The twenty-four solar terms are based on the solar calendar.

Twenty-four solar terms, we can think that the current solar calendar is divided. The twenty-four solar terms reflect the annual apparent motion of the sun, so their dates are relatively fixed in the Gregorian calendar. The solar terms in the first half of the year are on the 6th, the solar terms in the second half of the year are on the 8th and the solar terms are on the 23rd, with a difference of less than 1 ~ 2 days. But strictly speaking, the lunar calendar in China is actually a combination of yin and yang, which is based on the movement of the sun and the moon, so adding 24 solar terms can better reflect the cycle of the sun's movement.