What is the meaning of "three Geng and three volts in summer and nine volts in winter"?

"The solstice in summer is the third watch, and the solstice in winter is the ninth watch." This means that the solstice enters the third Geng day after the early summer and the first Ren day after the solstice enters beginning of winter. As for Gengri and Renri, this is the trunk and branch timing method in the ancient calendar. For example, the third night in summer refers to the third day after the summer in Gengshen, Wu Geng and Chen Geng, and Chen Geng Day is the third night, which is the beginning of several volts. The winter solstice is the first day after the winter solstice, when there is a "non-alliance". For example, Ren Xuri has a non-union day on the winter solstice, which is the beginning of counting nine.

Our ancestors were clever. That is, at that time, ancestors knew that the low temperature in winter had little influence on the humidity change, which made the influence on the human sensory temperature negligible, so the count of nine began from the winter solstice. Because of the high temperature in summer, the influence on air humidity is particularly obvious, which makes the influence of humidity on human body's perceived temperature not be ignored. The dry air in spring, even in the summer solstice, has not decreased, resulting in the summer solstice air is still relatively dry, suitable for human body surface to emit heat, so the human body feels that the temperature is not the highest. However, between midsummer and hot summer, the humid air will be menacing, and the human body will feel that the temperature will rise linearly and even sweat, so the number of volts does not start from the summer solstice. The dog days begin from summer to the third Geng day in the future; The beginning of nine days is counted from the day of winter solstice. Because the third Geng Day after long summer is inconsistent with the solar calendar, the dog days are different every year, while the dog days or nine days are fixed.

The dog days include the first, middle and last days. The third Geng day after the summer solstice is the beginning, the fourth Geng day is the middle, and the first Geng day after beginning of autumn is the end. The first and last days are 10 days, and the intermediate days are not fixed. Some years are 10 days, and some years are 20 days. The fifth Geng Day from summer to the future is the first 20 days in beginning of autumn.

The calculation of dog days is not only related to the 24 solar terms, but also depends on the branch year. These are all things handed down from our ancestors, which are worth learning and understanding. Young people should not throw them away, but should continue to pass them on. What do you think of this?