What is the meaning of the Millennium in the twenty-four solar terms?

Millennium is the 15 solar term in the "twenty-four solar terms", and the third solar term in autumn is the end of the application of the moon in the lunar calendar and the beginning of the unitary month. When the sun reaches 165 degrees, it will cross the Gregorian calendar on September 7-9. "White dew" is an important solar term reflecting the growth of cold in nature. As the cold air turns to attack, it is sunny and hot during the day, but the temperature drops rapidly after the evening, and the temperature difference between day and night gradually widens.

Meteorological changes:

After entering the Millennium solar terms, the summer monsoon is gradually replaced by the winter monsoon, and the cold air gradually moves southward frequently. In addition, the position where the sun directly touches the ground moves south, and the sunshine time in the northern hemisphere becomes shorter and the sunshine intensity weakens. At night, it is often partly cloudy and sunny, and the ground radiation dissipates quickly, so the temperature drop is gradually accelerated. There is a saying called "Qiu Qiu in a thousand years, it is cold all night."

After the Millennium, the temperature difference between day and night gradually widened. Although the temperature is high at noon during the day, it is already very cold in the morning and at night. According to the standard of "average weather temperature" proposed by modern scholar Zhang Baokun, the average weather temperature is 10-22℃ in spring or autumn. According to this standard, from the beginning of the Millennium solar term, all localities began to enter autumn one after another.