How did the ancients master solar terms and chronology?

1. The ancients discovered the correlation between the change of celestial shadow length caused by the change of solar height and the change of annual cycle, and then established the earliest solar terms-summer solstice, winter solstice, vernal equinox and autumn equinox. The time interval between two winter solstice days or summer solstice days is a tropical year. After determining the cycle of the tropic year, people divide a year into 24 equal parts, that is, they get 24 solar terms.

2. The twenty-four solar terms are the crystallization of the experience and wisdom of the ancient working people in China, which is of great significance for guiding the ancient working people to master the farming season and rationally arrange farming activities. According to historical records, China has summed up the complete 24 solar terms in the Qin and Han Dynasties, and two or two solar terms in the 24 solar terms were recorded in the earlier Warring States Period.