The Chinese lunar calendar is based on the cycle of moon phases, with each cycle of new moon to full moon representing a month. It also takes into account the solar year to determine the length of a year. The 24 Solar Terms and leap months are set to align the average lunar year with the solar year. The 24 Solar Terms in the lunar calendar are determined by the Earth's position on the ecliptic, reflecting changes in seasons. They were important strategies for agricultural production during China's agrarian society and served as an essential reference for predicting climate changes such as temperature, rain, and snow in daily life.
The 24 Solar Terms include: Start of Spring, Rain Water, Awakening of Insects, Spring Equinox, Pure Brightness, Grain Rain, Start of Summer, Minor Fullness, Grain in Ear, Summer Solstice, Minor Heat, Major Heat, Start of Autumn, End of Heat, White Dew, Autumn Equinox, Cold Dew, Frost's Descent, Start of Winter, Minor Snow, Major Snow, Winter Solstice, Minor Cold, and Major Cold. White Dew is the fifteenth of the 24 Solar Terms, occurring when the sun reaches 165 degrees of ecliptic longitude, approximately 15 days after the End of Heat. It is the third solar term of autumn, generally occurring in early September on the Gregorian calendar. In 2019, the White Dew occurred on September 8th.

During the White Dew, dew can be seen, indicating that the cooling effect at night has become quite noticeable. This dew serves as a sign that the weather is beginning to turn cooler, signaling that the hot summer has passed and a cool autumn is coming. Of course, the climate around the time of White Dew usually features relatively cool mornings and evenings, while temperatures remain high at noon, resulting in a significant difference between day and night temperatures. At this time, the monsoons affecting China gradually shift from summer winds to winter winds, with cold air starting to move southward, leading to the phenomenon of "a fall rain brings a chill." In northern China, precipitation decreases significantly during this period, resulting in clear and pleasant weather, and temperatures begin to drop, causing migratory birds like geese to start moving toward warmer southern regions.
The arrival of the White Dew marks the entry into typical autumn weather, with cold air beginning to affect the region. Nights tend to be colder, and in agricultural practices, attention should be paid to keeping warm. Farmers may use irrigation to increase the soil's heat capacity to maintain warmth. For our bodies, the autumn season during the White Dew period can lead to dryness symptoms such as dry mouth and throat. Although the external climate begins to turn cool, our internal body remains hot. Therefore, the classic health care advice "don't dress too warmly in spring and don't wear too little in autumn" is essential for maintaining well-being.