Of the 24 solar terms in the Chinese lunar calendar, the winter solstice is the shortest day.

As an astronomical solar term, the winter solstice is also called "the night is long" and "the day is short". On the day of the winter solstice, the sun moves to 27 degrees of the Yellow Meridian (the winter solstice point), and the position where the sun points directly at the ground reaches the southernmost point of the year. The sun almost points directly at the tropic of Capricorn (also known as the winter solstice line), and the sun is most inclined to the northern hemisphere (China belongs to the northern hemisphere). Therefore, the winter solstice is the shortest day in a year in all parts of the northern hemisphere, and the farther north it is, the shorter the day is.

The winter solstice is an important solar term in the twenty-four solar terms of the Chinese lunar calendar, which usually falls on one of the days of December 21st, 22nd or 23rd of the Gregorian calendar every year. Astronomy regards the winter solstice as the beginning of winter, which is the first day of nine, but it is not the coldest time. This is because there is atmosphere and water on the earth's surface, which can store heat, not "save or lose" but "accumulate heat". After the winter solstice, although the solar altitude angle gradually increased, it was a slow recovery process, and the heat lost every day was 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. At this time, if there is the influence of Siberian cold air, the weather is even colder. After this "cold front", the weather will gradually get warmer. Therefore, it is said that it is "cold in March 9", and "September 9" is already in the first month and February of the second year of the lunar calendar, and most parts of China have entered the spring, so there is a saying of "sunny days in September 9".

the winter solstice is also a traditional festival of the Chinese nation, commonly known as the number nine, the winter festival, the winter festival, the sub-year-old festival, and the long festival. In ancient times, there was a saying that the winter solstice was as big as a year. According to records, in the Zhou and Qin Dynasties, winter and November were the first month, and the winter solstice was the first year to celebrate the New Year. However, the simple "Winter Solstice Festival" only appeared after the Han Dynasty, flourished in the Tang and Song Dynasties, and has been in existence ever since. Official routine holidays, officialdom popular mutual congratulations "winter worship" customs; When business trips are closed, relatives and friends give each other delicious food, visit each other and have a "quiet life" festival happily.

The traditional diet of the winter solstice is that jiaozi is eaten in the north and Tangyuan is eaten in the south, but apart from jiaozi and Tangyuan, the food of the winter solstice is different in thousands of miles. For example, killing chickens and pigs to eat "winter solstice meat" in Hunan. There is a proverb: "Eat the meat of the winter solstice, and the body is better than the calf." There is a custom of "offering to the winter solstice group" in Jiangnan area. The Winter Solstice Ball is made of glutinous rice flour and steamed with meat, vegetables, sugar, fruit, cowpea, red bean paste, shredded radish, etc. It is mainly used as a offering, and can also be used for entertaining guests or giving to relatives and neighbors. There is also a winter solstice custom of "wonton worshiping winter" in the northern region. Because "the shape of wonton is like a chicken egg, quite like the chaos of heaven and earth, so it is eaten on the winter solstice." In addition, Nanjing people eat shallots and tofu on the winter solstice, Changzhou people eat hot tofu overnight on the winter solstice, Guizhou people usually eat dog meat on the winter solstice, and Hangzhou people cook red bean rice and steam new rice cakes on the winter solstice, and so on.