Twenty-four Qi is a seasonal law summarized by ancient farmers in observing phenological changes, astronomical phenomena and planting work. Originally, it was based on the rotation of the Big Dipper. The ancients said, "bucket handle refers to the east, and the world is spring; Bucket handle's guide, it is summer all over the world now, and the "bucket handle" here refers to the "handle spoon" of the Big Dipper. The present 24 Qi is determined according to the position of the sun on the ecliptic.

Twenty-four Qi can be divided into twelve seasons and twelve middle Qi. The twelve solar terms are: beginning of spring, Jingzhe, Qingming, Changxia, Mangzhong, Xiaoshu, beginning of autumn, Bailu, Hanlu, beginning of winter, Heavy Snow and Slight Cold. The twelve kinds of qi are: rain, vernal equinox, Grain Rain, Xiaoman, summer solstice, great summer heat, summer heat, autumn equinox, first frost, light snow, winter solstice and severe cold. The twelve qi can correspond to different lunar months in turn, such as rain corresponding to the first month, vernal equinox corresponding to February, and so on, and summer corresponding to the sixth month of the lunar calendar. Exceptions will only occur in rare cases. Twenty-four solar terms have been used to this day.