How is the date of the first volt determined?

"Dog days" is the general name of the first, middle and last three days, and it is the hottest season in a year. It appears from mid-July to mid-August in the solar calendar every year. Its climate is characterized by high temperature, low pressure, high humidity and low wind speed. "V" means being forced to hide underground. According to the climate law of the lunar calendar in China, it has long been stipulated by predecessors: "The third Geng day after long summer begins with the first day (the first day), the fourth Geng day is the middle day (the second day), and the first Geng day after beginning of autumn ends with the first and last ten days, the middle ten or twenty days, and the" third day "is * * thirty or forty days.

The specific date of the dog days is determined by the solar term date and the dry branch date. According to the traditional calculation method in China, the third and fourth Geng days from summer to the future are the start dates of the first (recumbent) and the second (recumbent) respectively, and the first Geng day after beginning of autumn is the first day of the last (recumbent). Gengri is an auspicious day with the word "Geng", such as Gengzi, Gengyin and Chen Geng ... such dates are published in rural yearbooks every year.

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. The incubation time is long or short, which may be 10 day or 20 days. Every year, the third Geng day after the summer solstice solar term appears in the morning and evening, so the number of days in the middle is different, so there is a difference of 30 days in some years and 40 days in some years.