protected function getYear() {
    $year = 0;
    if ($this->type == YearType::Besselian())
      $year = 1900 + ($this->jd - Epoch::B1900()->jd) / static::DaysBesselianYear;
    else
      $year = 2000 + ($this->jd - Epoch::J2000()->jd) / static::DaysJulianYear;

    return round($year, 6);
  }