How is the time of winter solstice determined?

The direct point of the sun moves southward to the extreme. On this day, the sun shines directly on the Tropic of Capricorn (23 26' s), and the sun is most inclined to the northern hemisphere, with the smallest elevation angle, which is the shortest day and the longest night in all parts of the northern hemisphere. The solstice in winter is also the turning point of direct sunlight returning to the north. After this day, it went back, and the direct sunlight began to move northward from the Tropic of Capricorn, and the northern hemisphere (China is located in the northern hemisphere) increased day by day.

Although the days from winter solstice in the northern hemisphere are short, the temperature from winter solstice is not the lowest; It won't be very cold before the winter solstice, because there is still accumulated heat on the surface, and the real winter is after the winter solstice; Because of the great differences in climate in different parts of China, the climatic characteristics in the sense of astronomy and meteorology are obviously late for most parts of China.

Meteorological change

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". On the day of "March 9 and April 9", the accumulated heat is the least, the temperature is the lowest, and the weather is getting colder and colder.

China has a vast territory, and the climate and landforms vary greatly from place to place. Although the days from winter solstice are short, the temperature from winter solstice is not the lowest; It won't be very cold before the winter solstice, because there is still "accumulated heat" on the surface, and the real cold winter is after the winter solstice. Due to the great differences in climate in different parts of China, the climatic characteristics of this day are obviously late for most parts of China.