The traditional Chinese calendar divides a year into 24 solar terms. Qiūfēn (pīnyīn), literally "Autumnal Equinox", is the 16th solar term. It begins when the Sun reaches the celestial longitude of 180° and ends when it reaches the longitude of 195°. It more often refers in particular to the day when the Sun is exactly at the celestial longitude of 180°, which in the Gregorian calendar is around September 23.

Each solar term can be divided into 3 pentads. They are: first pentad, second pentad and last pentad. Pentads in Qiufen include.

First pentad: Thunder begins to soften

Second pentad: Insects make nests

Last pentad: Water begins to solidify

"It is on the Autumn Equinox day that the Yin and Yang are in a balance of power. Thus the day and night are of equal length, and so are the cold and hot weather."