White Dew

Bailu is the 15th solar term in the "Twenty-Four Solar Terms", the third solar term in autumn, the end of the Shen month of the stem and branch calendar and the beginning of the You month. Dou refers to Gui; the sun reaches 165 degrees of the Yellow Longitude; the festival is on September 7-9 of the Gregorian calendar. "White Dew" is an important solar term reflecting the growth of cold air in nature. As the cold air turns from defense to attack, the sun is still hot during the day, but the temperature drops quickly after the evening, and the temperature difference between day and night gradually widens.

When it reaches the white dew, the summer monsoon is gradually replaced by the winter monsoon, and the cold air turns from defense to attack. In addition, the direct sunlight point moves to the south, the sunshine time in the northern hemisphere is shortened, the light intensity is weakened, and the radiation and heat dissipation on the ground are fast, so the temperature drop is gradually accelerated. . Bailu basically ended the sultry heat of the summer, the weather gradually turned cooler, and the cold was born. The ancients used the four seasons to match the five elements. Autumn belongs to gold, gold and white, and white is used to describe the autumn dew, hence the name "white dew".