From the summer solstice, according to the arrangement of the dry and branch days, the third Geng day is the first day. The fourth Geng Day is the middling, and the first Geng Day after beginning of autumn is the last one. The word "Geng" in Gengri is the seventh word in the ten days of "A, B, C, D, E, Ji, G, Xin, Ren and Gui", and Gengri is repeated every ten days.
When is the "Third Geng Day"? There is no such date in the current calendar. In ancient China, the years, months, days and hours were all represented by the words "heavenly stems and earthly branches" (60 jiazi), so a person's birth time can be represented by "eight characters". Because there is no corresponding relationship between the date of "Geng Day" and the solar calendar, the start and end time of the dog days are different every year, which is roughly from mid-July to mid-August.
That is to say, after the Slight Summer Festival, beginning of autumn entered the final stage. Because the final lodging must be after beginning of autumn, and the initial lodging may be earlier or later, it may be 10 days or 20 days. To put it simply, when you enter the early stage, you usually enter the early stage before July 18 in the solar calendar, and the middle stage is 20 days, otherwise it is 10 days.
The summer solstice in 20 19 is June 2 1 day, which is the ugly day. The next day is Geng Yin Day, which is the first Geng Day after the summer solstice. Ten days are a round, the second Geng Day is July 2, and the third Geng Day is July 12, which is the first night.