{
  "id": "twenty-four-solar-terms",
  "title": "Twenty-four Solar Terms",
  "lang": "en",
  "source_lang": "en",
  "summary": "A system of 24 seasonal divisions from traditional Chinese lunisolar calendars, tied to the sun's position and inscribed on UNESCO's heritage list in 2016.",
  "category": "society",
  "subcategory": "culture",
  "type": "concept",
  "aliases": [
    "二十四节气",
    "Jieqi",
    "Solar terms",
    "节气"
  ],
  "generated_at": "2026-10-15",
  "model": "pro/claude-haiku-5-5",
  "url": "https://aiwiki.page/en/twenty-four-solar-terms/",
  "translations": {
    "zh-Hans": {
      "url": "https://aiwiki.page/zh/twenty-four-solar-terms/",
      "json": "https://aiwiki.page/zh/twenty-four-solar-terms.json"
    }
  },
  "sections": [
    {
      "heading": "",
      "text": "The Twenty-four Solar Terms (二十四节气) are a time-keeping system from traditional China that divides the solar year into 24 named points, each tied to a particular astronomical position and a typical set of seasonal, climatic and biological conditions. Each point marks a 15° step of the sun's apparent path along the sun's ecliptic, so the terms divide the year by solar motion rather than by the phases of the Moon. Originating in the middle and lower reaches of the Yellow River, the system was incorporated into the state calendar in the Western Han period and has since served as a practical guide to farming, weather and daily life across the Chinese cultural sphere. It has also spread to neighbouring East Asian societies and is recognized as an intangible cultural heritage by UNESCO.\n\nThe entry explains the system as both an astronomical framework and a living cultural practice. It covers how the terms were defined and structured, how they developed historically from earlier seasonal divisions, and how they were combined with the Chinese lunisolar calendar. It then examines their use in agriculture, ritual and folk custom, their diffusion across East Asia, and their relevance to modern climate change research, where observed shifts in seasonal timing are compared with the traditional naming. The entry closes with the UNESCO inscription and the unresolved questions about origin, regional fit and modern validity."
    },
    {
      "heading": "Definition and astronomical basis",
      "text": "Solar longitude as the reference\n\nThe twenty-four solar terms (节气, jiéqì) are moments in the solar year that are fixed by the Sun's position rather than by the Moon. In modern astronomical terms, each term is defined as the time when the Sun's apparent geocentric ecliptic longitude reaches an integral multiple of 15°. The ecliptic is the Sun's apparent annual path against the stars, which is a great circle on the celestial sphere and represents Earth's orbital plane projected onto it. The count begins at the vernal equinox, where the Sun's longitude is 0 degree, and each following marker adds another 15°. Because a full circle is 360°, the markers form a closed cycle of twenty-four. Some sources number the terms from the winter solstice instead, and divide the ecliptic into 24 uniformly spaced sections from that point. This is a difference in enumeration, not in the underlying astronomical definition.\n\nUneven intervals in calendar days\n\nEqual angular steps do not produce equal time intervals. Earth's orbit is elliptical, so the apparent speed of the Sun along the ecliptic changes through the year. The number of days the Sun takes to travel between each pair of solar terms varies slightly through the year, but it is always between 15 and 16 days. In practice the Sun moves faster in the weeks around perihelion in early January and more slowly around aphelion in early July, so the spans between terms in the second half of the year tend to differ from those in the first half. This is why the terms are not uniform in length, even though each corresponds to exactly 15 degrees of longitude.\n\nPentads as a finer subdivision\n\nEach term is further divided into three pentads (候, hòu). Each solar term is divided into three pentads, so there are 72 pentads in a year, consisting of five, rarely six, days. The three pentads of a term are conventionally labelled first, second and last (初候, 次候, 末候). Because the pentads are derived from divisions of the tropical year, they are not fixed-length periods of exactly 120 hours; their lengths vary slightly like the terms themselves.\n\nContrast with lunar month reckoning\n\nThe solar terms measure the year by solar longitude, whereas the lunar calendar measures time by the phases of the Moon, with months of roughly 29.5 days. The two systems therefore run on different clocks. A term does not begin with a new moon or end with a full moon, and its date in the lunar calendar depends on where it falls relative to the lunar months. The terms are also not all of one kind. The system comprises 12 major solar terms and 12 minor solar terms interlaced with each other. The major terms fall at multiples of 30° and the minor terms at the intermediate odd multiples of 15°. This alternation is what allows the terms to be linked to the months of the lunisolar calendar, a relationship treated in a later section."
    },
    {
      "heading": "Origins and historical formation",
      "text": "Chinese accounts generally place the system's formation in the Yellow River basin, where observers based the terms on seasonal changes in celestial phenomena, temperature, precipitation, and phenology in that region. The chronology is built in stages, and the stages are dated differently across sources.\n\nThe earliest layer is usually described as a four-season framework. Records from the Spring and Autumn period (770–476 BC) are often read as marking two solar extremes, two major solar terms, ri nan zhi (日南至 'Sun South Most') and ri bei zhi (日北至 'Sun North Most'). By the end of the Warring States period, a set of eight markers covering the four seasons was in use, established according to the different positions of the sun and changes in natural phenomena. Some scholars push the origin further back. One study drawing on Shen (2001) treats the Shang dynasty as the earliest period with verifiable written records of calendar adjustment, noting that the Shang people used leap months to reconcile differences between the lunar and solar cycles. A Shang-period tomb at Xishuipo in Henan has also been read as aligned with the sun's equinox and winter solstice positions, though that reading is interpretive rather than settled.\n\nThe intermediate stage expanded the four markers. The Zuozhuan of the Spring and Autumn Period is cited for describing eight terms, including the \"Four Beginnings\" of spring, summer, autumn and winter. Other summaries place the move from four to eight in the Zhou period, during the Zhou dynasty (1046 BC to 256 BC), this was increased to eight, which is a date range that overlaps with the Spring and Autumn and Warring States sources above.\n\nThe step from eight to twenty-four is tied to the early Han. The earliest full list of names is usually traced to the book Huainanzi (around 139 BCE). The reform most often cited as formal adoption is the Taichu Calendar of 104 BC, not until the Taichu Calendar of 104 BC were all twenty-four solar terms officially included in the Chinese calendar. The astronomer Deng Ping is credited in some accounts with writing the terms into that calendar and classifying their astronomical positions. Other sources state that the rest of the solar terms were initiated in the Western Han Dynasty (206 BC–24 AD).\n\nThe chronology therefore remains contested. Accounts that begin the system in the Shang period rely on calendrical practice and tomb orientation rather than on explicit lists of named terms, while accounts that begin with the Han rely on the first full set of names and the 104 BC reform. Scholarly treatments note that exact origins of the system remain debated among the academic field. Readers should therefore treat the Shang and Zhou dates as the proposed starting points of an observational tradition, and the Han-era reform as the best-documented point of formal completion."
    },
    {
      "heading": "Names, sequence and seasonal grouping",
      "text": "The Chinese names of the 24 terms are short descriptive phrases, and most fall into two families. The first describes something a farmer could observe in the field or the wild. Jingzhe, usually rendered as the Awakening of Insects, refers to animals emerging after winter. Xiaoman, often translated as Grain Buds, describes grain that is swelling but has not yet ripened, and Mangzhong, rendered as Grain in Ear, marks the point when grain heads appear. The second family describes temperature or weather. Lichun, literally \"establishment of spring,\" opens the cycle, and Chushu is the 14th solar term and signifies the end of the hot summer season, which gives it the literal sense of a \"limit of heat.\"\n\nSequence and seasonal grouping\n\nThe cycle begins with Lichun at 315° of solar longitude, which falls in early February, and ends with Dahan, the final solar term of both winter and the entire year, which sits at 300° around 20 January. Because each term is anchored to a 15° arc of the ecliptic, the sequence can be read as a fixed loop. The four seasons each contain six terms: spring runs from Lichun through Guyu, summer from Lixia through Dashu, autumn from Liqiu through Shuangjiang, and winter from Lidong through Dahan. The sources give each term a date range of about two days rather than a single day, because the solar longitude fixes the moment of the term, and that moment falls on a different calendar day from year to year.\n\nThe paired characters 节 and 气\n\nEvery term carries two characters, and the terms alternate between them. The first character, 节 (jié), is commonly read as \"node\" or \"joint\"; the second, 气 (qì), means \"air\" or \"breath.\" One account explains that the term jieqi literally means \"nodes of energy\" and refers to the growing and declining energy of Yin and Yang through the year. In the traditional reckoning, each month contains one 节 point and one 中气 point, so Lichun (节) is followed by Yushui (气). The pairing therefore encodes both the boundary between seasonal phases and the qualities of climatic energy that accompany them.\n\nNaming variants across languages and sources\n\nThe English names are not standardised. Xiaoman appears as \"Grain Buds\" in one popular guide and as \"Lesser Full Grain\" in another, and Dahan is also rendered as \"Major Cold\" or \"Great Cold.\" The Chinese names are also read differently in neighbouring languages. Dahan appears as Dàhán, Daikan, Daehan, or Đại hàn in Chinese, Japanese, Korean and Vietnamese, respectively. Similarly, Chushu appears as Chǔshǔ, Shosho, Cheoseo, or Xử thử across the same languages. Lichun shows a parallel pattern, with Japanese and Korean readings that preserve the same characters in different phonetic forms. Where an English equivalent is given in this entry, it should be treated as a translation of convenience rather than an established name."
    },
    {
      "heading": "Relationship to the lunisolar and Gregorian calendars",
      "text": "A lunar month averages roughly 29.5 days, so twelve of them fall well short of a solar year. The lunisolar system must reconcile the tropical year with this shorter lunar year, and the solar terms supply the solar reference that keeps months tied to the seasons. By reconciling the time difference between the tropical year (approximately 365.24 days) and the Chinese calendar year (approximately 354.37 days), it ensures that the months correspond to the seasons. The mechanism is described in more detail in the Chinese calendar entry.\n\nThe placement of intercalary months follows directly from the spacing of the terms. Each lunar month contains one jieqi (節氣, a \"node\" term) and one zhongqi (中氣, a \"middle\" term), and the two together span about 30.5 days, which is longer than a lunation. The solar term and middle qi for each month would be delayed by 1 to 2 days compared to the previous month. Eventually, a month would arrive containing only a solar term but no middle qi, and this month was later designated as the intercalary month.\n\nThe rule itself was formalised in stages. Under the Taichu calendar of 104 BCE, a jieqi could fall in the second half of one month and the first half of the next, while a zhongqi had to fall within a single month. Should there, in any case, be a month without a zhongqi term, that month was then made an intercalary month of the preceding month. Later procedures changed the reference point. One account states that after the Tang Dynasty, the fixed intercalation cycle was abolished, and the intercalation method based on months without Zhongqi, using the Winter Solstice as the benchmark, was adopted. Over longer periods the cycle is commonly described as seven leap months in nineteen years: 19 tropical years contain 228 solar terms, while 235 Synodic month occur in the same period, resulting in 7 months without solar terms. Sources differ on the precise chronology of these refinements, so the details should be read as descriptions of the principle rather than a single fixed history.\n\nThe Gregorian calendar is also a solar calendar, and the two systems therefore rarely diverge by more than a day or two. As a result, the Gregorian dates of the 24 solar terms are almost the same every year, give or take one or two days. The underlying reason is that each term marks a precise instant, when the sun reaches a fixed ecliptic longitude, while a calendar date is a whole day in a fixed time zone. Chinese almanac computations are made for the 120°E meridian, which corresponds to UTC+8. The Gregorian average year of 365.2425 days is close to the 365.2422-day tropical year, so the Gregorian date of a given term drifts only slowly. In effect, the instant moves by roughly a quarter of a day against the clock each year, so the date usually lands on one of two adjacent days; the Gregorian leap-day insertion then pulls the date back by about one day at intervals of several years. The variation within the window is also affected by the sun's non-uniform speed along the ecliptic, which means the exact instant of each term cannot be read from a fixed table without calculation.\n\nBecause of this, the Gregorian dates are best treated as approximations. In the past, dates of 24 solar terms were published every year in the Chinese calendar. Modern reckoning rests on the actual motion of the sun rather than uniform spacing; in 1645, it was decided that the 24 solar terms were to be computed using the dínqì method, which takes into account the non-uniform motion of the Sun. The resulting dates are close to, but not identical with, the simple Gregorian dates given in popular tables."
    },
    {
      "heading": "Agricultural guidance and daily practice",
      "text": "In the agrarian economy of north China, the terms gave farming households a shared timetable. Farmers relied on them to determine the best times for planting, cultivating, and harvesting crops. Because the terms follow solar longitude rather than the moon, they offered a reference that did not drift against the seasons in the way a month-based date could. Regional needs also shaped the calendar: agricultural and other production demands pushed people to describe the terms according to the actual climate of each place.\n\nTask-linked terms\n\nSeveral names point directly to field work. Grain in Ear (芒种 Mángzhǒng) and Grain Full (小满 Xiǎomǎn) indicate specific agricultural practices. Early spring has a parallel pattern. Folk descriptions of Awakening of Insects (驚蛰 Jīngzhé) tie the term to spring thunder that begins to rumble, awakening hibernating animals. In the farming calendar, this period marked the start of spring fieldwork, including ploughing and early pest control, although the specific tasks varied by locality. Guides to Rain Water describe it as a good time for sowing.\n\nAutumn advice focused on protecting the harvest. Harvest timing was adjusted around the onset of dew and frost, so that crops could take advantage of rainfall and sunlight and be prepared for dew and frost. Around Start of Autumn, popular accounts stress sun-drying ripened grain before it spoils.\n\nHousehold routines\n\nSeveral terms were linked to domestic rhythms rather than to crops alone. For Rain Water, a common custom held that married daughters returned to their parents' homes to visit and express gratitude. Accounts from Sichuan describe the visit as including stewed pig's feet, chicken soup, and red tapes as presents. At the beginning of spring, households were advised to open windows more often to allow air to circulate around the house, a practice that, in the sources, is presented as part of seasonal housekeeping rather than as a technical measure.\n\nSeasonal dietary customs\n\nDiet was the area in which the terms were most consistently organized. One widely repeated maxim matches food types to seasons, recommending buds in spring, melon in summer, fruits in autumn and roots in winter. Traditional Chinese medicine has long been associated with this approach: practitioners advocate adjusting one's diet according to the solar terms.\n\nSpecific foods were tied to particular terms. At Start of Spring, the custom of \"biting the spring,\" which involves eating special food like spring pancakes, spring rolls, and carrots, was widespread. During Lesser Fullness of Grain, a customary dietary practice involves incorporating bitter vegetables into meals. In winter, regional differences are clear. In the northern regions, people have a tradition of eating dumplings, while in the south, there is a tradition of eating tangyuan – glutinous sweet rice balls. Before Great Snow, in the north, people begin to pickle meats and fish on the day of the Great Snow solar term, preparing food reserves for the winter.\n\nSource limitations\n\nMuch of the detailed material on specific customs comes from popular, lifestyle and promotional publications, which often repeat one another and seldom cite local fieldwork. The customs above should therefore be read as illustrative examples of how the terms were lived, not as a complete or uniform record. Local practice varied by region, family and period, and the practical role of the terms in farming has declined as modern technological advancements and regional diversity have changed agricultural methods."
    },
    {
      "heading": "Cultural expression: festivals, poetry and proverbs",
      "text": "Festivals tied to particular terms\n\nQingming is the clearest case of a term that also became a festival. The Qingming Festival falls on the first day of the fifth solar term, also called Qingming, and makes it the 15th day after the Spring Equinox. Families visit ancestral graves to clean them and make offerings. The day is also linked to spring outings and kite flying for people to go out for tomb sweeping, spring outings, and kite flying. The holiday's standing owes much to the Tang court: wealthy citizens were reportedly holding overly lavish ancestral ceremonies, and in AD 732 Emperor Xuanzong moved to limit formal ancestral rites to one day a year, Qingming.\n\nSources disagree on how exclusive this status is. One account describes Qingming as the only one that is a solar term and a festival at the same time, while another presents the winter solstice in similar terms, as not only a traditional Chinese Festival but also a solar term. The Dongzhi Festival is marked by regional food customs: dumplings in northern areas and sticky puddings in southern areas. Spring also has ritual observances. In imperial times, emperors held grand ceremonies to welcome spring and pray for a bountiful harvest, and communities used clay oxen in seeding rites. UNESCO's decision notes that the terms are linked to the First Frost Festival of the Zhuang People and the Ritual for the Beginning of Spring in Jiuhua.\n\nPoetry and ballads\n\nThe terms entered oral and literary forms that were easy to memorise. The terms may also be referenced in nursery rhymes, ballads and proverbs. Poems tended to address individual terms rather than the full cycle. Many agricultural proverbs and poems that combine solar terms with ballads have survived to modern times, but systematic and complete sets of twenty-four solar term poems or ballads are extremely rare. The term \"jieqi ge\" (solar terms song) is recorded in a Song-dynasty work on yin-yang numerology and fortune-telling. A Qing-era compilation contains a summary song in which the names of the twenty-four solar terms appear as an acrostic within the poem. Literati also referred to the terms in verse; the poet Tao Yuanming, writing in the early fifth century, alluded to the slow circulation of the stars and solar terms in one of his Drinking poems Tao Yuanming (365-427) said, \"Stars and the solar terms circulate slowly, and the cycle of twelve years has long gone.\"\n\nProverbs and sayings\n\nMany proverbs turn the terms into practical rules of thumb. A widely cited saying, \"Before and after Qingming, sow melons and beans,\" ties the festival to sowing. The name of Guyu (Grain Rain) is traditionally explained through a proverb that rain nourishes all grains. Other sayings warn of late-spring weather: one farming proverb associates the arrival of rain with the beginning of spring and advises early rising, as the spring sowing season begins. Proverbs of this kind carried the calendar's timing in a form that did not require written texts.\n\nRegional and ethnic variation\n\nThe shared framework allowed local adaptation. The calendar is integrated into the Gregorian calendar, it is used widely by communities and shared by many ethnic groups in China. Regional versions of agricultural ballads show different local concerns. For example, a Fujian verse refers to repairing boats and mending nets, adding agricultural tools, olives and pomelos all ripen, while a Guangdong verse concerns lychee harvests and flood and drought control. In this way the terms connected the agricultural calendar with song, verse and speech, giving local communities a common rhythm for work, observance and oral tradition."
    },
    {
      "heading": "Diffusion across East Asia and local variants",
      "text": "The system travelled with the wider lunisolar tradition into the East Asian cultural sphere, where South Korea, Vietnam and Japan were the main recipients. Its names were coined for the climate of the North China Plain, yet peoples in other climates kept using them, and traditional Chinese characters for most of the solar terms are identical across these languages. The shared script did not produce shared pronunciation. Each language reads the same characters through its own phonology, so one term may appear in several forms: Chushu, for example, is also rendered as Shosho in Japanese, Cheoseo in Korean and Xử thử in Vietnamese.\n\nKorea and Vietnam\n\nKorea's traditional calendar followed the Chinese model closely and remained the official reckoning until the late nineteenth century, when the Gregorian system was adopted in 1896. The Korean name for the terms is jeolgi. In Vietnam, the lunisolar calendar also includes twenty-four divisions called tiết, which were used to guide farmers in planting and harvesting. The surviving detail on how Korean and Vietnamese communities scheduled particular tasks by individual terms is less systematic than the Japanese record, so regional specifics should be checked against local scholarship.\n\nJapan\n\nSources differ on when the terms reached Japan. One account places their introduction around the sixth century, while another says Japan adopted the Chinese calendar around the 7th century. Japan's first calendar is traditionally dated to 604 and was a lunar calendar introduced from China via the Korean Peninsula. The most decisive local reform came in the Edo period. Shibukawa Shunkai, an official astronomer, recognized the year has 365 days and found errors in the Chinese lunar calendar. He created a new calendar with 72 kō, divided into 24 sekki, and it was officially adopted in 1685. The calendar was also reordered and renamed to reflect Japan's local climate, flora, and fauna. Several terms still fit the Japanese climate poorly because the system was created in ancient China. The older reckoning, the kyureki, remained in use until 1873, when the Meiji government replaced it with the Gregorian calendar. Farmers and fishermen, however, continued to use the traditional kyureki alongside the enforced Gregorian calendar. Before the switch, Risshun had even been observed as New Year's Day.\n\nTransmission and reinterpretation\n\nTransmission is better understood as selective reuse than as replication. The astronomical definition travelled intact: 0 degree of celestial longitude is the Spring Equinox and every solar term matches a passage of 15 degrees. What changed was the layer of names, seasonal emphasis and associated events. In Japan, scholars adjusted readings and paired the terms with local crops and festivals. Some terms have acquired modern civic meaning there; the spring equinox, for instance, remains a national holiday. The result is less a single standard than a family of related systems, in which the same term can carry different customs, and even different expected weather, from one society to the next."
    },
    {
      "heading": "Observed phenological and climatic shifts",
      "text": "The solar terms were not built as a record of present-day weather. Most of their names were settled in the Han period and describe conditions typical of the Yellow River basin, especially around the Han capital. Each name links a date to an observable event, such as thunder, flowering or crop maturity. The link holds only while the local climate and its seasonal timing stay close to what the names describe. Station records from the second half of the twentieth century onward show that this correspondence has moved in measurable ways.\n\nThe most cited evidence comes from a 2012 analysis by Qian Cheng, Yan Zhongwei and Fu Congbin. It used daily surface air temperature from 549 meteorological stations for 1960–2008 to set temperature thresholds for each climatic term and to date them. The authors found that the spring terms, which fall in the warming part of the annual cycle, have arrived earlier, by more than six days on average and by about fifteen days for Rain Water. The autumn terms, in the cooling part of the cycle, have arrived five to six days later. The same study reports that the mean temperature associated with the Waking of Insects, along with Rain Water and the Beginning of Spring, rose the most across the period 1961–2007 (about 2.2°C for the Waking of Insects).\n\nFour terms with clear phenological content, namely the Waking of Insects, Pure Brightness, Grain Full and Grain in Ear, were found to have advanced in almost all parts of China. In the semi-arid zones of northern China, the advance for the Waking of Insects over 1961–2007 was estimated at 12 to 16 days, the largest of the four. This is the clearest case of the name–event link drifting: a term whose traditional date is around 5 or 6 March in the Gregorian calendar now corresponds to a climatic state that the calendar reaches earlier than the name implies. A 2025 study of 699 stations, covering 1966–2019, reached a similar picture for the early spring period, where temperatures accelerate and precipitation falls back compared with Rain Water.\n\nNot all terms follow the same pattern. A 2024 study of Shanxi Province, using 23 stations for 1960–2019, found that warming was concentrated in the periods from Clear and Bright (Qingming) to Grain Rain (Guyu) and from Minor Snow (Xiaoxue) to Major Cold (Dahan), while sunshine declined in other periods. Precipitation trends in that region were weak and varied from place to place. Such results show that the warming signal is uneven across seasons and provinces, and that a single shift applied to the whole calendar would be misleading.\n\nInterpretation needs more caution than the timing data. The 2012 authors attribute the spring advance and autumn delay mainly to a warming of the whole seasonal cycle linked to global warming, which is a plausible reading of the temperature pattern but rests on correlation rather than a direct test of cause. Because the climatic terms are defined by temperature thresholds, their shifts measure the climate signal, not insect emergence or crop development directly. Direct biological observations are far less dense than station temperature data, so claims about how insects or plants respond should be kept separate from claims about the calendar itself. Differences in station networks, periods and methods also mean that reported magnitudes vary between studies. For this reason, the observed trends are best treated as a regional, statistically supported pattern rather than a uniform national constant."
    },
    {
      "heading": "Scientific and meteorological research",
      "text": "Since the early 2010s, Chinese climate scientists have treated the terms as a usable dataset, not only as a cultural label. A 2012 study by Qian, Yan and Fu set the temperature cut-offs and dates for the climatic terms using a homogenized surface air temperature record from 549 stations, covering 1960–2008 and processed with ensemble empirical mode decomposition (The temperature thresholds and timings of the 24 climatic Solar Terms in China are determined from a homogenized dataset of the surface air temperature recorded at 549 meteorological stations for the period 1960–2008). Its reported results describe a warming shift in the seasonal cycle: the spring-side terms have significantly advanced (by 6-15 days) from the 1960s to the present, while autumn-side timings have delayed by 5-6 days on average. The same study found that four phenology-related terms, Waking of Insects, Pure Brightness, Grain Full and Grain in Ear, have advanced almost everywhere in the country (as much as 20 days in North China). These figures come from a published paper and a press summary of it, so the exact values should be checked against the original article.\n\nPrecipitation has proved harder to link to the terms. A 2026 study of Shanxi Province used records from 23 meteorological stations for 1960–2019 and found that warming was concentrated during Yushui–Qingming and Xiaoxue–Dahan, with sunshine declines across Mangzhong–Xiaoshu and Bailu–Hanlu. In the same study, precipitation trends were weak and spatially variable. The authors coupled this climate analysis with a crop model, which reliably reproduced regional yields and phenology, to test sowing-date options for spring maize. This is one of the few studies that connects the terms directly to agronomic outcomes rather than only to temperature.\n\nOrigin studies use a different set of methods. Earlier work on the geographic origin of the terms relied primarily on historical records, literature review, and field investigation. A 2024 study in Scientific Reports instead used a Solar Terms Typical Meteorological Day (STTMD) method, supplemented by isothermal estimation and clustering analysis. Its results were cross-referenced with historical documents, and the authors concluded that on a larger spatial scale, the Solar Terms originated in the middle and lower reaches of the Yellow River. The study also used millet as a climate-indicator crop to test whether the terms matched local conditions (The figure uses millet as a climate indicator crop to verify the alignment of solar terms with local climate conditions). Its proposed core area is framed as a hypothesis, not a settled finding.\n\nBeyond origin studies, the terms serve as a standard time framework in applied research. The STTMD approach yields twenty-four typical days, obtained via the STTMD method, follow a precise order in the traditional Chinese calendar, with about 15 days between each, and these days can be linked into a hypothetical meteorological year for building simulations. One electricity-load study used the terms to classify days of the year in six northeastern United States states, although these six states are in a different climate zone than China or Southeast Asia, and found that the terms could still sort days usefully. Modern timings are also calculated from astronomical ephemerides rather than observed by hand; one geoscience dataset relied on a JPL solar ephemeris and a numerical root-finding method to fix the moment of each ecliptic longitude (the precise timings of the 24 solar terms primarily rely on the Solar Ephemeris provided by the Jet Propulsion Laboratory (JPL) of the United States).\n\nSeveral limitations affect these analyses. The terms were formed from observations in the Yellow River basin, and their regional fit has been questioned: one review notes that their regional robustness has been increasingly challenged by accumulating observational data in terms of temporal shift and spatial inhomogeneity. Definitions also vary historically. Before 1645, one account notes that the terms were computed by dividing the tropical year evenly into 24 periods, whereas later calendars used positions on the ecliptic, so studies must state which definition they use. Station records are sparse in some regions, and reconstructed historical sequences depend on how texts are interpreted. Attributing observed shifts specifically to warming, rather than to other changes in station networks or observing practice, requires careful statistical treatment that many studies approach with caution."
    },
    {
      "heading": "UNESCO inscription and safeguarding",
      "text": "The system entered UNESCO's Representative List of the Intangible Cultural Heritage of Humanity on 30 November 2016. The decision came during the 11th session of the UNESCO Intergovernmental Committee for the Safeguarding of the Intangible Cultural Heritage in Addis Ababa, Ethiopia. The listed title is \"The Twenty-Four Solar Terms, knowledge in China of time and practices developed through observation of the sun's annual motion,\" and it sits under the intangible cultural heritage framework of the UNESCO 2003 Convention. Chinese officials noted that the inscription was the third China-submitted element in the category covering knowledge and practices concerning nature and universe.\n\nThe nomination file was prepared through a national structure. Coordination came from the Ministry of Culture of the People's Republic of China, the China National Centre for the Safeguarding of Intangible Cultural Heritage and the China Agricultural Museum, and communities, groups and individuals took part at every stage, giving their free, prior and informed consent. Domestic recognition came earlier: the terms were included in the first batch of China's National List of Representative Items of Intangible Cultural Heritage in 2006. Reports on the candidacy also state that, in 2013, officials had to choose among candidate elements, and they settled on the 24 Solar Terms from a list of 14 possibilities.\n\nSafeguarding is organised around a lead institution and a wider network. The China Agricultural Museum acts as the lead body for protection and transmission, working with the Chinese Folklore Society and the representative communities. This has produced a collaborative arrangement combining government leadership, specialised institutions and social participation. Local governments have written the protection of solar-term culture into their own plans; Tiandeng in Guangxi and Quzhou in Zhejiang are cited as examples. A cross-institutional body, the Alliance for the Protection and Transmission of the 24 Solar Terms, has also been described as working to establish the terms as a global cultural emblem.\n\nThe community role is most visible in local customs that carry the calendar from one generation to the next. For instance, traditionally, on the Beginning of Spring, communities would whip a paper ox made under the guidance of local elders. Other transmission activities include festivals and rites tied to particular terms, the household routines of agricultural life, and the teaching of terms in schools and public events, although the specific measures in individual regions vary and are documented unevenly.\n\nAssessments of safeguarding outcomes come mainly from Chinese governmental, museum and state-affiliated sources, and the sources reviewed for this section do not provide independent evaluation of how effectively these measures have sustained local practice. The ratio of institutional programmes to everyday transmission, and the degree to which younger generations use the terms outside ritual or farming contexts, are therefore questions that the available accounts address only partially."
    },
    {
      "heading": "Debates, limitations and open questions",
      "text": "Dating the origins\n\nThe chronology of the system is the most contested point. Researchers agree that the exact origins of the system remain debated in the academic field. Some popular accounts take the idea back to the Shang period (c. 1600–1046 BC), deriving from the need to have a precise climate reference to optimise agricultural production. The evidence cited for the Shang is indirect. Calendar reconciliation with lunar months is documented, since the Shang people used leap months to reconcile differences between the lunar and solar cycles, but this does not by itself show that a set of named solar terms existed. Some scholars therefore place the formal system later, in the Zhou period, when the four main seasonal divisions were established.\n\nDates for the later stages also differ. A full list of names is attested in the Huainanzi, which is usually dated to around 139 BC, and the terms were incorporated officially into the calendar during Emperor Wu's reign in 104 BCE as part of the Taichu Calendar. Other sources describe a longer process: one Chinese account holds that the system was originated along the Yellow River even before the Qin Dynasty and was almost settled down in the Han Dynasty. The 104 BC reform is therefore best described as the point of official adoption, not necessarily the point of invention, and the sources do not agree on how much of the 24-term structure existed before it.\n\nFit to region and climate\n\nThe terms were built from observations in the Yellow River basin, and their names reflect that setting. Because of this, their correspondence with conditions elsewhere is uneven. A 2016 study by Chinese researchers noted that while the basic philosophy of the 24-STs remains valid for the country as a whole, their regional robustness has been increasingly challenged by accumulating observational data in terms of temporal shift and spatial inhomogeneity.\n\nClimate records add a further complication. A study using a homogenised dataset from 549 meteorological stations for 1960–2008 found that the warming tendencies for Rain Water, the Beginning of Spring, and the Waking of Insects are the largest. The same study found that the warming shift affects the different Solar Terms to various extents, more prominently in the spring than in the autumn. Because the terms are defined by temperature thresholds in that analysis, these results describe the terms' climatic meaning and should not be read directly as changes in natural phenology. The authors also noted that for the Beginning of Spring, the temperature during this solar term is still below 0°C in the national mean of recent decades, which shows how far a name can drift from its climatic content.\n\nPhenological trends and causal interpretation\n\nThe four terms linked most closely to biological events, the Waking of Insects, Pure Brightness, Grain Full and Grain in Ear, were found in the same study to have advanced almost everywhere. This is consistent with a broader pattern in which shifts toward earlier seasonal activity are widespread; however, responses of insect phenology to warming are often more complex. Other research reports that many species have prolonged their activity periods; others have shown delays, so the Waking of Insects should not be treated as a simple clock.\n\nSeveral limits apply. The records describe timing relative to thresholds, not direct observations of insects or plants. The station network and the homogenisation methods shape the results. And the attribution of observed shifts to warming, rather than to urbanisation, land use or changes in observer practice, requires further analysis than the available sources provide. Statements about causes are therefore tentative.\n\nTranslation and terminology\n\nNo single English rendering is settled. One review notes that there is a great debate on how to translate the 24 solar terms at home and abroad, and no definitive version exists. Two systems have emerged, the Commercial Press edition and the Astronomical Society edition, and different dictionaries and websites use different wording for the same term. Readers comparing sources should check the Chinese characters before equating two English names.\n\nThe \"fifth great invention\" label\n\nThe phrase \"China's fifth great invention\" is widely repeated, and it places the terms alongside papermaking, printing, gunpowder and the compass. Many sources that use it are official, media or tourism outlets, and they describe the terms in praise rather than in evaluative terms. The label is therefore better understood as promotional framing than as an assessment made by a scholarly body. It also obscures the fact that the terms are a local calendrical system whose usefulness depends on the region and period in question.\n\nOpen questions\n\nSeveral questions remain unresolved: how early the terms were formalised; how far the system was used outside the central plains before the Han; how the historical correspondence between names and conditions should be revised for modern climates; and whether the regional and temporal inconsistencies documented in recent studies can be reconciled with the terms' original purpose. Each of these depends on sources and methods that are still being developed."
    }
  ],
  "links": [
    "sun",
    "moon",
    "weather",
    "china",
    "intangible-cultural-heritage",
    "unesco",
    "chinese-calendar",
    "ritual",
    "climate-change",
    "south-korea",
    "vietnam",
    "japan",
    "chinese-characters",
    "yellow-river"
  ],
  "sources": [
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    },
    {
      "title": "China's ancient ‘24 Solar Terms’ given UN Cultural Heritage status - CGTN",
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    },
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      "url": "https://www.globaltimes.cn/page/202601/1353750.shtml"
    },
    {
      "title": "China's \"24 Solar Terms\" inscribed on UNESCO intangible cultural heritage list - Xinhua",
      "url": "http://www.xinhuanet.com/english/2016-11/30/c_135870911.htm"
    },
    {
      "title": "Chinese 24 Solar Terms: The Chinese wisdom of dividing time - Chinadaily.com.cn",
      "url": "https://global.chinadaily.com.cn/a/201810/26/WS5bd2c96ba310eff303284d41.html"
    },
    {
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    },
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      "url": "https://www.scirp.org/pdf/ojapps_2023120714313942.pdf"
    },
    {
      "title": "China's 24 Solar Terms",
      "url": "https://www.cma.gov.cn/en2014/20150311/20170119/201701/t20170119_388239.html"
    }
  ],
  "license": "https://creativecommons.org/licenses/by/4.0/"
}