Practice three or nine in winter and three volts in summer. The summer heat is not hot, but the summer heat is in the dog days. There is no rain, and the summer solstice is very hot. Wan Li is cloudless and sweltering in summer solstice. The summer solstice is full of thunder and drought.

Introduction to dog days:

The dog days, which appear between the summer heat and the summer heat, are the period with the highest temperature, the highest humidity and the most severe sultry heat in a year. Three volts can be divided into initial, middle and final volts, and its date is determined by the coordination of 24 solar terms and the dates of dry and branch. After "entering the volt", many places in the country will enter the continuous high temperature mode.

The traditional almanac stipulates that "counting from the third Geng day in summer", that is to say, "counting down from the summer day until the third Geng day" is about to begin to dormant. The "Geng Day" here refers to the days prefixed with "Geng" in the ancient "Ganzhi Jiri Law". "crouching" means being forced to hide underground; This also means that it is too hot to move.

The length of dog days mainly lies in the difference between middle and next days. Because the third Geng day (the first autumn) after the summer solstice solar term occurs at different times every year, the number of days in the middle autumn is also different. The incubation time is long or short, which may be 10 day or 20 days. So there are two situations: some years are 30 days in dog days, and some years are 40 days.

The dog days appear between the slight summer heat and the severe summer heat (from mid-July to mid-August in Gregorian calendar), and the dog days are divided into three days: the beginning, the middle and the end. Dog days are characterized by high temperature, low air pressure, high humidity and low wind speed. "crouching" means being forced to hide underground; This also means that it is too hot to move. The date of the dog days is determined by the coordination of 24 solar terms and the date of the main branch.

Because every Geng day is 10 days apart, the stipulated time of the first day and the last day is 10 days. Because the third Geng Day (the first autumn) after long summer appeared sooner or later, the days of autumn were long and short.

The dog days are the hottest, wettest and sultry time of the year. The reason why the air humidity is high in dog days is that the southeast wind blows in dog days, while the southeast is the ocean and the air is humid. The humidity of the sea breeze leads to the high humidity in dog days. In dog days, "high temperature and high humidity" is the climate characteristic of southern China.

The inland areas in the north are far from the ocean, and the climate is characterized by "high temperature and dryness". "Three volts" and "three summers" (summer, summer and midsummer in the 24 solar terms) both represent high temperature and extreme weather, and the curves on the time axis and the temperature axis are basically the same: summer comes, summer comes; When the sky falls, summer is over.

The reason why the ancients called the extremely hot day of the year "summer heat" and found a "fu" to accompany it, in addition to the cultural meaning, another important purpose is for health care.