The autumnal equinox is the sixteenth solar term among the twenty-four solar terms and the fourth solar term in autumn. Fight refers to unitary; The sun reaches the yellow meridian180; Celebrated on September 22-24 of the Gregorian calendar every year. On the day of the autumnal equinox, the sun shines almost directly on the equator of the earth, and the length of day and night is equal all over the world. The autumnal equinox means "equally divided" and "equally divided", which means equally dividing autumn except day and night. After the autumnal equinox, the position of direct sunlight moves south, and the days in the northern hemisphere become shorter, the nights become longer, the temperature difference between day and night increases, and the temperature drops day by day.

The autumnal equinox used to be the traditional "Moon Festival", and the Mid-Autumn Festival evolved from the "Autumn Moon Festival". On June 265438, 2065438, the State Council issued a reply on the establishment of "China Farmers' Harvest Festival", agreeing to establish the annual autumn equinox as "China Farmers' Harvest Festival" from 20 18.