A solar term is any of 24 points in traditional East Asian lunisolar calendars that matches a particular astronomical event or signifies some natural phenomenon. The points are spaced 15° apart along the ecliptic 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 in East Asian calendars; which month is repeated depends on the position of the sun at the time.
Solar terms originated in China, then spread to Korea, Vietnam, and Japan. This is exhibited by the fact that traditional Chinese, Hanja, and Kanji characters for most of the solar terms are identical.
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. Each solar term is divided into three pentads (候 hou), so there are 72 pentads in a year. Each pentad consists of five, rarely six, days, and are mostly named after biological or botanical phenomena corresponding to the pentad.
List of solar terms
|315°||start of spring||立春
|Aquarius||Feb 19||more rain than snow|
|345°||awakening of insects||驚蟄 (惊蛰)
|Aquarius||Mar 6||lit. awakening of hibernating insects. See the note at #Solar term.|
|Pisces||Mar 21||lit. spring division (or center)|
|15°||clear and bright||清明
|Pisces||Apr 5||time for tending graves|
|30°||grain rain||穀雨 (谷雨)
|Aries||Apr 20||lit. Cereal grain rain: rain helps grain grow|
|45°||start of summer||立夏
|60°||grain full||小滿 (小满)
|Taurus||May 21||grains are plump|
|75°||grain in ear||芒種 (芒种)
|Taurus||Jun 6||lit. awns (beard of grain) grow|
|Gemini||Jun 21||lit. summer extreme (of sun's height)|
|135°||start of autumn||立秋
|150°||limit of heat||處暑 (处暑)
|Leo||Aug 23||lit. dwell in heat|
|Leo||Sep 8||condensed moisture makes dew white|
|Virgo||Sep 23||lit. autumn division (or center)|
|Libra||Oct 23||appearance of frost and descent of temperature|
|225°||start of winter||立冬
|Sagittarius||Dec 22||lit. winter extreme (of sun's height)|
- Simplified Chinese characters are shown in parentheses if they differ from the Traditional Chinese characters.
- Hanja is indicated in parentheses.
- Date can vary within a ±1 day range.
The "Song of Solar Terms" (Chinese: 節氣歌; pinyin: jiéqìgē) is used to ease the memorization of jiéqì:
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
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
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.