Why do we calculate the winter solstice according to the solar calendar? How did the ancients determine the winter solstice?

China used soil gauge to observe the length of the sun shadow to calculate solar terms. Obviously, on the summer solstice, the shadow of the pole is the shortest in a year; On the solstice in winter, the shadow of the pole is the longest in a year. This change in shadow length is easy to observe, so it is very accurate.

The ancients defined the winter solstice as a solar term, which was based on the running law of the sun's direct point on the earth, and had nothing to do with the moon. So I used the solar calendar.

The formulation of solar terms in China is similar to the Gregorian calendar, based on the sun. So, will appear. The winter solstice corresponds to the Gregorian calendar of 65438+February 2 1 to 23 every year. Because the winter solstice is not fixed on a certain day, it is called "live festival" like Qingming.

Extended data:

Climatic characteristics

The solstice of winter is about to enter the cold season, so people begin to count nine to calculate the cold days. Counting nine is a folk method to calculate the date of cold and hot summer in China. As the folk proverb says, "The solstice in summer is three years old, and the solstice in winter is nine years old. The number nine is counted from the winter solstice, every nine days is counted as a "nine", and so on.

Generally speaking, "March 9 and April 9" are the coldest times of the year. When you count to nine "nine days" (998 1 day), spring will be deep and warm, and everything will be full of vitality. It's time for spring ploughing. The number nine method is passed down from mouth to mouth among the people in our country, which has a history and lacks records. As for when it originated, there is no exact information.

The number nine is the experience summarized by the ancients on the basis of generations of production and life practice, using some ecological reflections and weather signs in nature. Due to the vast territory of China, the climate varies greatly from place to place. Only parts of China, not all parts of the country, correspond to the winter solstice "9981, 900 peach blossoms, deep spring and warm days".