The 24 solar terms is the complete name of the system that comprises of 12 major solar terms and 12 minor solar terms which are interlaced through the calendar. It depicts the changes in climate, guides agricultural practices and has had a huge affect upon the lives of Chinese people throughout the ages.

During the Spring and Autumn Period and Warring States Period, people began to use solar terms as a useful additional calendar. It was decreed that the 4 Solar Terms would accord to the 4 days which fall at exactly the middle of each of the seasons- mid-spring, mid-summer, mid-fall and mid-winter. By 104BC the 24 solar terms had finally been decided upon. In that year, the 24 solar terms were arranged into the Taichu Calendar by Deng Pin and several other astronomers of the Western Han region . The titles of the terms should not be taken as specific predictions of the exact weather of that solar term. For example, Heavy Snow does not necessarily mean it will snow heavily on that exact solar term, it is just a general reference.

China has a fantastic and long running agricultural history and a clear understanding of the laws of nature is essential to agricultural production. In ancient times, agricultural workers conducted their agricultural activities in accordance with the movements of the sun. The 24 solar terms takes into account the position of the sun and how it travels on an elliptical path returning to its original position year after year. In recognition of this we use the phrase ‘tropical year’. Each time it travels 15 degrees along the elliptical longitude, the solar period changes and this is why we have 24 solar terms.

The 24 Solar Terms originated from the region around the Yellow River. Therefore they accurately account for the weather and climate of this region. However they may not accord with the climate in other places around the world.