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Ancient Chinese societies divided the annual solar cycle into 24 time segments, known as “solar terms” (节气), by correlating the sun’s movement with seasonal changes. Passed down from generation to generation, the solar terms have played a significant role in shaping traditional farming practices, food choices, wellness routines, and social rituals for more than two millennia. China’s “24 Solar Terms” were designated as UNESCO Intangible Cultural Heritage in 2016.

Anchored by the Spring Equinox, Summer Solstice, Autumn Equinox, and Winter Solstice, the 24 solar terms correspond to positions at 15-degree intervals along the sun’s path on the ecliptic longitude, forming a complete 360-degree circle. Each term spans approximately 15 or 16 days. In everyday usage, a solar term generally refers to the specific day that marks the beginning of each period.

The earliest two solar terms—Solar South Maximum (日南至) and Solar North Maximum (日北至), equivalent to the Winter Solstice and Summer Solstice respectively—were established during the Spring and Autumn period (春秋时代, 8^th–5^th centuries BCE). By the end of the Warring States period (战国时代) in the 3^rd century BCE, eight solar terms—Start of Spring, Spring Equinox, Start of Summer, Summer Solstice, Start of Autumn, Autumn Equinox, Start of Winter, and Winter Solstice (立春, 春分, 立夏, 夏至, 立秋, 秋分, 立冬, 冬至)—had been established to mark the four seasons. The remaining solar terms were formalized during the Western Han dynasty (西汉, 3^rd century BCE–1^st century CE). Consequently, the definitions of most solar terms reflect the climate of the Western Han core territories, particularly the wheat-growing regions of the Central Plains (中原).

Farmers relied on the solar terms to anticipate seasonal patterns such as droughts or heavy rainfall, enabling them to adjust agricultural practices accordingly. In traditional farming, the solar terms functioned as a seasonal almanac, indicating optimal times for planting, harvesting, and other agricultural activities throughout the year. For example, spring storms were believed to awaken hibernating creatures, giving rise to the solar term Jingzhe (惊蛰, Awakening of Insects), the 15-day period before the Spring Equinox. This term marks increased insect activity and signals an important time for farmers to prepare fields for planting. Some solar terms are named after stages in the growth cycle of wheat, the major grain crop. Yushui (雨水, Rain Water), the 15-day period following the Start of Spring, indicates moderate rainfall and the beginning of planting. Guyu (谷雨, Grain Rain), the 15-day period before the Start of Summer, corresponds to rapid crop growth aided by abundant rain. Mangzhong (芒种, Grain in Ear), the 15-day period before the Summer Solstice, marks the time when grains begin to mature, while Dahan (大寒, Major Cold), the final solar term of the year, begins 30 days after the Winter Solstice and represents the coldest period climatologically.

Over the centuries, several solar terms have become embedded in Chinese customs. Qingming (清明, Clear and Bright), which falls 15 days after the Spring Equinox, is traditionally a time to honor ancestors and visit family tombs, and is commonly known as Tomb-Sweeping Day. Traditional Chinese medicine also associates each solar term with specific dietary and herbal recommendations based on climatic changes and bodily needs. For instance, during First Frost (降霜), the 15-day period before the beginning of winter, people are advised to consume foods that nourish the lungs and counteract dryness, such as turnips, pears, and lotus root. Other solar terms mark seasonal transitions, such as Chushu (处暑, End of Summer), which signals the shift from summer to autumn, and Daxue (大雪, Major Snow), which marks the transition from early winter to its coldest phase.

In modern times, the solar term system is no longer the primary guide for agricultural practice. Nevertheless, harmonized with the Gregorian calendar, it remains an important cultural reference in areas such as ancestor worship, wellness practices, dietary habits, and seasonal celebrations. Originating from long-term observations of the relationship between seasonal cycles and agricultural production, the system is rooted in variations in sunlight exposure and serves as a foundational framework for aligning human activities with natural rhythms. Despite technological advancement and urbanization, this enduring wisdom continues to influence farming, health, culture, and environmental awareness by emphasizing harmony between humans and nature.

Photo credit: Baidu.com