Solar term
A solar term (Chinese: 節氣; pinyin: jiéqì) is one of the 24 segments into which the traditional Chinese lunisolar calendar divides the solar year, each corresponding to a specific astronomical event where the Sun reaches successive multiples of 15° along its ecliptic longitude from the vernal equinox.[1] These terms, lasting approximately 15 days each, mark subtle transitions in seasons, climate, and natural phenomena, serving as a solar complement to the lunar months.[2] The system originated in the Yellow River region through ancient observations of the Sun's annual motion, with its formal structure established in 104 BCE during the Taichu calendar reform under Emperor Wu of the Han dynasty, which integrated the 24 terms into official use for timekeeping and agriculture.[3] Prior to this, earlier dynasties like the Zhou (c. 1046–256 BCE) recognized eight principal terms, but the full 24 were refined to align the calendar more precisely with solar cycles, incorporating both major (zhōngqì) and minor (jiéqì) divisions that interlace to guide intercalary months.[4] This astronomical framework, based on the geocentric apparent position of the Sun, has evolved from fixed even divisions (píngqì) to the modern dìngqì system adopted in 1645 CE, which accounts for the Sun's variable orbital speed.[2] Beyond their calendrical role, solar terms hold profound cultural significance in China, informing farming practices, dietary customs, festivals, and daily life across diverse ethnic groups, as recognized by UNESCO's inscription in 2016 on the Representative List of the Intangible Cultural Heritage of Humanity.[5] For instance, terms like Lìchūn (Start of Spring) signal planting seasons, while others inspire rituals, proverbs, and traditional medicine, fostering intergenerational transmission of environmental knowledge.[5] Today, they remain integrated into contemporary Chinese society, appearing in almanacs, weather forecasts, and even the Gregorian calendar dates, underscoring their enduring relevance in harmonizing human activities with natural rhythms.[1]Definition and History
Definition
Solar terms, known as jiéqì (節氣) in Chinese, are 24 specific periods that divide the traditional Chinese lunisolar calendar, each aligned with key astronomical events or observable natural phenomena such as seasonal transitions in weather, agriculture, and wildlife. These terms originated from ancient observations in the Yellow River basin, where they served as markers for climatic changes and guided daily life, particularly farming activities.[5][1] The solar year is partitioned into these 24 equal segments, each spanning approximately 15 days or 15 degrees of the sun's apparent motion along the ecliptic, beginning conventionally from the winter solstice. This division provides a solar framework that ensures the calendar remains synchronized with the Earth's orbit around the sun, reflecting the annual cycle of seasons.[6][7] Among the 24 terms, a distinction exists between the 12 principal terms, or zhōngqì (中氣), which occur at even-numbered positions (multiples of 30 degrees) and include the four major astronomical points—the winter solstice, spring equinox, summer solstice, and autumn equinox—and the 12 subsidiary terms, or jiéqì (節氣), at odd-numbered positions (15 degrees offset). The zhōngqì historically played a central role in defining the progression of solar months, while the jiéqì marked intermediate seasonal shifts.[6][8] By integrating these solar divisions with the lunar phases, the system forms a comprehensive lunisolar calendar that balances monthly lunar cycles with annual solar progression, enabling accurate timing for traditional festivals, agricultural planting and harvesting, and cultural practices across Chinese communities.[5][9]Historical Development
The solar terms system originated in the middle and lower reaches of the Yellow River basin around the 5th century BCE, where ancient farmers developed it as a practical tool for timing agricultural activities based on observations of seasonal changes and solar positions.[5][10] This early framework reflected the agrarian needs of communities in the region, marking key transitions in weather, crop growth, and phenological events to guide planting, harvesting, and other farming practices.[1] During the Spring and Autumn Period (770–476 BCE) and the subsequent Warring States Period (475–221 BCE), the system evolved from simpler divisions, such as the initial four seasonal terms, into an eight-term structure that provided more granular seasonal indicators, including terms like Mid-Spring, Mid-Summer, Mid-Autumn, and Mid-Winter.[10] By the late Warring States era, this progressed toward the standardized twenty-four solar terms, incorporating finer astronomical and climatic distinctions to better align with agricultural cycles and natural phenomena observed in the Yellow River valley.[10] The system was formalized during the Han Dynasty (206 BCE–220 CE), particularly with its inclusion in the Taichu Calendar promulgated in 104 BCE under Emperor Wu, where astronomer Deng Ping systematically classified the twenty-four terms according to their solar longitudes.[10] This calendar reform marked a significant milestone, embedding the solar terms into official Chinese calendrical practice and ensuring their widespread adoption for both agricultural and ritual purposes across the empire.[1] In recognition of its enduring value as a knowledge system derived from solar observations, the twenty-four solar terms were inscribed on UNESCO's Representative List of the Intangible Cultural Heritage of Humanity in 2016, highlighting its origins in ancient Chinese practices and its ongoing relevance in understanding seasonal time.[5]Astronomical Basis
Determination and Calculation
Solar terms are defined astronomically by the apparent geocentric ecliptic longitude of the Sun, which advances at varying rates due to Earth's orbital motion. Each of the twenty-four terms occurs when this longitude reaches successive multiples of 15°, effectively dividing the ecliptic's 360° circuit into equal 15° segments. This positioning ensures that the terms align with key points in the Sun's annual path relative to Earth, independent of lunar phases or calendar months.[2][1] A common approximate formula for estimating the date of the nth solar term—where n ranges from 0 to 23, starting with Dongzhi (winter solstice) as n=0—adds (n × 365.2422 / 24) days to the winter solstice, using the tropical year's length of 365.2422 mean solar days to distribute the terms evenly. Lichun corresponds to n=3 in this scheme. This yields intervals of about 15.22 days between terms, but actual timings vary slightly and require corrections for leap years in the Gregorian calendar to synchronize with civil dates, as well as adjustments for precession of the equinoxes to preserve seasonal relevance over centuries. For precision, the formula assumes a starting point at the winter solstice (corresponding to 270° longitude), with subsequent terms following the angular progression.[2] Historically, ancient Chinese astronomers calculated solar terms through direct observations using gnomons—vertical poles placed in level ground—measuring the length and direction of shadows at solar noon on clear days. These shadow lengths, recorded for each term, allowed inference of the Sun's declination and ecliptic position, as documented in classical texts like the Zhoubi Suanjing, which tabulated gnomon shadows for the twenty-four terms to calibrate calendars and predict seasonal changes. Such methods relied on empirical data accumulated over generations, achieving accuracies sufficient for agricultural planning despite limitations from atmospheric conditions and instrumental precision.[11][12] In modern practice, solar term timings are determined using high-precision ephemerides that model Earth's orbit with full accounting for its eccentricity (approximately 0.0167), axial tilt, and gravitational perturbations from other bodies. Algorithms based on systems like NASA's Jet Propulsion Laboratory (JPL) Horizons compute the exact instants when the Sun's apparent ecliptic longitude hits the required multiples of 15°, often to within seconds. These computations distinguish apparent solar time—reflecting the Sun's true, irregular motion as seen from Earth—from mean solar time, which assumes uniform 24-hour days; the difference, known as the equation of time, can reach up to 16 minutes and arises primarily from orbital eccentricity and obliquity, ensuring the terms capture real astronomical events rather than averaged ones.[13][14]Numbering Systems
In traditional Chinese calendrical systems, the twenty-four solar terms are numbered sequentially starting with Lichun (Start of Spring) as the first term, marking the beginning of the annual cycle around the vernal equinox and proceeding in a counterclockwise direction along the ecliptic. This ordering aligns the terms with the progression of seasons, emphasizing agricultural and phenological cycles from spring onward.[15][9] An alternative numbering scheme, used in certain astronomical and calendrical contexts, begins with Dongzhi (Winter Solstice) as the first term, treating it as the pivotal point of the solar year due to its alignment with the ecliptic longitude of 270 degrees. In this system, odd-numbered terms are designated as major solar terms (zhōngqì), associated with key seasonal transitions, while even-numbered ones are minor (jiéqì), focusing on intermediate climatic shifts. This approach facilitates precise solar positioning calculations and is referenced in traditional almanacs for determining intercalary months.[16][2] The solar terms also correspond to the twelve zodiac signs of the traditional Chinese system, known as the earthly branches, with two terms allocated to each sign to reflect the sun's passage through 30-degree segments of the ecliptic. For instance, Lìchūn (Start of Spring) and Yǔshuǐ (Rain Water) fall within the Yín (Tiger) earthly branch period, guiding seasonal activities tied to that branch's attributes. This dual structure integrates the terms into the broader sexagenary cycle, linking astronomical events to zodiacal symbolism.[15][17] In modern international contexts, the solar terms have been adapted to align with fixed approximate dates on the Gregorian calendar, enabling global reference without reliance on traditional lunisolar computations. This synchronization, promoted through UNESCO recognition, supports cross-cultural applications in agriculture, meteorology, and cultural festivals, while preserving the terms' original 15-degree ecliptic intervals.[5][18]The Twenty-Four Solar Terms
List in English
The twenty-four solar terms are traditionally ordered starting from the Start of Spring and grouped into four seasons of six terms each: spring (terms 1–6), summer (terms 7–12), autumn (terms 13–18), and winter (terms 19–24).[2][19] The 24 terms comprise 12 jieqi (節氣, the terms that begin each of the 12 solar months) and 12 zhongqi (中氣, the mid-month principal terms); in this traditional ordering starting from Lichun, the odd-numbered terms are jieqi and the even-numbered are zhongqi.[9] Each term corresponds to a specific solar longitude, occurring when the Sun reaches multiples of 15° ecliptic longitude, with approximate Gregorian calendar dates that vary by 1–2 days annually due to the Earth's orbit.[19] The following table enumerates them with brief descriptions of associated seasonal or natural phenomena.[9][2]| No. | Type | English Name | Solar Longitude | Approximate Date | Description |
|---|---|---|---|---|---|
| 1 | Jieqi | Start of Spring | 315° | February 4 | Marks the beginning of spring, with warmer temperatures and the revival of yang energy.[9] |
| 2 | Zhongqi | Rain Water | 330° | February 19 | Increased rainfall moistens the soil, promoting early plant growth.[9] |
| 3 | Jieqi | Waking of Insects | 345° | March 6 | Hibernating insects and animals awaken as thunder signals the end of winter.[9] |
| 4 | Zhongqi | Spring Equinox | 0° | March 21 | Day and night are of equal length, with balanced yin and yang.[9] |
| 5 | Jieqi | Pure Brightness | 15° | April 5 | Weather becomes warm and bright, ideal for outdoor activities.[9] |
| 6 | Zhongqi | Grain Rain | 30° | April 20 | Abundant rain nourishes the growth of grains and crops.[9] |
| 7 | Jieqi | Start of Summer | 45° | May 6 | Summer commences with rising temperatures and longer days.[9] |
| 8 | Zhongqi | Lesser Fullness | 60° | May 21 | Grains and crops begin to fill out, indicating fullness in growth.[9] |
| 9 | Jieqi | Grain in Beard | 75° | June 6 | Wheat and other grains develop beards, signaling ripening.[9] |
| 10 | Zhongqi | Summer Solstice | 90° | June 22 | The longest day and shortest night of the year occurs.[9] |
| 11 | Jieqi | Lesser Heat | 105° | July 7 | The first period of intense summer heat begins.[9] |
| 12 | Zhongqi | Greater Heat | 120° | July 23 | The hottest period of the year, with peak summer temperatures.[9] |
| 13 | Jieqi | Start of Autumn | 135° | August 8 | Autumn begins as yang energy wanes and yin rises.[9] |
| 14 | Zhongqi | End of Heat | 150° | August 23 | The heat of summer gradually subsides.[9] |
| 15 | Jieqi | White Dew | 165° | September 8 | Cool dew condenses at night, turning white on plants.[9] |
| 16 | Zhongqi | Autumn Equinox | 180° | September 23 | Day and night are equal again, marking mid-autumn.[9] |
| 17 | Jieqi | Cold Dew | 195° | October 8 | Dew becomes colder, heralding the approach of frost.[9] |
| 18 | Zhongqi | Frost's Descent | 210° | October 23 | Frost begins to form in many regions.[9] |
| 19 | Jieqi | Start of Winter | 225° | November 7 | Winter arrives with colder winds and declining temperatures.[9] |
| 20 | Zhongqi | Lesser Snow | 240° | November 22 | Snow may begin to fall in northern areas.[9] |
| 21 | Jieqi | Greater Snow | 255° | December 7 | Heavier snowfall occurs, covering the landscape.[9] |
| 22 | Zhongqi | Winter Solstice | 270° | December 22 | The shortest day and longest night of the year.[9] |
| 23 | Jieqi | Lesser Cold | 285° | January 6 | A period of relatively cold weather before the peak of winter.[9] |
| 24 | Zhongqi | Greater Cold | 300° | January 20 | The coldest time of the year, with severe low temperatures.[9] |
Multilingual Names
The 24 solar terms, originating from the traditional Chinese calendar, have been adopted and adapted in other East Asian cultures, retaining the original Chinese characters (hanzi/kanji/hanja) while developing distinct pronunciations and romanizations in each language. These names reflect linguistic equivalences rooted in shared Sino-Xenic vocabulary, with minor variations in spelling or usage due to phonological differences. Below is a comprehensive catalog of the terms in Chinese (with pinyin), Japanese (with romaji), Korean (with Revised Romanization), and Vietnamese (using its romanized script, Hán Việt).[15][20][21][22]| # | Chinese (Characters / Pinyin) | Japanese (Kanji / Romaji) | Korean (Hanja / Hangul / Romanization) | Vietnamese (Romanized) |
|---|---|---|---|---|
| 1 | 立春 / Lìchūn | 立春 / Risshun | 立春 / 입춘 / Ipchun | Lập Xuân |
| 2 | 雨水 / Yǔshuǐ | 雨水 / Usui | 雨水 / 우수 / Usu | Vũ Thủy |
| 3 | 惊蛰 / Jīngzhé | 驚蟄 / Keichitsu | 驚蟄 / 경칩 / Gyeongchip | Kinh Trập |
| 4 | 春分 / Chūnfēn | 春分 / Shunbun | 春分 / 춘분 / Chunbun | Xuân Phân |
| 5 | 清明 / Qīngmíng | 清明 / Seimei | 清明 / 청명 / Cheongmyeong | Thanh Minh |
| 6 | 谷雨 / Gǔyǔ | 穀雨 / Kokuu | 穀雨 / 곡우 / Goku | Cốc Vũ |
| 7 | 立夏 / Lìxià | 立夏 / Rikka | 立夏 / 입하 / Ipha | Lập Hạ |
| 8 | 小满 / Xiǎomǎn | 小満 / Shōman | 小滿 / 소만 / Soman | Tiểu Mãn |
| 9 | 芒种 / Mángzhòng | 芒種 / Bōshu | 芒種 / 망종 / Mangjong | Mang Chủng |
| 10 | 夏至 / Xiàzhì | 夏至 / Geshi | 夏至 / 하지 / Haji | Hạ Chí |
| 11 | 小暑 / Xiǎoshǔ | 小暑 / Shōsho | 小暑 / 소서 / Soseo | Tiểu Thử |
| 12 | 大暑 / Dàshǔ | 大暑 / Taisho | 大暑 / 대서 / Daeseo | Đại Thử |
| 13 | 立秋 / Lìqiū | 立秋 / Risshū | 立秋 / 입추 / Ipchu | Lập Thu |
| 14 | 处暑 / Chùshǔ | 処暑 / Shosho | 處暑 / 처서 / Cheoseo | Xử Thử |
| 15 | 白露 / Báilù | 白露 / Hakuro | 白露 / 백로 / Baekro | Bạch Lộ |
| 16 | 秋分 / Qiūfēn | 秋分 / Shūbun | 秋分 / 추분 / Chubun | Thu Phân |
| 17 | 寒露 / Hánlù | 寒露 / Kanro | 寒露 / 한로 / Hanro | Hàn Lộ |
| 18 | 霜降 / Shuāngjiàng | 霜降 / Sōkō | 霜降 / 상강 / Sanggang | Sương Giáng |
| 19 | 立冬 / Lìdōng | 立冬 / Rittō | 立冬 / 입동 / Ipdong | Lập Đông |
| 20 | 小雪 / Xiǎoxuě | 小雪 / Shōsetsu | 小雪 / 소설 / Soseol | Tiểu Tuyết |
| 21 | 大雪 / Dàxuě | 大雪 / Daisetsu | 大雪 / 대설 / Daeseol | Đại Tuyết |
| 22 | 冬至 / Dōngzhì | 冬至 / Tōji | 冬至 / 동지 / Dongji | Đông Chí |
| 23 | 小寒 / Xiǎohán | 小寒 / Shōkan | 小寒 / 소한 / Sohan | Tiểu Hàn |
| 24 | 大寒 / Dàhán | 大寒 / Dakan | 大寒 / 대한 / daehan | Đại Hàn |
Chinese Mnemonic Song
The Chinese mnemonic song for the 24 solar terms, known as the Jiéqì Gē (节气歌), is a concise rhyme that encodes the sequence of terms for easy recall through poetic rhythm and seasonal grouping.[23] This traditional verse divides the terms into four seasonal clusters—spring, summer, autumn, and winter—each comprising six terms, facilitating memorization by associating them with natural phenomena and phonetic patterns.[23] The full text of the song in Chinese characters is:春雨惊春清谷天，In pinyin romanization, it reads:
夏满芒夏暑相连，
秋处露秋寒霜降，
冬雪雪冬小大寒。
Chūn yǔ jīng chūn qīng gǔ tiān,Each line uses seven characters to represent the six solar terms of a season (with the first two characters indicating the season), relying on rhyme (e.g., "tiān" with "lián," "jiàng" with "hán") and alliteration for auditory retention.[23] This traditional mnemonic song has served as an oral tool for education and agriculture, enabling farmers and scholars to transmit seasonal knowledge across generations without written aids.[24] Its enduring simplicity has made it a cornerstone of cultural memory, still recited today to link the Chinese terms—such as Lìchūn (立春) for Start of Spring and Dàxuě (大雪) for Major Snow—with practical seasonal timing.[24]
Xià mǎn máng xià shǔ xiāng lián,
Qiū chù lù qiū hán shuāng jiàng,
Dōng xuě xuě dōng xiǎo dà hán.