The twenty-four solar terms are delineated based on the position of the earth in its orbit around the sun and belong to the solar calendar. The earth's revolution around the sun is 360 degrees. The vernal equinox is 0 degrees, the Qingming Festival is 15 degrees, and every 15 degrees thereafter is a solar term. The dates are basically fixed in the solar calendar. The twenty-four solar terms are an original creation of the Chinese calendar and one of the glorious achievements of ancient Chinese science and culture.

The origin of the 24 solar terms

It is reported that as early as the Spring and Autumn Period and the Warring States Period, our country could already use Tugui (a pole erected on a flat surface) to measure the length of the shadow of the sun at noon. Determine the four solar terms of winter solstice, summer solstice, vernal equinox and autumnal equinox. In a year, the day with the shortest shadow of Tugui at noon is the summer solstice, the longest day is the winter solstice, and the day with moderate shadow length is the vernal or autumnal equinox. By the Qin and Han Dynasties, a complete concept of 24 solar terms had been formed.

In ancient times, a year was divided into 12 months, and each month had two solar terms. The first one is the solar term, and the last one is the middle Qi. Later generations collectively called the solar term and the middle Qi the solar term.

It can be seen from the naming of the 24 solar terms that the division of solar terms fully takes into account changes in natural phenomena such as seasons, climate, and phenology. Among them, the beginning of spring, the beginning of summer, the beginning of autumn, the beginning of winter, the vernal equinox, the autumnal equinox, the summer solstice and the winter solstice are used to reflect the seasons. The vernal equinox, autumnal equinox, summer solstice, and winter solstice are divided from an astronomical perspective and reflect the turning points of the sun's altitude changes. The beginning of spring, the beginning of summer, the beginning of autumn, and the beginning of winter reflect the beginning of the four seasons.

The five solar terms, namely Minor Heat, Major Heat, Chushu, Minor Cold and Major Cold, reflect changes in temperature. The four solar terms of rain, grain rain, light snow, and heavy snow reflect the precipitation phenomenon and indicate the time and intensity of rainfall and snowfall. The three solar terms of white dew, cold dew and frost ostensibly reflect the phenomenon of condensation and sublimation of water vapor, but in essence they reflect the process and degree of gradual decline in temperature: when the temperature drops to a certain level, water vapor condenses. The temperature continues to drop, not only does condensation increase, but it also gets cooler. When the temperature drops below zero degrees Celsius, water vapor condenses into frost.

Xiaoman and Mangzhong reflect the maturity and harvest of related crops; Jingzhe and Qingming reflect natural phenological phenomena, especially Jingzhe, which uses the first thunder in the sky and the resurgence of underground stinging insects to herald the coming of spring. return.