/**
* Finds the accurate time of a solstice or equinox using the complete VSOP87
* theory
*
* @param int $year The year to find a solstice or equinox for
* @param array $terms An array of the mean terms for the desired equinox or
* solstice
* @param int $month The month of the equinox or solstice to find
*
* @return float The JD of the solstice or equinox in TD
*/
private static function accurate($year, array $terms, $month)
{
$Y = $year < 1000 ? (int) $year / 1000 : ((int) $year - 2000) / 1000;
$q = intval($month / 3) - 1;
$jde0 = static::Horner($Y, $terms);
for ($i = 0; $i < 100; $i++) {
// TODO:: use vsop 87, but use IAU apparent stuff?
$λ = Solar::ApparentEclVSOP87(AstroDate::fromJD($jde0))->λ->rad;
$Δ = 58 * sin(deg2rad($q * 90) - $λ);
$jde0 += $Δ;
if (abs($Δ) < 5.0E-7) {
break;
}
}
return $jde0;
}
