Editing Solar term (section)

{{Short description|Any of 24 periods of traditional East Asian lunisolar calendars}}
[[File:24solarterms.png|thumb|The 24 solar terms with labels in Japanese]]
{{Infobox Chinese
| title = (Twenty-four) solar terms
| t = (二十四)節氣
| s = (二十四)节气
| j = (ji<sup>6</sup> sap<sup>6</sup> sei<sup>3</sup>) zit<sup>3</sup> hei<sup>3</sup>
| poj = (jī-cha̍p-sì) cheh-khùi
| p = (èrshísì) jiéqì
| w = (erh-shih-ssŭ) chieh-chi
|mi=({{IPAc-cmn|er|4|.|shi|2|.|si|4}}) {{IPAc-cmn|j|ie|2|.|q|i|4}}
}}
{{Solar terms}}
A '''solar term''' (or '''''jiéqì''''', {{lang-zh|t=節氣|s=节气}}) is any of twenty-four periods in traditional [[Chinese calendar|Chinese]] [[lunisolar calendar]]s that matches a particular astronomical event or signifies some natural phenomenon.<ref>{{cite web|url=https://www.asia-home.com/china/solterms.php|title=24 Chinese Feasts (Jiéqì, 节气), equivalent to the 24 Chinese Solar Terms|work=Chinese calendar|publisher=asia-home.com}}</ref> The points are spaced 15° apart along the [[ecliptic]]<ref>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.</ref> 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 [[Intercalation (timekeeping)|intercalary months]];<ref>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 {{lang|zh|歲中閏月法}} lit. "midpoint intercalating system".</ref> which month is repeated depends on the position of the sun at the time.

According to the ''[[Book of Documents]]'', the first determined term was [[Dongzhi (solar term)|Dongzhi]] (Winter Solstice) by [[Duke of Zhou|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 {{ill|tugui|ja|土圭|lt=''tǔguī''}} ({{lang|zh|土圭}}).<ref>{{Cite book|title=Book of Documents}}</ref> Then four terms of seasons were set, which were soon evolved as eight terms; not until the Taichu Calendar of 104 BC were all twenty-four solar terms officially included in the Chinese calendar.<ref>{{Cite book|title=Book of Han|last=Ban|first=Gu}}</ref>

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 {{ill|Pentad (calendar)|lt=pentads|zh|七十二候}} ({{lang-zh|c=候|p=hòu|labels=no}}), so there are 72 pentads in a year, consisting of five, rarely six, days. Most of them are named after [[phenology|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.<ref>[http://koyomi8.com/reki_doc/doc_0702.htm 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.</ref> 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]].<ref>{{cite web |title=UNESCO – The Twenty-Four Solar Terms, knowledge in China of time and practices developed through observation of the sun's annual motion |url=https://ich.unesco.org/en/RL/the-twenty-four-solar-terms-knowledge-in-china-of-time-and-practices-developed-through-observation-of-the-suns-annual-motion-00647 |website=ich.unesco.org |access-date=9 March 2021 |language=en}}</ref>