When was the determination of the 24 solar terms?

During the Warring States period, in order to arrange agricultural production, people determined 24 solar terms a year, which was a great achievement in the calendar. During the Shang Dynasty, the calendar gradually became complete, and a year was divided into 12 months, 30 days for a big month, 29 days for a small month, and 1 month for a leap year.

The 24 solar terms are: beginning of spring, rain, fright, spring equinox, Qingming, Grain Rain, Changxia, Xiaoman, Mangzhong, Summer Solstice, Slight Summer, Great Summer, beginning of autumn, Summer Dew, Autumn Equinox, Cold Dew, First Frost, beginning of winter, Light Snow, Heavy Snow, Winter Solstice, Slight Cold and Great Summer.

"Twenty-four solar terms" is the product of ancient farming civilization. It is a knowledge system formed by ancient ancestors following the farming season and observing the movement of celestial bodies to understand the changing laws of seasons, climate and phenology in a year. The twenty-four solar terms were originally formulated according to the changes of stars. The Big Dipper rotates once and bucket handle rotates once clockwise, which is called one of the "years" (Figure). The current "twenty-four solar terms" are formulated according to the position of the sun on the return to the ecliptic, that is, the annual movement track of the sun is divided into 24 equal parts, each 15 is 1 equal part, and each 1 equal part is a solar term, starting from beginning of spring and ending from the severe cold.