Hanlu means: exposure of cold air.

Cold means cold, which means the temperature has become significantly lower. Dew is dewdrops, dew. So cold dew is simply cold dew, cold dew. Dew is a natural phenomenon in which water vapor in the air condenses on surface objects when it is cold. It also refers to the water condensed under this condition. It seems simple, but the ancients used the common phenomenon of cold dew to represent changes in the natural climate.

Cold dew is the seventeenth solar term of the twenty-four solar terms and the fifth solar term in autumn. Dou Zhi Xin; the sun reaches 195° of the ecliptic longitude; the festival occurs between October 7 and 9 of the Gregorian calendar every year. Cold dew is the season of late autumn and the beginning of the Xu month in the calendar of the zodiac. Cold dew is a solar term that reflects the characteristics of climate change. Entering the cold dew, cold air sometimes moves southward, the temperature difference between day and night is large, and autumn dryness is obvious.

The historical origin of the cold dew

The cold dew is the end of the You month and the beginning of the Xu month in the Ganzhi calendar. At night, if you look up at the stars, you will find that the "big Mars" (Antarse), which represents midsummer, has set in the west. After the cold dew, the height of the sun continues to decrease and the temperature gradually drops. The temperature during Cold Dew and White Dew solar terms has dropped a lot, and the cold dew condenses, so it is called "Cold Dew". "Collection of the Seventy-Two Hours of the Moon Order" says: "On the Ninth Festival, the dew is cold and will condense." At this time, the temperature is lower than during the "White Dew" period, there is more dew, and it is chilly day and night.

In Chinese folk, there is a proverb that "the dew is white first and then cold", which means that after the white dew solar term, the dew changes from a cool feeling in early autumn to a "white dew desire" with a bit of coldness in late autumn. frost". There is also a proverb about cold dew: "After three dynasties of cold dew, you have to look for a bridge to cross the water." This means that the weather has become cold and you can't cross the river or go to the fields barefoot like before.

During the cold dew period, people can clearly feel the temperature difference. The change from pure white dew to cold and condensing water vividly reflects the continuous drop in temperature. As the cold air grows, everything becomes increasingly desolate.

The above content refers to Baidu Encyclopedia-Hanlu