When did it first appear?

Entering a crouching state means entering the dog days. "On the summer solstice, the head of the three gengzi falls", which is the basis for establishing the first autumn.

The so-called "dog days" refers to the days between the two solar terms of light summer and great summer, about between the middle and late July and the early August of the solar calendar. The dog days usually last for 30 to 40 days, which is the hottest, wettest and sultry day of the year. "Dog days" means "the heat in summer lurks underground" (it feels hot even if you think about it), so "dog days" represents the hottest period of the year.

"Sanfu" corresponds to "Sanjiu", and there is a popular saying among the people that "Sanjiu is cold, Sanjiu is hot" and "Three days in winter, Xia San is sunny".

What does it mean to "count people from the summer solstice in the third year"? In fact, it means that the third Geng day after "summer" begins to fall. In other words, the third Geng Day after long summer every year is the first day of the dog days of the solstice.

Because the third Geng day from summer to the future is not fixed every year (the same reason as "the birthday of the solar calendar is inconsistent with the birthday of the lunar calendar"), and the setting time of the sky is not fixed every year, many people are confused about when the "dog days" begin.

In addition, the lodging time varies from year to year (10 day or 20 days), so it cannot be simply calculated according to the algorithm of "one volt is 10 day" (the initial and final lodging are fixed at 10 day), so many people can't tell when the "dog days" will end.

① Before 10 days, after 10 days, and in the middle 10 days or 20 days; ② The third Geng day after "Summer" is the first lodging 1 day, and the first lodging is calculated from this day; (3) The first Geng Day after "beginning of autumn" is the first day of the last night, and the "dog days" will end on this day 10.