The method of setting the 24 solar terms is to divide the length of a solar year into 24 equal parts, which are evenly distributed in one year. This method is called the method of balancing gas, which has been used until 1644 in traditional calendars. Of course, the Northern Song Dynasty also used the method of balancing qi.
In the traditional lunar calendar, the solar terms set by the sun movement and the months set by the moon movement are not fixed, and there are insurmountable contradictions. It often happens that the season has entered spring and the month is still in winter, that is, the season does not match the month. Adding a leap month is a last resort, and this contradiction cannot be eliminated. In order to solve this problem, Shen Kuo, a great scientist in the Northern Song Dynasty, made bold innovations and founded Qi Twelve Calendars.
12 calendar is a calendar system based entirely on solar terms. It is determined by 12 solar terms: beginning of spring 1, February 1, beginning of winter 1 ... 65438+ 1 in severe cold. Big moon 3 1, small moon 30. Generally, the big moon and the small moon appear alternately, but once in a normal year, three small moons are connected together. Although the moon's profit and loss has nothing to do with solar terms, it can be marked with "new moon" and "hope" in the calendar as the general content.
This is a pure solar calendar system, which is simple and convenient for all kinds of production activities. But it was impossible to be adopted in ancient times when the traditional forces were extremely powerful. In this regard, Shen Kuo has long predicted, saying: "This calendar theory, in particular, must be blamed, but when it is different, it will be useful to the speaker." As predicted by Shen Kuo, the course of history was attacked by some people until the Qing Dynasty. The "calendar" used by the Taiping Heavenly Kingdom and the Gregorian calendar used now are essentially similar to the twelve-year calendar. In 1930s, the principle of "Shore Calendar" used by the British Met Office to count agricultural climate was the same as that of 12 year calendar.