public static function Obl80($date1, $date2) {
    $t;
    $eps0;

    /* Interval between fundamental epoch J2000.0 and given date (JC). */
    $t = (($date1 - DJ00) + $date2) / DJC;

    /* Mean obliquity of date. */
    $eps0 = DAS2R * (84381.448 +
            (-46.8150 +
            (-0.00059 +
            ( 0.001813) * $t) * $t) * $t);

    return $eps0;
  }