How are the 24 solar terms determined?

The vernal equinox and the autumnal equinox indicate that day and night are equal in length. "Divide" is equal share. These two solar terms are generally around March 20 and September 23 of the Gregorian calendar every year.

The solstice in summer and the solstice in winter mean that summer and winter have arrived. "To" means to arrive. Summer solstice and winter solstice are generally on June 2 1 day and February 22 12 of the Gregorian calendar every year.

The current 24 solar terms are derived from the "fixed gas method", which is divided into 24 specific solar terms according to the law of celestial movement to determine the starting point and end point of the four-season cycle. It is a knowledge system and social practice formed by the ancients by observing the movement of the sun for a year and understanding the changing laws of the four seasons, climate and phenology in a year.

It divides the trajectory of the sun in one year into 24 equal parts, and each equal part is a "solar term", collectively called "twenty-four solar terms".