public static function schoolYearAtTime($year = null) {
		static::loadData();
		if (is_null($year)) return static::schoolYear();
		foreach(static::$arrDBCalendar as $sy) {
			//return graduation year of current school year if available
			if($sy['start'] < $year && $sy['end'] > $year) return date('Y',$sy['end']);
			//else - if a school year is found which begins later than now but already in the current calendar year, return the end year
			//-> summer holidays := following school year
			elseif($sy['start'] > $year && date('Y',$sy['start']) == date('Y')) return date('Y',$sy['end']);
		}
		return false;
	}