What is the origin of the solar term song?

Twenty-four solar terms originated in the Yellow River Basin.

As early as the Spring and Autumn Period, four solar terms have been set, namely, mid-spring, mid-summer, mid-autumn and mid-winter. After continuous improvement and perfection, by the Qin and Han Dynasties, the 24 solar terms had been completely established.

In BC 104, the taichu calendar written by Deng Ping officially set 24 solar terms in the calendar, and defined the astronomical position of the 24 solar terms.

The earth rotates once a day and revolves around the sun once a year. 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 has 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 rounded corner of the earth's orbit around the sun is 360 degrees. According to the climate change of direct sunlight in different parts of the earth, our ancestors divided a solar term every 15 degrees, and each solar term was about 15 days apart. In this way, there are two solar terms every month, twelve months a year, which just synthesize twenty-four solar terms.

Among them, the first solar term of each month is "solar term", namely: beginning of spring, Jing Zhe, Qingming, Changxia, Mangzhong, Xiaoshu, beginning of autumn, Bailu, Hanlu, beginning of winter, heavy snow and slight cold; The second solar term of each month is "Zhongqi", that is, the twelve solar terms: rain, vernal equinox, Grain Rain, Xiaoman, summer solstice, great summer heat, early Shu, autumn equinox, first frost, light snow, winter solstice and great cold.

"Solar terms" and "neutral qi" appear alternately, each lasting fifteen days. Now people have collectively referred to them as "solar terms". Solar terms refer to the climate change, and the 24 solar terms refer to the average division into 24 stages according to the climate change in one year.

Among them, beginning of spring, vernal equinox, long summer, summer solstice, beginning of autumn, autumnal equinox, beginning of winter and winter solstice are used to divide the four seasons of a year; "Dichotomy" and "Erzhi" are turning points of the season.

"Li Si" means the beginning of the season; Slight heat, great heat, intense heat, slight cold and severe cold represent the hottest and coldest periods of the year; White dew, cold dew and first frost reflect the process and degree of cooling.

Rain, Grain Rain, light snow and heavy snow reflect the degree of rainfall and snowfall; Stunning, clear, small full and awn grass reflect the season and the growth of crops.

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 rain shocks spring and clear valley days, summer is full and summer is even, autumn mildew and autumn frost, and winter snow is snowy.