public static function Gst00a($uta, $utb, $tta, $ttb) {
    $gmst00;
    $ee00a;
    $gst;

    $gmst00 = IAU::Gmst00($uta, $utb, $tta, $ttb);
    $ee00a  = IAU::Ee00a($tta, $ttb);
    $gst    = IAU::Anp($gmst00 + $ee00a);

    return $gst;
  }