Solar term

File:24solarterms.png

The 24 solar terms with labels in Japanese

Template:Solar terms A solar term (or jiéqì, Template:Lang-zh) is any of twenty-four periods in traditional Chinese 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; 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 (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 Template:Ill (). 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.

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 Template:Ill (Template:Lang-zh), so there are 72 pentads in a year, consisting of five, rarely six, days. Most of them are 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. 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.

Numbering

The solar terms used to mark the midpoint of the month (marked with "Z", for Template:Lang-zh) are considered the major terms, while the solar terms used to mark the start of the month (marked with "J", for Template:Lang-zh) are deemed minor. The year starts with Lichun (J1) and ends with Dahan (Z12).

Multilingual list

Season	Chinese zodiac & Earthly Branch of Month	Sun's ecliptic longitude	Chinese name	Korean name	Vietnamese name	Japanese name	Ryukyuan (Okinawan) name	English name (Hong Kong Observatory)	English name	Gregorian Date (± 1 day)	Reference for Month Intercalating	Corresponding Western astrological sign
Spring	Tiger () Template:Transliteration ()	315°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Spring commences	Beginning of Spring	Feb 4	1st month initial	Aquarius
		330°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Rain water	Rain Water	Feb 19	1st month midpoint	Pisces
	Rabbit () Template:Transliteration ()	345°	() Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration; Template:Transliteration; Template:Transliteration	Insects waken	Awakening of Insects	Mar 6	2nd month initial
		0°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Vernal equinox	Spring Equinox	Mar 21	2nd month midpoint	Aries
	Dragon () Template:Transliteration ()	15°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Bright and clear	Pure Brightness	Apr 5	3rd month initial
		30°	() Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Corn rain	Grain Rain	Apr 20	3rd month midpoint	Taurus
Summer	Snake () Template:Transliteration ()	45°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Summer commences	Beginning of Summer	May 6	4th month initial
		60°	() Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Corn forms	Grain Buds	May 21	4th month midpoint	Gemini
	Horse () Template:Transliteration ()	75°	() Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Corn on ear	Grain in Ear	Jun 6	5th month initial
		90°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Summer solstice	Summer Solstice	Jun 21	5th month midpoint	Cancer
	Goat () Template:Transliteration ()	105°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Moderate heat	Minor Heat	Jul 7	6th month initial
		120°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Great heat	Major heat	Jul 23	6th month midpoint	Leo
Autumn	Monkey () Template:Transliteration ()	135°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Autumn commences	Beginning of Autumn	Aug 8	7th month initial
		150°	() Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	End of heat	End of Heat	Aug 23	7th month midpoint	Virgo
	Rooster () Template:Transliteration ()	165°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	White dew	White Dew	Sep 8	8th month initial
		180°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Autumnal equinox	Autumn Equinox	Sep 23	8th month midpoint	Libra
	Dog () Template:Transliteration ()	195°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Cold dew	Cold Dew	Oct 8	9th month initial
		210°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Frost	Frost's Descent	Oct 23	9th month midpoint	Scorpio
Winter	Pig () Template:Transliteration ()	225°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Winter commences	Beginning of Winter	Nov 7	10th month initial
		240°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Light snow	Minor Snow	Nov 22	10th month midpoint	Sagittarius
	Rat () Template:Transliteration ()	255°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Heavy snow	Major Snow	Dec 7	11th month initial
		270°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Winter solstice	Winter Solstice	Dec 22	11th month midpoint	Capricorn
	Ox () Template:Transliteration ()	285°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Moderate cold	Minor Cold	Jan 6	12th month initial
		300°	Template:Transliteration	Template:Transliteration	Template:Vi-nom	Template:Transliteration	Template:Transliteration	Severe cold	Major Cold	Jan 20	12th month midpoint	Aquarius

Chinese mnemonic song

The "Song of Solar Terms" (Template:Lang-zh) is used to ease the memorization of jieqi:

Traditional Chinese

Simplified Chinese

Pinyin

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

File:Tiết Khí.svg

Chart with the solar terms and their Vietnamese names

The modern definition using ecliptic longitudes, introduced by the Shixian calendar, is known as (Template:Transliteration, Template:Gloss). 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. The JPL Horizons On-Line Ephemeris System may be used to query for exact times of solar terms.

The older method is known as (Template:Transliteration, Template:Gloss) and simply divides the tropical year into 24 equal parts.

Regional note

In Japan, the term Template:Transliteration () originally referred to the eves of Template:Transliteration (, 315°, the beginning of Spring), Template:Transliteration (, 45°, the beginning of Summer), Template:Transliteration (, 135°, the beginning of Autumn), and Template:Transliteration (, 225°, the beginning of Winter), but currently mostly refers to the day before Template:Transliteration. 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

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