function yige_constellation($month, $day) {
 // 检查参数有效性
 if ($month < 1 || $month > 12 || $day < 1 || $day > 31) return false;

 // 星座名称以及开始日期
 $constellations = array(
  array( "20" => "宝瓶座"),
  array( "19" => "双鱼座"),
  array( "21" => "白羊座"),
  array( "20" => "金牛座"),
  array( "21" => "双子座"),
  array( "22" => "巨蟹座"),
  array( "23" => "狮子座"),
  array( "23" => "处女座"),
  array( "23" => "天秤座"),
  array( "24" => "天蝎座"),
  array( "22" => "射手座"),
  array( "22" => "摩羯座")
 );

 list($constellation_start, $constellation_name) = each($constellations[(int)$month-1]);

 if ($day < $constellation_start) list($constellation_start, $constellation_name) = each($constellations[($month -2 < 0) ? $month = 11: $month -= 2]);

 return $constellation_name;
}

echo yige_constellation(4, 20);