Why is the great cold the shortest day in a year?

The Great Cold is the last of the 24 solar terms, and it is called "Great Cold" every year when the sun reaches 300 degrees on June 20-2 1 day of the Gregorian calendar. Quoting "San Li Yi Zong" and "Shi Tong Kao Tian" explains: "Great cold is the middle, and the upper form is slight cold, so it is called great cold ... extremely cold, so it is called great cold."

It is said that a cold is a cold. During the period of March 9 and April 9, the cold wave frequently goes south, which is the coldest season of the year and the period with the least rain. There is a folk saying that "a slight cold is the most important thing, and it is cold without wind." Great cold refers to extremely cold weather. This is a season where vitality lurks and everything is hidden.

Meteorological changes of severe cold solar terms

During the severe cold solar term, the atmospheric circulation is relatively stable, and the adjustment period of circulation is about 20 days. When this circulation is adjusted, there will often be a wide range of rain and snow weather and strong winds to cool down.

When the west of 80 degrees east longitude is a long wave ridge and East Asia is a coastal trough, under the influence of the northwest wind and the constantly supplemented cold air, China will have a sustained low temperature. In some parts of China, severe cold is not as cold as slight cold, but in the southern coastal areas of China, the lowest temperature in a year appears in the severe cold solar terms. ?

Refer to the above? Baidu encyclopedia-great cold