What is the formula for counting nine days?

The formula for nine days is: 1929, not shooting, and on the ice in 3949. In 5969, I saw the willows by the river, in 79, I opened the river, and in 89, the geese came. 99 plus 19, plowing cattle everywhere.

There is a folk proverb in China that "the first nine days are warm, and the last nine days are cold". It turns out that if the first nine days are warm, the next winter will be particularly cold. Since March 9, it has entered the coldest stage of freezing.

But in fact, April 9 is the coldest time in winter. It was only a few days before March 9 that the temperature changed greatly, and suddenly it became cold, so the body did not adapt, so it was particularly cold. By April 9, the temperature was lower than that on March 9, but the temperature difference changed little, and it didn't feel as cold as when it entered March 9.

Extended data

During the winter solstice, the northern hemisphere receives the least solar radiation, which is 50% less than that of the southern hemisphere. There are only nine hours in Beijing during the day. But this day is the ninth day, not the coldest time, because there is atmosphere and water on the surface of the earth, which can store heat, not "save or lose" but "accumulate heat"

After the winter solstice, although the altitude angle of the sun gradually rises, the recovery process is slow, 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 temperature is the least, the temperature is the lowest, and the weather is getting colder and colder.

If there is cold air at this time, the weather will be colder. After this "cold front", the weather will gradually get warmer. Therefore, "March 9 is cold" and "September 9" have been in the summer calendar 1 and February, and most parts of China have entered spring, so "September 9 is sunny".