White Dew is the 15th of the 24 Solar Terms, the third solar term in the fall, the end of the month of Shen and the beginning of the month of You in the Dry Branches Calendar. The sun reaches 165 degrees of the yellow meridian at the end of the month of Shen and the beginning of the month of You on the stem-chip calendar. "White Dew" is an important festival reflecting the growth of cold in nature. Due to the cold air to attack, daytime sunshine is still hot, but the evening after the temperature will soon fall, day and night temperature difference gradually widen.

Meteorological changes:

After entering the White Dew festival, summer winds are gradually replaced by winter winds, cold air south gradually frequent, coupled with the position of the sun directly above the ground southward, the northern hemisphere sunshine hours become shorter, sunshine intensity is weakened, the night is often clear, less cloudy, the ground radiation heat dissipation is fast, and therefore the temperature drop is also accelerated gradually, there are "White Dew Autumn Equinox Night, one night cool night" said.

After the White Dew, the temperature difference between day and night is gradually widening, the daytime temperature at noon is higher, but the morning and the night has been a slight coolness. According to modern scholars Zhang Bao Koon proposed "wait for the average temperature" division of the four seasons of the standard, wait for the average temperature of 10-22 ℃ during the spring or fall, according to this standard, from the White Dew Festival began, around the beginning of the fall.