Twenty-four solar terms and Huainanzi

Legend has it that the founder of solar terms is the Yellow Emperor, which may be inaccurate. However, in the Shang Dynasty in China, the lunar calendar was used. Because of the difference between the running time of the sun and the moon, it is necessary to set up a leap month, which must be based on solar terms, so solar terms have become an important feature of China calendar.

In Oracle Bone Inscriptions, there are already two words "Solstice" and "Sunrise", which mean summer Solstice and "Sunrise" is winter Solstice. In the Zhou Dynasty, it was clearly recorded in Shangshu: "The star bird in the sun is Yin Zhongchun; The sun is always shining for midsummer; In the night, the stars are empty and there is a cloudy Zhong Qiu; The sky is short and the stars are high, which is in the middle of winter. " Spring, summer, autumn and winter have been separated by solar terms. Yizhoushu has a complete sequence of 24 solar terms, but individual names are in different positions.

By the Warring States period, there were already 24 solar terms. But the name at that time was slightly different from today's. For example, the first rain in Lu's Spring and Autumn Annals is probably the later rain, and first frost is probably the later first frost. By the time Huainanzi was published, the names and order of the 24 solar terms were exactly the same as today, while Huainanzi was published in the Western Han Dynasty, which means that the 24 solar terms have been in China for more than two thousand years.

In BC 104, the taichu calendar written by Deng Ping officially set 24 solar terms in the calendar, and defined the astronomical position of the 24 solar terms. The ancients believed that the internal driving force of the operation of the 24 solar terms was the cycle of Yin and Yang, and Yin and Yang were in different positions in the world in different solar terms. As Guanzi Riding Horse said: "Spring, summer, autumn and winter, Yin and Yang are connected." Around the 24 solar terms, different folk activities have been formed in various places.