Introduction and meaning of autumnal equinox.

1, the autumnal equinox, is the sixteenth of the twenty-four solar terms, and the time is generally from September 22nd to 24th of the Gregorian calendar every year. On the day of the autumnal equinox, the sun reaches the longitude 180 (autumnal equinox), almost reaching the equator of the earth, and the length of day and night is equal all over the world (regardless of the refraction of the sun light by the atmosphere and the shadow in the morning). In ancient times, there was a folk activity of "offering sacrifices to the sun in spring and the moon in autumn". The autumnal equinox used to be the traditional "Moon Festival" (Mid-Autumn Festival), which evolved from offering sacrifices to the moon in autumn.

The meaning of autumnal equinox is that day and night are equal. On this day, the sun reached the longitude 180 degrees, and directly hit the equator of the earth. Therefore, in most parts of the world, 24 hours are divided equally between day and night, each being 12 hours. After the autumnal equinox, the direct point of the sun began to enter the southern hemisphere from the equator, and the northern hemisphere began to have shorter days and longer nights, and the day began to be shorter than the night. Near the North Pole, there are long nights and stars for six months in a year.

The second meaning of autumnal equinox is that the climate changes from hot to cold. According to the division of seasons in ancient China, which started with beginning of spring, Changxia, beginning of autumn and beginning of winter, the autumnal equinox is divided into 90 days in autumn and divided equally in autumn.