When did the twenty-four solar terms begin to exist? Why are there 30 in Qi?

Twenty-four solar terms have been circulating in China for thousands of years. This is the wisdom handed down from the ancients. The ancients didn't know that the earth went around the sun. With the change of the sun's trajectory in the sky, there is a periodic change. The ancients initially divided this change into spring and autumn, and later added winter and summer.

Twenty-four solar terms originated in the Yellow River Basin. There are four solar terms in the Spring and Autumn Period, namely, mid-spring, mid-summer, mid-autumn and mid-winter. Later, after continuous improvement by later generations, the 24 solar terms were basically established in the Qin and Han dynasties, so there was the saying of four seasons, namely, spring, summer, autumn and winter, which has been passed down to this day.

In BC 104, the twenty-four solar terms were officially recorded in taichu calendar written by Deng Ping in the Western Han Dynasty, and the astronomical position of the twenty-four solar terms was clearly defined. The 30 solar terms of Qi are: the seven solar terms in winter are standing cold, slight cold, moderate cold, moderate cold, severe cold, the yin of severe cold and the end of severe cold. The seven stages of summer are Xiaoying, Exhausted, Ying Zhong, Moderately Exhausted, Mild Summer Arrival, Heatstroke and Late Summer. The eight stages of spring are, in turn, local atmosphere, small hair, weather, loyalty, Qingming, early hair, middle hair and down hair; The eight stages of autumn are wind arrival period, small base period, white dew period, restoration period, pre-festival, early base period, middle base period and lower base period in turn.

At that time, there were only ten months in a year, but every month was arranged in 36 days. At that time, the solar terms in other countries were different. Why do they use such a special method? It is said that the geographical position of Qi is quite special, because they have a long time in winter and summer. For the convenience of farming, they divided it into 30 solar terms.