How is the Sun, the Earth and the Weather, this year’s World Meteorological Day theme, correlate with 24 Solar Terms? How does 24 Solar Terms originate from?

Reporter from China Meteorological News Press interviewed Mao Liuxi, senior engineer from National Meteorological Center (NMC) of China Meteorological Administration.

Reporter: How did people in ancient times judge the time and solar terms?

Mao Liuxi: people in ancient times judged the time and solar terms based on the Sun. The shadow forms when the Sun shine over things on earth serves as a pointer.

During long-term production and life practices, ancient people observed that the length of the day and night within the year and the height of the Sun at noon were constantly changing. Shadows of woods and houses after shone over by the Sun were regular on a year-on-year basis. Counting the time based on the location of shadows within the day and the change of the length of shadows within a year is counted as seasons. They will erect a rod on the ground and observe the length of the shadow of the rod at noon then they can finalize the rough season. This instrument was gnomon. Subsequently, they found that during one day in summer, the length of the shadow was the shortest, and the length was the longest during one day in winter. These two days were the subsequent Summer Solstice and Winter Solstice.

A gnomon, the lengths of the shadow during Summer Solstice and Winter Solstice Photoed by Yu Long Source: Chinese National Geography

To more accurately measure the length of the Sun’s shadow, ancient people placed one ruler on the ground, called earth sundial. After many years’ evolution, the gnomon was finally made in a bid to determine solar terms and the length of times in one year.

China’s 24 Solar Terms is a knowledge system and social practice formed through observations of the sun's annual motion, and cognition of the year's changes in season, climate and phenology.Ancient Chinese divided the Sun’s movement through the sky into 24 segments, with each segment equaling one roughly two-week-long “solar term”.The 24 Solar Terms each suggests the position of the sun every time it travels 15 degrees on the ecliptic longitude.

Smart “coordination” changing with weather and climate

Reporter: China has an immense land and the 24 solar terms originated from the Yellow River Basin cannot be applicable to the entire country. How do people from all places manage to tackle this problem?

Mao Liuxi: although 24 solar terms sprang from the Yellow River Basin near 35°N and guided agricultural activities in these places. But it can be applied by places from south to north in China. People from different places have made smart localized revisions combined with local weather and climate.

Yellow River Basin is a rare region in the world which has Greater Heat and Greater Cold at the same time. Under this climate, agriculture calls for guidance. Climate formation is mainly influenced by solar radiation, geographical position (longitude, latitude, and altitude), the distance from the ocean, earth movement, and atmospheric circulation. 24 Solar Terms objectively manifests climate features, raining and hot during the same period and four distinctive seasons in China. 24 Solar Terms points out the most dominant climate feature and rule (winter is cold and the summer is hot).

24 Solar Terms is like coordination. People from various localities will find appropriate agricultural activities nodes in the coordination coupled with local weather and climate features. Due to the disparities of climate in those regions, axioms passed down about solar terms are different as well.

24 Solar Terms, when combined with local weather and climate has exuded diverse glamor, which is more dynamic.

Reporter: will 24 solar terms go out of date?

Mao Liuxi: weather and climate change are common. And 24 Solar Terms will not go out of date because of weather and climate change. Actually, 24 Solar Terms does not remain unchanged and go through constant evolution and improvement. In terms of temporal and spatial spheres, new contents will be added, like new agricultural technologies, agricultural activities, and new solar terms axioms.

A more popular “global language”

Reporter: as China’s 24 Solar Terms was added to the United Nations Educational, Scientific and Cultural Organization’s (UNESCO) world intangible cultural heritage list, it has become an increasingly popular “global language”. how should we better pass down its cultural values?

Mao Liuxi:24 Solar Terms not only deeply impacts people’s way of thinking and behavioral habits, but also embodies the capacity of human being to live in harmony with nature. It has fully manifested the concept of respecting nature and complying with nature’s law, coincided with the pursuit of sustainable development in the contemporary world, and signified powerful realistic value and importance.

24 Solar Terms is adored by a mounting number of people for its inheritance, recognition and integration. And the corresponding diet, recreation, and other cultures are integrating into it. Perfect combination of changes with each passing day and inheritance of ancient culture is the spring for its glamour.

Reporter: Yan Xin

Editor: Liu Shuqiao