What does the third phase of the Millennium solar terms mean?

The three stages of the Millennium solar term are: the arrival of geese, the return of mysterious birds and the shame of birds. The Millennium is the third solar term in autumn, in which the first class refers to the swan flying from north to south, the second class refers to the swallows flying south to avoid the cold, and the third class refers to the birds storing food for winter. There is a folk saying: "The white dew is the autumn night, and the geese fly south", "beginning of autumn wakes up, the sunflower laughs at the summer solstice, and the white dew returns to the geese, and the autumn equinox smells like osmanthus." Therefore, migratory birds like geese are regarded as a symbol of autumn.

The Millennium is an important solar term reflecting the growth of cold in nature. The ancients named it "Bailu" because the four seasons match the five elements, and autumn belongs to gold, and gold is white.

The White Dew is the watershed of the summer heat, and "White Dew" represents the end of the summer heat. After entering the Millennium solar terms, the summer monsoon is gradually replaced by the winter wind, and the cold air gradually moves south frequently. In addition, the position of the direct sunlight on the ground moves south, so 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 temperature drops gradually. Therefore, there is a saying that "a thousand years are divided into autumn nights, and one night is cold".

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. Starting from the Millennium solar terms, according to the standard of dividing the four seasons by climatology, all localities began to enter autumn one after another. At this time, the temperature difference between day and night in China can reach 8℃ to 16℃, so the Millennium is a solar term with a large temperature difference in a year.