How are the 24 solar terms of the lunar calendar divided?

The basis for the classification of the twenty-four solar terms:

The first category reflects the seasons.

Among them, beginning of spring, Changxia, beginning of autumn, beginning of winter, vernal equinox, autumnal equinox, summer solstice and winter solstice are used to reflect the seasons, and a year is divided into four seasons: spring, summer, autumn and winter. The vernal equinox, autumnal equinox, summer solstice and winter solstice are divided from an astronomical point of view, reflecting the turning point of solar height change. Beginning of spring, Changchun, beginning of autumn and beginning of winter reflect the beginning of the four seasons.

Because China has a vast territory, the monsoon and continental climate are very obvious, and the climate varies greatly from place to place, so the start date and duration of the four seasons are not the same. In some areas, the four seasons are distinct, in others, they are not obvious, or even do not appear for a whole season. For example, in the alpine region north of Aihui, there is no summer on the Qinghai-Tibet Plateau. On the Qinghai-Tibet Plateau, it is said that "it is still covered with cotton in the midsummer of June, and it is mostly cold all year round".

There is no winter in southern Fuzhou, South China, and it is summer in some areas almost all year round. It's really "the grass will not wither when winter goes and spring comes", "it's always summer, and when it rains, it becomes autumn"; Yunnan, Guizhou and other plateaus are another scene. Winter is short and there is no summer. Kunming is known as "four seasons like spring". Therefore, although "Li Si" is separated from astronomy, it has a strong regional character, and it is impossible for it to adapt to the whole country.

The second category reflects climate characteristics.

The five solar terms of slight summer heat, great summer heat, slight cold and severe cold reflect the change of temperature and are used to express the degree of heat and cold in different periods of the year; The four solar terms of rain, Grain Rain, light snow and heavy snow reflect the phenomenon of precipitation, indicating the time and intensity of rainfall and snowfall.

The three solar terms, White Dew, Cold Dew and First Frost, on the surface reflect the phenomenon of condensation and condensation of water vapor, but in essence reflect the process and degree of gradual temperature drop: when the temperature drops to a certain extent, water vapor condenses; The continuous drop in temperature not only increases condensation, but also gets colder and colder; When the temperature drops below zero degrees Celsius, water vapor condenses into frost. From the perspective of agricultural production, these three solar terms are concrete and vivid, with their heat meaning greater than their water meaning.

The third category reflects phenological phenomena. Xiaoman and awn species reflect the maturity and harvest of related crops; Frightening and Qingming reflect natural phenology, especially stinging. It uses the first thunder in the sky and the revival of underground stinging insects to inform everything in the world that spring is coming back to the earth.