24 Solar Terms Explained: Dates, History & UNESCO

What Are the 24 Solar Terms?

The 24 solar terms (二十四节气, èrshísì jiéqì) are a way of dividing the year into twenty-four seasons of roughly fifteen days each, set by the Sun's apparent position along its annual path rather than by the Moon. Astronomically, the Sun's yearly motion across the sky — the ecliptic — is divided into 24 equal segments of 15 degrees of solar longitude each. Every time the Sun completes another 15 degrees of that circle, a new solar term begins.

The reference point for this longitude is the vernal (spring) equinox, conventionally set at 0°. From there the terms follow in 15-degree steps: 0°, 15°, 30°, and so on through the whole circle. Three of these reference points are easy to feel even without any astronomy: at the spring and autumn equinoxes, day and night are close to equal in length; daylight is longest in the northern hemisphere around the summer solstice and shortest around the winter solstice.

Two things are easy to misunderstand. First, the solar terms are a solar system: they track the Sun, so their Gregorian dates stay stable from year to year, drifting by only a day or two. They are not tied to the Moon's phases, and they should not be confused with lunar months, which are about 29.5 days long and follow the Moon. Second, the system is not one uniform list of "seasonal nodes." It is a blend of two interlaced groups — the 12 major solar terms and the 12 minor solar terms — and getting that distinction right matters for understanding the traditional Chinese calendar (see below).

The 二十四节气 have been used for more than two millennia in China, first for agriculture and later as a shared framework for festivals, language, and daily life. The system originated in the Yellow River basin of central China and later spread to Japan, the Korean Peninsula, and Vietnam, where each culture gave it its own local flavor. Their enduring importance was recognized in 2016 when UNESCO added the twenty-four solar terms to its Representative List of the Intangible Cultural Heritage of Humanity.

Origin and History

The solar terms did not appear all at once. They grew out of centuries of careful observation of the Sun, and the earliest step was the most obvious one: watching the year's two turning points, the summer and winter solstices.

The oldest written anchors come from the late Shang period. The oracle-bone inscriptions of the last nine Shang kings (roughly 1324–1122 bc) record regular religious services held on the summer and winter solstice days. These are the earliest confirmed observations of the seasonal axis around which the whole later system turns. The equinoxes, by contrast, are not attested in those early records, and their addition belongs to a later stage of the system's development.

From the two solstices, the sky-watchers added the two equinoxes, then the four "beginnings" of each season (the 立 terms for spring, summer, autumn, and winter). Only after those cardinal anchors were in place was the year further subdivided into the full set of twenty-four named terms.

The complete ordered set of the twenty-four names — essentially the same names used today — appears in the Han-era philosophical collection Huainanzi (淮南子), in its chapter on astronomical teachings. Chinese solar-term scholarship treats this as the first full written list of the system, matching what remained in use in later centuries. The precise year the text was presented to the court is not firmly established in the sources relied on here, so this guide does not assert one; what is well supported is that the full list was fixed and written down by the Han period.

Refining when each term actually happens took a long time. A major milestone came in the late thirteenth century. Between 1276 and 1281 the astronomers Guo Shoujing and Wang Xun compiled the Shoushi Calendar (授时历), which set the length of the tropical year at 365.2425 days — the same value as the mean Gregorian year used in the Western calendar. Getting solar-term dates this accurately, without telescopic instruments, was a real achievement of observational astronomy.

Over the dynasties the system's terminology and astronomical basis were steadily refined, and the underlying idea spread well beyond the Yellow River basin. Alongside its use across China, the system reached the Korean Peninsula and Vietnam, and it was taken up in Japan around the sixth century. How long ago the system began is stated somewhat differently by different, mutually consistent authorities: some trace it over 2,500 years, others over 2,000 years. This guide therefore describes it simply as a system more than two millennia old, keeping to what the sources support.

How the Solar Terms Are Calculated

The calculation is a pure piece of solar geometry. Take the Sun's apparent annual circle across the sky and divide it into 24 arcs of 15 degrees of solar longitude each. The start of each new 15-degree arc is the moment a new solar term begins. The arc that opens at 0° is the spring equinox, the next 15° opens the following term, and so on around the full circle.

Because the terms are fixed to the Sun, not the Moon, each one lasts roughly 15 days (365¼ days in a year divided by 24). The dates drift by only about a day or two from year to year, shifting with leap years and the exact astronomical instant.

Today the precise moment of each term — to the day, hour, and minute — is computed from astronomical ephemerides. Authoritative reference tables, such as the ones published by the Hong Kong Observatory, derive their values from ephemerides issued by the HM Nautical Almanac Office (United Kingdom) and the US Naval Observatory, and state them in China Standard Time (UTC+8), which the Observatory gives as Hong Kong Time. The exact instant therefore depends on the year, on the observer's time zone, and on the astronomical convention used; the approximate calendar windows shown throughout this guide are reading aids, not fixed dates.

One consequence of staying close to the Sun's real motion: Earth does not orbit at an even speed. Because the orbit is slightly elliptical, Earth is closest to the Sun in early January and is moving fastest near that point. As Kepler's second law predicts, the Sun's longitude then advances quickly, so each 15-degree term around January–February is a little shorter than the average, while near aphelion in July, when Earth is slowest, each term stretches a little longer.

Major (中气) and Minor (节气) terms

In the astronomical tradition summarized by the Hong Kong Observatory, the system comprises 12 major solar terms and 12 minor solar terms interlaced with one another.

• The 12 major terms are the ones that anchor the months of the traditional lunisolar calendar. In solar-longitude order they are: 雨水 (spring showers), 春分 (vernal equinox), 谷雨 (corn rain), 小满 (corn forms), 夏至 (summer solstice), 大暑 (great heat), 处暑 (end of heat), 秋分 (autumnal equinox), 霜降 (frost), 小雪 (light snow), 冬至 (winter solstice), and 大寒 (severe cold).
• The 12 minor terms fall between the major ones. They are: 立春 (spring commences), 惊蛰 (insects waken), 清明 (bright and clear), 立夏 (summer commences), 芒种 (corn on ear), 小暑 (moderate heat), 立秋 (autumn commences), 白露 (white dew), 寒露 (cold dew), 立冬 (winter commences), 大雪 (heavy snow), and 小寒 (moderate cold).

This is the reverse of a common popular mistake. The word 节气 (jiéqì) is the general name of the whole system, and the "节" (jié) terms here are the minor ones; the major terms are the 中气 (zhōngqì). So the four solstices and equinoxes — 春分, 夏至, 秋分, 冬至 — are all major (中气) terms, while the four "beginnings of the season" (立春, 立夏, 立秋, 立冬) are minor (节气) terms. An older description of the system is the traditional division of each season into three 节气 (Setsu) and three 中气 (Chū), alternating with one another.

The major/minor split matters because the 中气 do real work in the calendar. Each lunar (agricultural) month of the traditional Chinese calendar contains one major solar term; a lunar month that contains no major term is treated as an intercalary, or leap, month of the preceding month. Over 19 tropical years there are 228 major solar terms and 235 synodic months, so seven lunar months have no major term and become leap months. It is for this reason — keeping the lunar months aligned with the seasons — that the solar terms were, and still are, needed at all.

The Four Seasons and Their Terms

In everyday use the twenty-four terms are grouped into four seasons of six terms each, in calendar order from the beginning of spring. Each season opens with its 立 (lì, "beginning") term, reaches an extreme in the middle (a solstice 至, an equinox 分, or a peak of heat 暑 or cold 寒), and closes on a transitional term.

• Spring (春季, chūnjì) — 立春 to 谷雨: opens with 立春 (Start of Spring) in early February, the traditional start of the agricultural year; runs through warming rain and the awakening of insects to 谷雨 (Grain Rain) in late April.
• Summer (夏季, xiàjì) — 立夏 to 大暑: begins in early May, peaks at 夏至 (Summer Solstice) around the year's longest day, and closes with the most intense heat of the year at 大暑 (Major Heat) in late July.
• Autumn (秋季, qiūjì) — 立秋 to 霜降: opens in early August, passes through the autumn equinox around equal day and night, and ends with 霜降 (Frost Descent) in late October as the first frost closes the growing season.
• Winter (冬季, dōngjì) — 立冬 to 大寒: begins in early November, reaches the shortest day at 冬至 (Winter Solstice) in late December, and closes on 大寒 (Major Cold) in late January before the cycle turns back to 立春.

Because the astronomical year does not line up neatly with the calendar's month boundaries, the seasonal labels here are meant as daylight- and temperature-sensitive guides to the solar year, not as fixed weather forecasts for any one place. How each term actually feels still depends strongly on latitude, coast, and altitude — a point the modern-use section returns to below.

Complete Table of the 24 Solar Terms

The table lists the terms in calendar order (立春 through 大寒), which is how they appear in the Chinese seasonal cycle. The longitude column uses the astronomical convention that sets the spring equinox at 0° and counts forward through the year, matching the Hong Kong Observatory. Terms marked 中气 are the 12 major (month-anchoring) terms; those marked 节气 are the 12 minor terms. Approximate calendar windows are reading aids drawn from the Oriens solar-term data set; exact instants come from the astronomical tables, not from these windows.

Note the two conventions in one place. The longitude zero is the spring equinox (春分 at 0°), which is why the cycle's numbers do not begin at #1: the two "0°" and "15°" terms (春分 and 清明) sit in the middle of the spring season, while 立春 (Start of Spring), found by counting forward from the equinox, carries longitude 315°. The table's row order, by contrast, follows the year's start at 立春. Keeping these two frames distinct avoids a common source of confusion.

Every individual term also has its own page in the Oriens guide set, with the full astronomical position, pinyin, and seasonal context — for example Start of Spring and Winter Solstice. A compact date reference lives at the 24 Solar Terms reference table, and a short definition appears on What Is a Solar Term?.

UNESCO Intangible Cultural Heritage (2016)

In November 2016 the intergovernmental committee of UNESCO inscribed the system on the Representative List of the Intangible Cultural Heritage of Humanity, at the committee's eleventh session. The official element name is The Twenty-Four Solar Terms, knowledge in China of time and practices developed through observation of the sun's annual motion. The wording of the inscription is worth reading closely: it frames the solar terms not as a mere calendar grid but as knowledge of time and practices built up through observing the sun. The 2016 decision is recorded as Decision 11.COM 10.B.6 on the UNESCO page for the element.

That recognition carries two messages. It acknowledges the astronomical accuracy of the system — that careful observation of the sun, gathered over more than two millennia, could produce a stable and practical division of the year. And it acknowledges the whole cultural ecosystem around the terms: the seasonal proverbs, festivals, foods, and daily habits that grew up around each one. The heritage listed is as much about how people live with the seasons as about the positions of the sun.

Solar Terms and Traditional Festivals

Several East Asian festivals are anchored to specific solar terms, and they illustrate how an astronomical grid became a social calendar.

Qingming (清明). The fifth term, Pure Brightness (清明, Qīngmíng), falls in early April and is both a solar term and a major festival in which families visit and tend ancestral graves and enjoy spring outings. In mainland China, Qingming is one of the official public holidays.

Winter Solstice (冬至, Dōngzhì). The twenty-second term marks the winter solstice, the shortest day of the northern year. Across East Asia it has long been observed as an important day of family gathering and shared food — dumplings in parts of the north, sweet glutinous rice balls in the south. Dōngzhì is a significant traditional festival, but it is not among mainland China's official statutory public holidays the way Qingming is. (Holiday rules can differ in Hong Kong, Macau, and Taiwan; this guide does not generalize legal holiday status beyond mainland China.)

Lunar New Year proximity. The Lunar New Year (春节, Chūnjié) is fixed by the lunisolar calendar and therefore moves through late January and February from year to year, so it always lands close to — but not on — the Start of Spring (立春) solar term. The two should not be conflated: one is a lunar-month festival, the other a solar-term marker.

As a generalization, the solar terms set a calendar the festivals decorate. Qingming and Dōngzhì show the pattern: the astronomical framework provides the fixed seasonal points, and each regional tradition decides how to mark them.

Modern Relevance

The solar terms are not a museum piece. They remain woven into calendars, weather interfaces, schools, and everyday language across East Asia. Three uses are especially visible.

Calendars and weather services. Chinese calendars and weather apps commonly display the current solar term alongside the standard date, giving a read on the expected seasonal pattern rather than the single day's forecast. The system works as a coarse long-range seasonal guide: it says "the hottest stretch of summer has arrived" or "frost season is beginning," which is useful even if exact weather never matches a label everywhere.

Education and a teaching mnemonic. Chinese schoolchildren commonly learn the names of the terms through a short memorable rhyme (节气歌, jiéqì gē) that strings the twenty-four names together in order. The rhyme is a teaching aid that helps memorization; it is part of popular education, not part of the astronomical definition of the terms, and it is therefore treated here as cultural material rather than as a scientific statement.

Cultural identity and regional adaptation. Beyond China, the system was adopted in Japan (二十四節気, nijūshi sekki), on the Korean Peninsula, and in Vietnam, where each culture adapted it to its own climate and agriculture while keeping the same solar framework. For this reason a single term can mean "start of spring" at the astronomical level yet be experienced very differently in a subtropical city, a high plateau, or a northern plain.

Regional nuance, health, and limits

Two honest limits keep this guide from overreach. First, the solar terms describe a solar year designed in and for central China's Yellow River climate. They are an excellent framework for situating yourself in the solar year, but they are not an individualized forecast: how a given term feels depends on latitude, altitude, and weather, and no blanket statement about crops or "the season is X here" holds everywhere.

Second, the system's vocabulary of heat and cold, yin and yang, and seasonal habits is historical cosmology and cultural practice, not modern medical advice. Traditional sayings about what to eat or how to live in each term reflect centuries of seasonal wisdom, but this guide deliberately does not make health claims about specific diets, organs, or treatments, and readers should not treat seasonal folklore as a prescription. The astronomical facts above are what is verified here; the seasonal proverbs are presented as culture, not as science or medicine.

For the astronomy behind any single term, see the individual solar-term pages and the entity overview of the Solar Terms section; the complete guide collects the twenty-four terms with their seasonal context.