"It's cold for nine days, but it's cold for three or nine days". "Sanjiu" usually appears from the winter solstice to the fright. "Sanjiu" refers to the third "nine days" after the winter solstice, that is, the 19th to 27th days after the winter solstice. "The third ninth day after the winter solstice" refers to "March 99", which is also the day when "March 99" and "April 99" intersect, not "March 99", that is, "March 99" is nine days instead of one day.

the calculation method is to count from the winter solstice in winter (starting from the winter solstice, it means the beginning of cold), and every nine days is a "nine", the first nine days are called "one nine", the second nine days are called "two nine", and so on, until "nine nine nine", that is, to the ninth nine days, counting up to 9981 days.

during the winter solstice, the daytime is the shortest, the angle between the direct sunlight and the ground is the smallest, and the sunshine intensity on the ground per unit area is the smallest, so the ground gets the least solar heat every day, and the daily heat budget deficit on the ground has not reached the maximum. After the winter solstice, although the daytime is growing day by day, the growth rate is very slow. From the winter solstice to the "March 9" period, the average daily growth is only about one minute. At the same time, the angle between the direct angle of the sun and the ground is also slowly increasing.

the daily heat budget of the ground is still in deficit, so it continues to lose heat and the ground temperature continues to drop. The deficit of total heat balance on the ground only reached its maximum in the "March 9th" season. Because the air temperature is mainly affected by the ground temperature, this leads to the lowest temperature in the "March 9th" season.

The earth absorbs the heat from the solar radiation during the day and gives it away at night. In summer, more heat is absorbed during the day and less heat is emitted at night, so that some heat can be accumulated every day. In winter, less heat is absorbed during the day and more heat is emitted at night. Not only can it not be accumulated every day, but it is also necessary to use some of the heat accumulated in summer. On the day of the winter solstice, less heat is absorbed during the day, but there is still some stored heat on the earth. After the winter solstice, less and less heat is stored. By March 9th, the earth's heat storage is the least in a year, so it is the coldest. Expanding information

There are many customs of "counting nine", among which "Jiujiu Song" is the most extensive and has a long history. These ballads skillfully use the phenological phenomena in nature and vividly reflect the law of weather change in the ninth five-year plan. As far as most areas in our country are concerned, the weather is not the coldest when the 29 th is over, but just "1929, I can't reach out." At the end of April 9th, it was almost the "Great Cold" solar term, so we said "March 9th, freezing cats and dogs".

After the May 9th, the earth gradually rejuvenated, and the weather turned from cold to warm, so "May 969, see the willows by the river; 7989, walking alone. " By 1999, it was already a "shock pad" solar term, so "the thunder in 1999 made a lasting noise."

the custom of "painting nine" appeared in the Ming dynasty. The so-called painting is actually a picture that calculates the date of spring warmth after the winter solstice. In the Ming Dynasty, "A Brief Introduction to the Scenery of the Imperial Capital" contained: "On the winter solstice, a plum blossom is painted, which is one in eighty petals. Dye one petal a day, and the petals will come out in 99, then the spring will be deep, saying that 99 will eliminate the cold. " In addition, there were "Poems and Pictures for Eliminating Cold in 1999" in Qing Dynasty.

There are four sentences and * * * thirty-six sentences in the picture every nine days, ranging from "san huang's rule of the world" in ancient times to "Qing Dynasty's golden jubilee" in this dynasty, which can be called an elegant historical "memorabilia".

after "painting nine", the custom of "writing nine" appeared in Qing dynasty. "Writing Nine" has a strong cultural flavor, and the characters "weeping willows in front of the pavilion cherish the spring breeze" or "sending fragrant flowers to the room in the spring vestibule" (traditional) are often used. First, they are hooked into a picture and filled in from the first day of the ninth (similar to "painting red" in calligraphy practice).

Use a thick brush to paint black, with nine strokes per word, one stroke per day, and it takes exactly 81 days to complete the nine strokes. Interestingly, after filling in a stroke every day, you have to use a fine brush to record the weather on the stroke that day. Therefore, a line of "writing nine" is also a more detailed meteorological data in the past nine days.

Baidu Encyclopedia-Counting Nine Cold Days