How many days are there in the dog days of summer?

"Three volts" is the general name of the first, middle and last three volts, 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, predecessors have long stipulated: "The third Geng day from long summer to the future is the beginning, the fourth Geng day is the middle (second), and the first Geng day after beginning of autumn is the end (third), and the voltage is ten days * * thirty days." In some years, the "mid-crouch" is 20 days, while * * * is 40 days. 1, initial, intermediate and final voltages. The third Geng day after long summer is the first day of the first fall, the fourth Geng day is the first day of the middle fall, and the first Geng day after beginning of autumn is the first day of the last fall. The first fall and the last fall are each 10, and the middle fall is 10 or 20 days. Usually refers to a period of time from the first day of the initial stay to the tenth day of the final stay. Dog days are usually the hottest time of the year. 2. Specifically, according to the textual research of Yin-Yang calendar and Wanli calendar, we can know that the "three days" of the lunar calendar in 2005 AD are July 15, and the first ten days of the lunar calendar are the first days (also called the first days); July 25, the twentieth day of the lunar calendar, medium volt (two volts); /kloc-The last day of August (dog days) in 0/4 is the first day of July in the lunar calendar. Generally speaking, every volt is ten days and every volt is thirty days. However, the year of 2005 was "medium volt" (two volts) for twenty days. Therefore, the "dog days" period is forty days. That is, from the tenth day of the first lunar month to the last day (the twentieth day of the seventh lunar month), it is exactly forty days before and after. The "dog days" are determined according to the ancient "method of keeping records of the sun by the cadres and branches". Every summer to the future, the third Geng Day (referring to the day with the word "Geng" on the trunk and branches) is the beginning period, the fourth Geng Day is the middle period, and the first Geng Day after beginning of autumn is the end period, collectively referred to as the dog days. As the saying goes, "it's hot in dog days." According to the traditional calendar of our country, it is the hottest dog days in summer all year round. Three volts refers to three consecutive periods of initial, intermediate and final voltage. From summer to the future, the third Geng day is the first day of dive (today is the first day of dive this year), the fourth Geng day is the first day of dive, and the first Geng day after beginning of autumn is the first day of dive, each with 10 day, but in some years it is 20 days, such as 2005. Generally speaking, in the "dog days", the average temperature is the highest in the "middle range". Of course, this calculation method of the ancients is not very scientific, and it is not necessarily closely combined with the meteorological reality of that year. The extreme maximum temperature in all parts of the year does not necessarily appear in the "middle volt" or even in the "three volts". But in any case, "dog days" is indeed a hot summer time, and everyone should pay attention to heatstroke prevention and cooling. This name also introduces the day before the third Geng day from summer to the fourth Geng day. The third Geng Day was the first day of the first ambush. From the fourth Geng Day after midsummer to the first Geng Day after beginning of autumn. The fourth Geng day is the first day of mid-fu, and for beginning of autumn before July of the lunar calendar, mid-fu is 10 day; For the beginning of autumn season after July of the lunar calendar, midsummer is 20 days. A period of time from the first Geng Day after the last autumn in beginning of autumn to the day before the second Geng Day. The second Geng day is designated as going out, that is, the end of the dog days.