What is the origin of autumn?

Autumn is divided into traditional solar terms. In China, traditionally, the "beginning of autumn" with 24 solar terms is regarded as the starting point of autumn and ends at the beginning of winter. At present, the division of the four seasons in China is often based on the change of temperature, which is based on the division of "climate average temperature" by modern scholar Zhang Bao. According to the weather average temperature method, there are two main criteria to judge autumn. First, the average daily temperature for five consecutive days 10℃-22℃ can be regarded as autumn and become a "short mark"; Second, the moving average temperature of five consecutive groups is lower than 22℃. A set of moving average temperatures refers to the average temperature of the day plus the average temperature of the previous four days divided by 5 to get the moving average temperature of five days, which is a "sliding scale". Entering autumn means that the hot weather has passed and it is beginning to cool down.

The main meteorological disasters in autumn are: autumn rain in West China, cold dew wind in the south, frost and chilling injury at low temperature. In autumn, the direct point of the sun gradually moves south from the northern hemisphere, passes through the equator after the autumnal equinox, and the sun directly shines in the southern hemisphere. Seen from the northern hemisphere, the angle of the sun gradually becomes lower, and the gap between day and night becomes smaller. At the autumnal equinox, the length of day and night is equal. In autumn, the distance between the earth and the sun is from far to near. Seen from the ecliptic plane, the sun is on the background of Leo, Virgo and Libra.