Ancient Chinese identified the winter and summer solstices, and the spring and autumn equinoxes long time ago. In the Spring and Autumn Period and the Warring States Period, the number of the solar terms as documented in literature has been increased to eight: Beginning of Spring, Spring Equinox, Beginning of Summer, Summer Solstice, Beginning of Autumn, Autumn Equinox, Beginning of Winter, and Winter Solstice. These eight terms indicate the change of seasons, clearly marking the four seasons of the year.
During the Qin and Han Dynasties, the 24 solar terms were been fully established. Huai Nan Zi (Writings of the Masters South of the Huai River) of the Western Han Dynasty, for the first time in history, systematically, comprehensively and scientifically documented the division and observation and computation of the 24 solar terms, and recorded their names in full consistence with what they are called in modern times. This was the earliest record of the 24 solar terms in Chinese history.
In the seventh year of the Yuanfeng Period in the reign of Emperor Wu of the Han Dynasty (104 B.C.), Tai Chu Li (Genesis Calendar, or Grand Inception Calendar) as formulated by Deng Ping, Luoxia Hong and others, officially included the 24 solar terms in the calendar, and identified their astronomical locations.
The Twenty-four Solar Terms originated in the Yellow River reaches of China. The criteria for its formulation were developed through the observation of changes of astronomical time sequence, air temperature, precipitation, as well as other natural phenomena in this centred region. With a historically nationwide diffusion, it has been progressively applied as a time directory in the production and life of agricultural society and then shared by many ethnic groups.