24 절후 (節侯)의 16 번째로, 춘분 (春分)처럼 낮과 밤의 길이가 같은 날. 양력으로 9월 20일 경

The autumnal equinox day of the year: It falls around the twentieth day of September by the solar calendar. As it is with the spring equinox day, it is the day when the lengths of the daylight and night are equal.