Why are the 24 solar terms so accurate?

24 solar terms is accurate because it is accurately divided according to the position of the sun on the ecliptic.

When the sun shines directly at the equator, it is designated as "the longitude of the Yellow River is zero", that is, the vernal equinox. From here, every advance of 15 degrees is a solar term, which extends downwards from the vernal equinox, Qingming, Grain Rain, Changxia and so on. After running for a week, it will return to the vernal equinox, which is a 360-degree tropic year, so it is divided into 24 solar terms.

"Twenty-four solar terms"

It is the product of ancient farming civilization, and it is a knowledge system formed by ancient ancestors by observing the movement of celestial bodies and understanding 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, and each 1 is a solar term, starting in beginning of spring and ending in severe cold.