Solar term

A solar term (or jieqi, simplified Chinese: 节气; traditional Chinese: 節氣) is any of twenty-four periods in traditional Chinese lunisolar calendars that matches a particular astronomical event or signifies some natural phenomenon.^[1] The points are spaced 15° apart along the ecliptic^[2] and are used by lunisolar calendars to stay synchronized with the seasons, which is crucial for agrarian societies. The solar terms are also used to calculate intercalary months;^[3] which month is repeated depends on the position of the sun at the time.

The 24 solar terms

(Twenty-four) solar terms
Traditional Chinese	(二十四)節氣
Simplified Chinese	(二十四)节气
Transcriptions Standard Mandarin Hanyu Pinyin (èrshísì) jiéqì Wade–Giles (erh-shih-hsi) chieh-chi IPA [tɕjě.tɕʰî] Yue: Cantonese Jyutping (ji6 sap6 sei3) zit3 hei3 Southern Min Hokkien POJ (jī-si̍p-sù) cheh-khùi

Solar term

Term	Longitude	Dates
Lichun	315°	4–5 February
Yushui	330°	18–19 February
Jingzhe	345°	5–6 March
Chunfen	0°	20–21 March
Qingming	15°	4–5 April
Guyu	30°	20–21 April
Lixia	45°	5–6 May
Xiaoman	60°	21–22 May
Mangzhong	75°	5–6 June
Xiazhi	90°	21–22 June
Xiaoshu	105°	7–8 July
Dashu	120°	22–23 July
Liqiu	135°	7–8 August
Chushu	150°	23–24 August
Bailu	165°	7–8 September
Qiufen	180°	23–24 September
Hanlu	195°	8–9 October
Shuangjiang	210°	23–24 October
Lidong	225°	7–8 November
Xiaoxue	240°	22–23 November
Daxue	255°	7–8 December
Dongzhi	270°	21–22 December
Xiaohan	285°	5–6 January
Dahan	300°	20–21 January

According to the Book of Documents, the first determined term was Dongzhi (Winter Solstice) by Dan, the Duke of Zhou, while he was trying to locate the geological center of the Western Zhou dynasty, by measuring the length of the sun's shadow on an ancient type of sundial called tǔguī [ja] (土圭).^[4] Then four terms of seasons were set, which were soon evolved as eight terms; until 104 BC in the book Taichu Calendar, the entire twenty-four solar terms were officially included in the Chinese calendar.^[5]

Because the Sun's speed along the ecliptic varies depending on the Earth-Sun distance, the number of days that it takes the Sun to travel between each pair of solar terms varies slightly throughout the year, but it is always between 15 and 16 days. Each solar term is divided into three pentads [zh] (候; hòu), so there are 72 pentads in a year. Each pentad consists of five, rarely six, days, and are mostly named after phenological (biological or botanical) phenomena corresponding to the pentad.

Solar terms originated in China, then spread to Korea, Vietnam, and Japan, countries in the East Asian cultural sphere. Although each term was named based on the seasonal changes of climate in the North China Plain, peoples living in the different climates still use it without changes.^[6] This is exhibited by the fact that traditional Chinese characters for most of the solar terms are identical.

On December 1, 2016, the solar terms were listed by UNESCO as an Intangible Cultural Heritage.^[7]

Numbering

The even solar terms (marked with "Z", for Chinese: 中氣) are considered the major terms, while the odd solar terms (marked with "J", for Chinese: 節氣) are deemed minor. The year starts with Lichun (J1) and ends with Dahan (Z12).^[8]

Multilingual list

Sun's ecliptic longitude	Chinese name[9]	Korean name[10]	Vietnamese name	Japanese name	Ryukyuan (Okinawan) name	English name (Hong Kong Observatory)[11]	English name (Beijing 2022 Winter Olympics)[12]	Gregorian Date[13] (± 1 day)	Reference for Month Intercalating	Chinese zodiac & Earthly Branch of Month	Corresponding Western astrological sign
315°	立春 lìchūn	立春 (입춘/립춘) ipchun/ripchun	Lập xuân (立春)	立春（りっしゅん） risshun	立春（りっしゅん） risshun	Spring commences	Beginning of Spring	Feb 4	1st month initial	Tiger (虎) Yín (寅)	Aquarius
330°	雨水 yǔshuǐ[14]	雨水 (우수) usu	Vũ thủy (雨水)	雨水（うすい） usui	雨水（うしー） ushii	Rain water	Rain Water	Feb 19	1st month midpoint		Pisces
345°	驚蟄 (惊蛰) jīngzhé[15]	驚蟄 (경칩) gyeongchip	Kinh trập (驚蟄)	啓蟄（けいちつ） keichitsu	驚く（うどぅるく） uduruku; 驚くー（おどるくー） udurukuu; 虫驚（むしうどぅるく） mushi'uduruku	Insects waken	Awakening of Insects	Mar 6	2nd month initial	Rabbit (兔) Mǎo (卯)
0°	春分 chūnfēn	春分 (춘분) chunbun	Xuân phân (春分)	春分（しゅんぶん） shunbun	春分（すんぶん） sunbun	Vernal equinox	Spring Equinox	Mar 21	2nd month midpoint		Aries
15°	清明 qīngmíng[16]	淸明 (청명) cheongmyeong	Thanh minh (清明)	清明（せいめい） seimei	清明（しーみー） shiimii	Bright and clear	Pure Brightness	Apr 5	3rd month initial	Dragon (龍) Chén (辰)
30°	穀雨 (谷雨) gǔyǔ[17]	穀雨 (곡우) gogu	Cốc vũ (穀雨)	穀雨（こくう） kokuu	穀雨（くくー） kukuu	Corn rain	Grain Rain	Apr 20	3rd month midpoint		Taurus
45°	立夏 lìxià	立夏 (입하/립하) ipha/ripha	Lập hạ (立夏)	立夏（りっか） rikka	立夏（りっかー） rikkaa	Summer commences	Beginning of Summer	May 6	4th month initial	Snake (蛇) Sì (巳)
60°	小滿 (小满) xiǎomǎn	小滿 (소만) soman	Tiểu mãn (小滿)	小満（しょうまん） shōman	小満（すーまん） suuman	Corn forms	Grain Buds	May 21	4th month midpoint		Gemini
75°	芒種 (芒种) mángzhòng	芒種 (망종) mangjong	Mang chủng (芒種)	芒種（ぼうしゅ） bōshu	芒種（ぼーすー） boosuu	Corn on ear	Grain in Ear	Jun 6	5th month initial	Horse (馬) Wǔ (午)
90°	夏至 xiàzhì	夏至 (하지) haji	Hạ chí (夏至)	夏至（げし） geshi	夏至（かーちー） kaachii	Summer solstice	Summer Solstice	Jun 21	5th month midpoint		Cancer
105°	小暑 xiǎoshǔ	小暑 (소서) soseo	Tiểu thử (小暑)	小暑（しょうしょ） shōsho	小暑（くーあちさ） kuu'achisa	Moderate heat	Minor Heat	Jul 7	6th month initial	Goat (羊) Wèi (未)
120°	大暑 dàshǔ	大暑 (대서) daeseo	Đại thử (大暑)	大暑（たいしょ） taisho	大暑（うーあちさ） uu'achisa	Great heat	Major heat	Jul 23	6th month midpoint		Leo
135°	立秋 lìqiū	立秋 (입추/립추) ipchu/ripchu	Lập thu (立秋)	立秋（りっしゅう） risshū	立秋（りっすー） rissuu	Autumn commences	Beginning of Autumn	Aug 8	7th month initial	Monkey (猴) Shēn (申)
150°	處暑 (处暑) chǔshǔ	處暑 (처서) cheoseo	Xử thử (處暑)	処暑（しょしょ） shosho	処暑（とぅくるあちさ） tukuru'achisa	End of heat	End of Heat	Aug 23	7th month midpoint		Virgo
165°	白露 báilù	白露 (백로) baengno	Bạch lộ (白露)	白露（はくろ） hakuro	白露（ふぁくるー） fakuruu	White dew	White Dew	Sep 8	8th month initial	Rooster (雞) Yǒu (酉)
180°	秋分 qiūfēn	秋分 (추분) chubun	Thu phân (秋分)	秋分（しゅうぶん） shūbun	秋分（すーぶん） suubun	Autumnal equinox	Autumn Equinox	Sep 23	8th month midpoint		Libra
195°	寒露 hánlù	寒露 (한로) hallo	Hàn lộ (寒露)	寒露（かんろ） kanro	寒露（かんるー） kanruu	Cold dew	Cold Dew	Oct 8	9th month initial	Dog (狗) Xū (戌)
210°	霜降 shuāngjiàng	霜降 (상강) sanggang	Sương giáng (霜降)	霜降（そうこう） sōkō	霜降（しむくだり） shimukudari	Frost	Frost's Descent	Oct 23	9th month midpoint		Scorpio
225°	立冬 lìdōng	立冬 (입동/립동) ipdong/ripdong	Lập đông (立冬)	立冬（りっとう） rittō	立冬（りっとぅー） rittuu	Winter commences	Beginning of Winter	Nov 7	10th month initial	Pig (豬) Hài (亥)
240°	小雪 xiǎoxuě	小雪 (소설) soseol	Tiểu tuyết (小雪)	小雪（しょうせつ） shōsetsu	小雪（くーゆち） kuuyuchi	Light snow	Minor Snow	Nov 22	10th month midpoint		Sagittarius
255°	大雪 dàxuě	大雪 (대설) daeseol	Đại tuyết (大雪)	大雪（たいせつ） taisetsu	大雪（うーゆち） uuyuchi	Heavy snow	Major Snow	Dec 7	11th month initial	Rat (鼠) Zǐ (子)
270°	冬至 dōngzhì	冬至 (동지) dongji	Đông chí (冬至)	冬至（とうじ） tōji	冬至（とぅんじー） tunjii	Winter solstice	Winter Solstice	Dec 22	11th month midpoint		Capricorn
285°	小寒 xiǎohán	小寒 (소한) sohan	Tiểu hàn (小寒)	小寒（しょうかん） shōkan	小寒（すーかん） suukan	Moderate cold	Minor Cold	Jan 6	12th month initial	Ox (牛) Chǒu (丑)
300°	大寒 dàhán	大寒 (대한) daehan	Đại hàn (大寒)	大寒（だいかん） daikan	大寒（でーかん） deekan	Severe cold	Major Cold	Jan 20	12th month midpoint		Aquarius

Chinese mnemonic song

The "Song of Solar Terms" (simplified Chinese: 节气歌; traditional Chinese: 節氣歌; pinyin: jiéqìgē) is used to ease the memorization of jieqi:

Traditional Chinese 春雨驚春清穀天 夏滿芒夏暑相連 秋處露秋寒霜降 冬雪雪冬小大寒 每月兩節不變更 最多相差一兩天 上半年來六、廿一 下半年是八、廿三

Simplified Chinese 春雨惊春清谷天 夏满芒夏暑相连 秋处露秋寒霜降 冬雪雪冬小大寒 每月两节不变更 最多相差一两天 上半年来六、廿一 下半年是八、廿三

Pinyin chūn yǔ jīng chūn qīng gǔ tiān, xià mǎn máng xià shǔ xiāng lián, qiū chù lù qiū hán shuāng jiàng, dōng xuě xuě dōng xiǎo dà hán. měi yuè liǎng jié bù biàn gēng, zùi duō xiāng chā yī liǎng tiān shàng bàn nián lái liù, niàn yī xià bàn nián shì bā, niàn sān

The first four lines provides a concise version of the names of the 24 jieqi. The last four lines provide some rules of thumb about the Gregorian dates of jieqi, namely:

• Two jieqi per month;
• Gregorian dates are off by one or two days at most;
• In the first half of the year, jieqi happens around the 6th and 21st day of each (Gregorian) month;
• In the second half of the year, jieqi happens around the 8th and 23rd day of each (Gregorian) month.

Determination

See also: Ecliptic § Sun's apparent motion

Chart with the solar terms and their Vietnamese names

The modern definition using ecliptic longitudes, introduced by the Shixian calendar, is known as 定气法 (dìng qì fǎ, 'steady term method'). Under this method, the determination of solar terms is similar to the astronomical determination of the special cases of equinox and solstice dates, with different ecliptic longitudes to solve for. One can start with an approximation and then perform a correction using the anomalies and mean motion of the sun.^[18] The JPL Horizons On-Line Ephemeris System may be used to query for exact times of solar terms.

The older method is known as 平气法 (píng qì fǎ, 'equal term method') and simply divides the tropical year into 24 equal parts.

Regional note

In Japan, the term Setsubun (節分) originally referred to the eves of Risshun (立春, 315°, the beginning of Spring), Rikka (立夏, 45°, the beginning of Summer), Risshū (立秋, 135°, the beginning of Autumn), and Rittō (立冬, 225°, the beginning of Winter), but currently mostly refers to the day before Risshun. The name of each solar term also refers to the period of time between that day and the next solar term, or 1/24th of a year.

See also

• Chinese calendar
• Korean calendar
• Japanese calendar
• Vietnamese calendar

References

1. "24 Chinese Feasts (Jiéqì, 节气), equivalent to the 24 Chinese Solar Terms". Chinese calendar. asia-home.com.
2. Until 1644 (Chinese Empire and its tributary states) or 1844 (Japan) a period of time of the solar year itself had been equally divided instead of the spatial zodiac.
3. When a lunar month's end does not reach a midpoint of the solar terms, it is regarded as the last month's intercalary one instead of the true "next" month. It is called 歲中閏月法 lit. "midpoint intercalating system".
4. Book of Documents.
5. Ban, Gu. Book of Han.
6. なぜずれる？　二十四節気と季節感 (Why off-point? -solar terms and our real feeling of the seasons) Maritime Japan, for example, comparing the climate of Taiyuan with that of Tokyo and Kyoto: on Japanese islands differences in seasonal gap lengths are the main problem. In subtropical or tropical regions including southern China climate difference is more serious.
7. "UNESCO – The Twenty-Four Solar Terms, knowledge in China of time and practices developed through observation of the sun's annual motion". ich.unesco.org. Retrieved 9 March 2021.
8. Aslaksen, Helmer. "When is Chinese New Year?" (PDF). Archived from the original (PDF) on 13 March 2009. Retrieved 27 July 2019.
9. Simplified Chinese characters are shown in parentheses if they differ from the Traditional Chinese characters.
10. Hangul are shown in parentheses. For Hangul and romanisation, where the pronunciation differs between South Korea and North Korea, the South Korean pronunciation is given first before the slash, followed by the North Korean pronunciation.
11. "The 24 Solar Terms". Hong Kong Observatory.
12. "二十四节气上了北京冬奥开幕式，牛！".
13. Date can vary within a ±1 day range.
14. the Yushui and Jingzhe have been exchanged by Liu Xin in Han dynasty.
15. the Jingzhe and Yushui have been exchanged by Liu Xin in Han dynasty.
16. the Qingming and Guyu have been exchanged by Liu Xin in Han dynasty.
17. the Guyu and Qingming have been exchanged by Liu Xin in Han dynasty.
18. "Determination of Equinox and Solstice Dates". farside.ph.utexas.edu.

External links

• 24 Solar Terms calculator
• 24 Solar Terms – Hong Kong Observatory
• Twenty Four Solar Terms and Their Customs in China
• Chinese calendar with upcoming solar terms in current year
• 24 Sekki – NAOJ > ECO > Glossary >
• Twenty-four Solar Terms and meaning
• Date and time of Solar Terms
• The 24 Solar Terms