When did the heat start? Why sometimes one is in the middle and sometimes two?

According to the climatic law of the lunar calendar in China, predecessors have long stipulated: "The third Geng day after long summer is the first day, the fourth Geng day is the second, and the first Geng day after beginning of autumn is the last (summer). Ten days at the beginning and end, ten or twenty days in the middle, and thirty or forty days in summer. " . Every year, if Geng Day falls on beginning of autumn Day and two days later, it is ten days in midsummer, otherwise it is twenty days. Therefore, the summer in most years is twenty days, and correspondingly, the summer in most years is forty days.

Because the third and fourth Geng days are the first days of initial lodging and intermediate lodging, and the interval between each Geng day is 10 day, the initial lodging time is 10 day, and the final lodging rule is 10 day. Summer is long and short, which may be 10 days or 20 days. If there is a Geng day in beginning of autumn and the next two days, it is 65,438+00 days, otherwise it is 20 days, so there is a difference of 30 days in some years and 40 days in some years.

The so-called "Summer Day" refers to the first, middle and last three days, and its specific date is calculated according to the ancient China dry branch method. In the twenty-four solar terms of the China lunar calendar, the third day after the summer solstice is the first day, and the first day after the beginning of autumn is the last day.