Mathematical content from winter to Japan and China

Winter solstice, also known as Winter Festival, New Year's Eve Festival and Long Day Festival, is regarded as a major winter festival with natural and humanistic connotations. It is not only an important solar term among the 24 solar terms, but also a traditional folk festival in China.

From winter to the sun, the sun reaches 270 degrees, and festivals are held every year on the Gregorian calendar 65438+February 2 1-23. It means that the height of the sun in the northern hemisphere is the smallest and the daytime is the shortest. But the winter solstice temperature is not the lowest. On the solstice of winter, the sun shines directly on the ground and reaches the southernmost tip of the year. The sun shines almost directly on the tropic of Capricorn (also known as the winter solstice daily line), and the sun is most biased towards the northern hemisphere. Therefore, in all parts of the northern hemisphere, the winter solstice is the shortest day in a year, and the farther north, the shorter the day.

"Jiujiu", also known as "Winter Jiujiu", is a folk solar term in winter in China. "Nine" is a unit every nine days from the day of the annual "Winter Solstice". The first nine days are called "September 19th", the last nine days are called "February 9th", and so on until "September 9th".