1. Autumn Equinox Definition: One of the twenty-four solar terms in the lunar calendar, it means the official entry of autumn.

2. Autumnal equinox is the sixteenth solar term among the twenty-four solar terms. It usually falls between September 22nd and 24th in the Gregorian calendar every year. On the autumnal equinox, the sun reaches 180° of ecliptic longitude (the autumnal equinox point), almost directly hitting the earth's equator, and day and night are of equal length in all parts of the world (regardless of the refraction of sunlight by the atmosphere and the morning and evening shadows). In ancient times, there was a saying that "spring offers sacrifices to the sun and autumn offers sacrifices to the moon." The autumnal equinox was once a traditional "moon sacrifice festival." The Mid-Autumn Festival in 2019 comes from the traditional "Moon Festival".

3. After the autumnal equinox, the direct point of the sun continues to move from the equator to the southern hemisphere, and the days begin to become shorter and the nights become longer in various parts of the northern hemisphere, that is, the days begin to be shorter than the nights in one day; the opposite is true in the southern hemisphere. Therefore, the autumnal equinox is also called the descending equinox. At the North and South Poles, on the autumnal equinox, the sun is above the horizon all day long. After that, as the sun's direct point continues to move southward, a six-month polar night begins near the North Pole, and the range gradually expands and then shrinks; a six-month polar day begins near the South Pole, and the range gradually expands and then shrinks.

4. On June 21, 2018, the State Council approved the establishment of the "Chinese Farmers' Harvest Festival" and agreed to establish the annual autumnal equinox as the "Chinese Farmers' Harvest Festival" starting from 2018.