$springEquinoxDay=(int)(20.8431 + 0.242194 * ( $year - 1980))
- (int)((double)($year - 1980)/4) ;
$springEquinox=array(3,$springEquinoxDay,"春分の日");
$automnEquinoxDay=(int)(23.2488 + 0.242194 * ( $year - 1980))
- (int)(($year - 1980)/ 4);
$automnEquinox=array(9,$automnEquinoxDay,"秋分の日");
$official_holidays=array( array(1,1,"元旦"),
array(2,11,"建国記念日"),
$springEquinox,
array(4,29,"昭和の日"),
array(5,3,"憲法記念日"),
array(5,4,"みどりの日"),
array(5,5,"こどもの日"),
$automnEquinox,
array(11,3,"文化の日"),
array(11,23,"勤労感謝の日"),
array(12,23,"天皇誕生日"));
春分の日・秋分の日の算出方法は、こちらを参照させていただきました。