sub _julianday{
	my ($day, $month, $year) = @_;
	my ($jd, $a, $y, $m) = ();
	
	if($year < 0){ $year++; }
	$a = (14 - $month)/12;
	$y = $year + 4800 - $a;
	$m = $month + 12 * $a - 3;

	# zunaechst gregorianisch rechnen, ist jd < 2299160 (4.10.1582), wird julianisch gerechnet 
	$jd = $day + ((153 * $m + 2)/5) + 365 * $y + ($y/4) - ($y/100) + ($y/400) - 32045;

	# hier wird julianisch gerechnet
	if( $jd < 2299160 ){
		$jd = $day + ((153 * $m +2)/5) + 365 * $y + ($y/4) - 32083;
	}

	return $jd;
}
sub _julianday_to_date{
	my $jd = shift;
	
	# Gregorian, common
	my $a = $jd + 32044;
	my $b = ( ( $a * 4 + 3)/146097);
	my $c = $a - (146097 * $b/4);
	my $gregorian = 1;

	# Pruefe auf Julian
	if($jd <= 2299160){
		$b = 0;
		$c = $jd + 32082;
		$gregorian = 0;
	}

	my $d = ((4 * $c + 3)/1461);
	my $e = $c - ((1461 * $d)/4);
	my $m = (($e * 5 + 2)/153);

	my $day = $e - ((153 * $m +2)/5) + 1;
	my $month = $m + 3 - ($m/10) * 12;
	my $year = 100 * $b + $d - 4800 + ($m/10);

	if($year < 0){ $year--; }
	if($year == 0){ $year = -1; }

	return ($day, $month, $year, $gregorian);	
}