The fourth solar term in autumn

The fourth solar term in autumn is the autumnal equinox.

It 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.

Historical origin:

Twenty-four solar terms: "See the vernal equinox in mid-August". "Divide" means to divide day and night equally. Like the vernal equinox, the sun shines directly at the equator of the earth, and day and night are equal. After that, the days became shorter and the nights became longer.

"Spring and Autumn Stories Yin and Yang in and out" said: "The autumn equinox, Yin and Yang are also half-phase, so it is cold and summer day and night." The autumnal equinox is just in the middle of 90 days in autumn, which means "equal share", so it is called "autumnal equinox".

The autumnal equinox used to be the traditional "Festival of Sacrificing the Moon". Now Mid-Autumn Festival comes from the traditional autumnal equinox "offering sacrifices to the moon". According to textual research, the Mid-Autumn Festival was originally set on the day of the autumnal equinox, but because this day is not always a full moon, the Mid-Autumn Festival was later transferred from the twenty-four solar terms of the autumnal equinox to the fifteenth day of the eighth lunar month.