Cold dew is the seventeenth solar term in the twenty-four solar terms of the lunar calendar, belonging to the fifth solar term in autumn, which indicates the official end of the autumn season; The time is1October 7-9, 10 every year. When the sun reaches 195. "Twenty-four solar terms" said: "In September, the dew is cold and will condense." Cold dew means that the temperature is lower than that of the white dew, and the dew on the ground is colder and will soon condense into frost. In the cold dew season, Nanling and the vast area to the north have entered autumn, the northeast has entered late autumn, and the northwest has entered winter or is about to enter winter.

The temperature drops gradually. White dew, cold dew and first frost all indicate the phenomenon of water vapor condensation, and cold dew is the transition from cold to cold. At night, looking up at the starry sky, you will find that the season of the starry sky changes, and the "Big Mars" (Scorpio Antares), which represents the midsummer, has set in the west. We can vaguely hear the footsteps in winter.

At this time, the temperature in most parts of South China continued to drop. The average daily temperature in South China is less than 20℃. Even in the areas along the Yangtze River, it is difficult for the temperature to rise above 30℃, while the minimum temperature can drop below 10℃. Except for a few valley lowlands, the five-day average temperature in the northwest plateau is generally lower than 10℃, which is already winter according to the standard of four seasons climate division. First frost store, a thousand miles away, is quite different from the autumn scenery in South China.