How are the 24 solar terms decided?

As we all know, it takes a whole day for the earth to make a circle; It is a year for the earth to go around the sun. Solar terms are divided according to the orbit position of the earth around the sun and the angle formed by the oblique intersection of the earth's rotation axis (the connecting line between the north and south poles of the earth) and the orbit (the ecliptic plane). Twenty-four solar terms, that is to say, the earth is in twenty-four different positions in the orbit of revolution.

Because of the different positions of the earth in the orbit of revolution, the position where the sun shines on the earth is sometimes south, sometimes north and sometimes directly on the equator. In this way, the climate and the length of day and night have changed.

The circumference of the earth around the sun is 360 degrees. Our ancestors divided a solar term every fifteen degrees according to the climate change of direct sunlight in different parts of the earth, and each solar term was about fifteen days apart. In this way, there are two solar terms every month, twelve months a year, which just synthesize twenty-four solar terms. Therefore, solar terms mean changes in climatic conditions; Twenty-four solar terms mean that according to the climate change of a year, it is divided into twenty-four stages on average.

The order of the masterpieces of the twenty-four solar terms is: beginning of spring, Rain, Surprise, Equinox, Qingming, Grain Rain, Xiaoman, Mangzhong, Summer Solstice, Slight Summer, beginning of autumn, Early Summer, Millennium, Equinox, Cold Dew, Early Frost, beginning of winter, Light Snow, Heavy Snow, Winter Solstice, Slight Cold and Severe Cold.

In order to facilitate memory, the ancestors wrote a song "Twenty-four solar term song" in the order of the names of the solar terms above:

Spring rains shock spring and clear valleys, and midsummer is full of summer.

Autumn is as cold as ice, and winter is cold and cold.

In this solar term song, every word stands for a solar term except one or two words. For example, in the first sentence, "Spring rains begin with spring and bright valley days", except the word Tian, the other four words respectively represent six solar terms: (Li) spring, rain (water), earthquake (thorn), spring (minute), clear (bright) and valley (rain). Other sentences can be analogized.