45 days apart, the winter solstice is followed by slight cold, severe cold and beginning of spring, and every 15 days is a solar term; The annual movement track of the sun is divided into 24 equal parts, each equal part is15, and each equal part is a solar term, starting from the beginning of spring, ending in severe cold, and repeating.

Each solar term represents the different changes of climate, phenology and time. The lunar calendar in China is a combination of yin and yang, which is based on the sun and the moon's movement, so adding 24 solar terms can better reflect the cycle of the sun's movement.

It is a knowledge system formed by observing the annual movement of the sun and recognizing the changing laws of seasons, climate and phenology in a year.

Extended data:

The solar terms reflecting the changes of the four seasons are: beginning of spring, Spring Equinox, long summer, Summer Solstice, beginning of autumn, Autumn Equinox, beginning of winter and Winter Solstice. Among them, beginning of spring, long summer, beginning of autumn and beginning of winter all called "four stands", which means the beginning of the four seasons.

There are five solar terms reflecting temperature changes: slight summer heat, great summer heat, summer heat, slight cold and great cold.

There are seven solar terms reflecting weather phenomena: rain, Grain Rain, Bailu, Cold Dew, first frost, light snow and heavy snow. There are four solar terms that reflect the phenological phenomenon: fright, Qingming, Xiaoman and Mangzhong.

References:

Baidu encyclopedia-solar terms