cos(2*$ms-2*$m2)-4*sin($ms-$m2)
             +4*cos(4*$ms-8*$m4+3*$m5)+3*sin(2*$ms-2*$m2)
             -3*sin($m5)-3*sin(2*$ms-2*$m5);
       $r=1.00014-0.01675*cos($ms)-0.00014*cos(2*$ms);

       $lams=$lams*pi()/(3600*180);
       $helcor=-0.00577552*$r*cos($bet)*cos($lam-$lams);

	return Sprintf("%.5f", $helcor);
}

Hello Hanno!

Have you tested if this function works ok with a big amount of test cases?
I'm working on an astronomical tool to help an Observatory compute their observation, and i've been searching for a complete heliocentric correction procedure like this one.
It's OK to you if I take this one and make it part of our tool?

Thanks!