“The twenty-four solar terms” is a unique phenomenon on the traditional lunar calendar. To facilitate agricultural production, ancient Chinese people summarized a supplementary calendar that divides a year into 24 segments according to the sun’s movement on the ecliptic and seasonal changes in weather and other natural phenomena, with the 24 solar terms proportionally distributed through the 12 months. A solar term that starts in the early part of a month is called jie (节), and one that starts in the middle part of a month is called qi (气). (Every three years there would be a month which has only a jie without a qi, or a month which has only a qi without a jie, in which case a leap month would be added to regulate it.) The solar terms are so named that they represent the changes in season, phenology and climate. The eight solar terms that reflect seasonal changes are Beginning of Spring, Vernal Equinox, Beginning of Summer, Summer Solstice, Beginning of Autumn, Autumnal Equinox, Beginning of Winter and Winter Solstice; the four solar terms that represent phenological changes are Waking of Insects, Fresh Green, Lesser Fullness and Grain in Ear; and the 12 solar terms that indicate the changes in climate are Rain Water, Grain Rain, Lesser Heat, Greater Heat, End of Heat, White Dew, Cold Dew, First Frost, Light Snow, Heavy Snow, Lesser Cold and Greater Cold. First established in the Qin and Han dynasties, the 24 solar periods have not only facilitated agricultural production but also reflected Chinese people’s perception of time in the past more than two thousand years.

Drizzles refresh all forms of greenery, and thunder startles hibernators awake. Farmers hardly have time to relax, and tilling the soil starts now.  (Wei Yingwu: Watching Farmers Working in Fields in Spring)