In the Spring and Autumn Period, four solar terms, namely, midsummer, midsummer, midsummer and midwinter, were set. After continuous improvement and perfection, by the Qin and Han Dynasties, the 24 solar terms had been completely established. In 14 BC, taichu calendar, written by Deng Ping, officially set the twenty-four solar terms in the calendar, and defined the astronomical position of the twenty-four solar terms.
the time that the sun travels every 15 degrees along the yellow meridian from zero degree is called a solar term. It runs 36 degrees every year, and * * * experiences 24 solar terms, 2 times a month. Among them, the first solar term of each month is "solar term", namely: 12 solar terms such as beginning of spring, Jing Zhe, Qingming, long summer, Mangzhong, Xiaoshu, beginning of autumn, Bailu, Hanlu, beginning of winter, heavy snow and slight cold; The second solar term of each month is "Zhongqi", namely, 12 solar terms such as rain, vernal equinox, Grain Rain, Xiaoman, summer solstice, great summer heat, summer heat, autumn equinox, first frost, light snow, winter solstice and great cold. "Solar terms" and "neutral gas" appeared alternately, each lasting 15 days. Now people have collectively referred to "solar terms" and "neutral gas" as "solar terms".