Why are the 24 solar terms called the lunar calendar?

The summer solstice and the winter solstice refer to the longest day and the longest night respectively, which are collectively called the extremes of the "second solstice" and "solstice".

The vernal equinox and autumnal equinox refer to two days as long as day and night respectively, which are collectively called "equal division" and stand for "equal division".

Beginning of spring, Chang Xia, beginning of autumn and beginning of winter are collectively called "four stands", and "stand" means "start".

The twenty-four solar terms are part of the lunar calendar, which is essentially a solar calendar. Now the common solar calendar is also a solar calendar, which naturally coincides with each other. The lunar calendar is a combination of yin and yang, and because of the composition of the lunar calendar, there is a big gap with the prevailing Gregorian calendar.

Twenty-four solar terms originated in the Yellow River basin and are based on the temperate monsoon climate characteristics in this latitude zone. However, China has a vast territory and diverse climate resources, so it is impossible to apply the 24 solar terms in vast areas outside the Central Plains, such as the temperate continental climate in Xinjiang and Inner Mongolia, the subtropical monsoon climate in Yunnan, Guangxi and the southeast coast, the plateau mountain climate in Tibet, and the tropical monsoon climate in Hainan, Yunnan and southwest Guangxi.