24 Solar Terms

Solar Terms is a calendar of twenty-four periods and climate to govern agricultural arrangements in ancient China and functions even now. As we have mentioned the Chinese calendar is a lunisolar calendar, it takes into account the longest and the shortest days and the two days each year when the length of the day equals that of the night. In other words, the significant days are the Summer Solstice, Winter Solstice and the Spring and Autumn Equinoxes.

Today the year comprises 24 Solar Terms. During the Shang Dynasty 商代 they only used four; the Zhou Dynasty 周朝 (11th century BC - 221BC), used eight; but it was in the Western Han 西漢 Dynasty (206BC - 24) that the 24 terms were finally decided upon.

These solar terms have meaningful titles. Some of them reflect the change of seasons such as the Beginning of Spring, the Beginning of Summer, the Beginning of Autumn, and the Beginning of Winter; some embody the phenomena of climate like the Waking of Insects (Jing Zhe 惊蛰), Pure Brightness (Qing Ming), Lesser Fullness of Grain (Xiao Man) and Grain in Beard (Mang Zhong 清明); and some indicate the change of climate like Rain Water (Yu Shui 雨水), Grain Rain (Gu Yu 谷雨), Lesser Heat (Xiao Shu 小暑), Greater Heat (Da Shu 大暑), and so on.

These twenty-four solar terms each suggest the position of the sun every time it travels 15 degrees on the ecliptic longitude. In each month there are often two solar terms; the first one is generally named 'Jie Qi' 節氣 and the other one 'Zhong Qi' 中氣. Their dates are mirrored by the Gregorian calendar, so we find that during the first half of a year 'Jie Qi' 節氣 is around the 4th-6th day of a solar month, 'Zhong Qi' 中氣 around the 19th-21st; in the second half of a year, 'Jie Qi' 節氣 is around the 7th-9th and 'Zhong Qi' 中氣 around the 22th-24th.