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How was the first day of the first ambush calculated?

The time of accommodation is not fixed every year, and the length of accommodation is also different. You need to check the almanac to calculate it. Simply put, we can use the formula of "Xia San Geng" to express the lodging date, that is, from the third Geng day in Xia Hou, the initial lodging is 10 day, the intermediate lodging is 10 day or 20 days, and the final lodging is 10 day. In ancient China, the "trunk-branch calendar" was popular, and 60 groups of different names were used to record dates with 10 heavenly stems and 12 earthly branches, which were recycled. The day with the word "Geng" is called "Geng Day". The word "Geng" in Geng Day is the seventh word in "A, B, C, D, E, Ji, G, Xin, Ren, Gui" 10 day, and it is repeated every 10 day. Starting from the summer solstice, according to the date of trunk, the third Geng day is the first, the fourth Geng day is the middle, and the 1 th Geng day after beginning of autumn is the last. When there are four Geng days between the summer solstice and the beginning of autumn, the middle part is 10 days, and when there are five Geng days, the middle part is 20 days. It seems that the emergence of Gengri will affect the length of the first half sooner or later, so there will be 30 days in some years and 40 days in some years.

Picture of the dog days timetable in 2020

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Why do you say "the heat is at three volts"

After lodging, the surface humidity increases, and the heat absorbed every day is more, but the heat emitted is less, and the heat on the surface is accumulated. So it gets hotter every day, and when it enters the dog days, the accumulated heat on the ground reaches its peak and the weather is the hottest. In addition, there is much rain in summer, the air humidity is high, and the heat capacity of water is much greater than that of dry air, which is also an important reason for the sultry weather. The subtropical high intensified in July and August. Under the control of the subtropical high, the descending airflow inside the high makes the weather clear and cloudy, which is beneficial to the sunshine, the ground radiation heats up and the weather is hotter.

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Dog days are the best stage for people to keep fit. Chinese medicine believes that "summer heat and dampness should be clear". In hot summer, people like cold drinks and drink plenty of water, so that moisture invades the human body, while external moisture enters the body, making water wet and invigorating the spleen, lifting the spleen and stomach, causing digestive dysfunction, stagnant water and loss of appetite. Dampness in summer is very harmful to the spleen, and bitter food has the effect of purging dryness, so it is not advisable to eat more, so it is advisable to eat more sweet and cold or sweet and cold in daily diet. And summer returns to the heart, but the heart likes cold and should be sour, so eat more acidic food in summer.