What is the winter solstice and 174?

"Yang dun zhong dong" and "Jing-Zhe 174" mean that in winter and Jing-Zhe, there is one Yang dun in Shangyuan, seven Yang dun in Zhongyuan and four Yang dun in Xiayuan.

According to the theory of twenty-four solar terms, each solar term is fifteen days, and one section is divided into three parts, namely, upper, middle and lower parts, each with three parts and five days.

On the day of winter solstice, the northern hemisphere gets the least solar radiation, about 50% less than the southern hemisphere. Beijing's daylight saving time is only over 9 hours. But this day is the first day of counting nine, and it is not the coldest time. This is because there is atmosphere and water vapor on the surface of the earth, which can store heat, not "save or lose" but "accumulate heat". From winter to the future, although the solar altitude angle gradually increases, it is a slow recovery process, and the heat lost every day is still greater than the heat received, showing a situation of "making ends meet". ?

In the "three or nine days", the accumulated heat is the least, the temperature is the lowest, and the weather is getting colder and colder. If there is the influence of cold air at this time, the weather will be even colder. After this "cold front", the weather will gradually get warmer. So it is said to be "cold in March", but "September 9" is already January and February in the summer calendar, and most parts of China have entered spring, so "September 9 is sunny".