The September equinox (or southward equinox) is the moment when the
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
appears to cross the
celestial equator
The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. This plane of reference bases the equatorial coordinate system. In other words, the celestial equator is an abstract projecti ...
, heading southward. Because of differences between the
calendar
A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day within such a system. A calendar is also a physi ...
year and the
tropical year
A tropical year or solar year (or tropical period) is the time that the Sun takes to return to the same position in the sky of a celestial body of the Solar System such as the Earth, completing a full cycle of seasons; for example, the time fro ...
, the September
equinox may occur anytime from September 21 to 24.
At the equinox, the Sun as viewed from the
equator rises due east and
sets due west. Before the Southward equinox, the Sun rises and sets more northerly, and afterwards, it rises and sets more southerly.
The equinox may be taken to mark the end of
astronomical
Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galax ...
summer and the beginning of astronomical autumn (autumnal equinox) in the
Northern Hemisphere, while marking the end of astronomical winter and the start of astronomical spring (vernal equinox) in the
Southern Hemisphere.
Occurrences
The September equinox is one point in time commonly used to determine the length of the
tropical year
A tropical year or solar year (or tropical period) is the time that the Sun takes to return to the same position in the sky of a celestial body of the Solar System such as the Earth, completing a full cycle of seasons; for example, the time fro ...
.
The dates and times of the September equinoxes that occur from the year 2017 to 2027 (UTC) are listed as follows:
Constellation
The point where the Sun crosses the
celestial equator
The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. This plane of reference bases the equatorial coordinate system. In other words, the celestial equator is an abstract projecti ...
southwards is called the First Point of
Libra. However, because of the
precession of the equinoxes
In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In partic ...
, this point is no longer in the
constellation Libra, but rather in
Virgo.
The solar point of the September equinox passed from Libra and into Virgo in −729 (730 BCE) and will enter
Leo in 2439.
Apparent movement of the Sun in relation to the horizon
At the equinox, the Sun rises directly in the east and sets directly in the west. However, because of
refraction it will usually appear slightly above the horizon at the moment when its "true" middle is rising or setting. For viewers at
the north or
south poles, it moves virtually horizontally on or above the horizon, not obviously rising or setting apart from the movement in "declination" (and hence altitude) of a little under a half (0.39) degree per day.
For observers in either hemisphere not at the poles, the Sun rises and sets more and more to the south during the 3 months following the September equinox. This period is the second half of a 6-month long southerly movement, beginning with the
June solstice
The June solstice is the solstice on Earth that occurs annually between 20 and 22 June according to the Gregorian calendar. In the Northern Hemisphere, the June solstice is the summer solstice (the day with the longest period of daylight), whil ...
when the Sun rises and sets at its most northern point.
Culture
Calendars
The September equinox marked the first day of the
French Republican Calendar.
Commemorations
West Asia
* The Southward equinox marks the first day of Mehr or Libra in the
Iranian calendar. It is one of the
Iranian festivals called Jashne
Mihragan
Mehregan ( fa, ) or Jashn-e Mehr ( ''Mithra Festival'') is a Zoroastrian and Iranian festival celebrated to honor the yazata Mithra ( fa, Mehr), which is responsible for friendship, affection and love.
Name
"Mehregan" is derived from the Middl ...
, or the festival of sharing or love in
Zoroastrianism.
East Asia
* In Japan is a public holiday.
Higan (お彼岸) is a Buddhist holiday exclusively celebrated by Japanese sects during both the Spring and Autumnal Equinox.
* In Korea,
Chuseok
''Chuseok'' (; , literally "autumn evening"), also known as ''Hangawi'' (Hangul: ; ; from archaic Korean for "the great middle (of autumn)"), is a major mid-autumn harvest festival and a three-day holiday in South Korea celebrated on the 15th ...
is a major harvest festival and a three-day holiday celebrated around the Autumn Equinox.
* The
Mid-Autumn Festival
The Mid-Autumn Festival (Chinese: / ), also known as the Moon Festival or Mooncake Festival, is a traditional festival celebrated in Chinese culture. Similar holidays are celebrated in Japan (), Korea (), Vietnam (), and other countries in Eas ...
is celebrated on the 15th day of the 8th
lunar month
In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month.
Variations
In Shona, Middle Eastern, and Eur ...
, often near the autumnal equinox day, and is an official holiday in mainland China, Hong Kong,
Taiwan and in many countries with a significant Chinese minority. As the lunar calendar is not synchronous with the Gregorian calendar, this date could be anywhere from mid-September to early October.
* The traditional East Asian calendars divide a year into 24
solar term
A solar term 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 lunisola ...
s (节气, literally "climatic segments"), and the autumnal equinox (''
Qiūfēn'', ) marks the ''middle'' of the autumn season. In this context, the
Chinese character
Chinese characters () are logograms developed for the writing of Chinese. In addition, they have been adapted to write other East Asian languages, and remain a key component of the Japanese writing system where they are known as ''kanji' ...
分 means ''"(equal) division"'' (within a season).
Judaism
* The Jewish
Sukkot usually falls on the first
full moon after the northern hemisphere autumnal equinox, although occasionally (In the modern Jewish calendar, three times every 19 years) it will occur on the second full moon.
*
Rosh Hashanah
Rosh HaShanah ( he, רֹאשׁ הַשָּׁנָה, , literally "head of the year") is the Jewish New Year. The biblical name for this holiday is Yom Teruah (, , lit. "day of shouting/blasting") It is the first of the Jewish High Holy Days (, , " ...
falls on a
new moon close to this equinox.
Europe
*
Dożynki
Dożynki (''Dozhinki'', ua, Обжинки, Obzhynky, pl, Dożynki, russian: Обжинки, Obzhynki; be, Прачыстая, '' Prachystaya''; cs, Dožínky, Obžinky; csb, Òżniwinë; ''Dormition'') is a Slavic harvest festival. In pre-C ...
is a Slavic harvest festival. In pre-Christian times the feast usually fell on the autumn equinox.
* The Southward equinox was "New Year's Day" in the
French Republican Calendar, which was in use from 1793 to 1805. The
French First Republic was proclaimed and the
French monarchy
France was ruled by monarchs from the establishment of the Kingdom of West Francia in 843 until the end of the Second French Empire in 1870, with several interruptions.
Classical French historiography usually regards Clovis I () as the fir ...
was abolished on September 21, 1792, making the following day (the equinox day that year) the first day of the "Republican Era" in France. The start of every year was to be determined by astronomical calculations following the real Sun and not the mean Sun.
* The traditional
harvest festival in the United Kingdom was celebrated on the Sunday of the full moon closest to the September equinox.
Neopaganism
*
Neopagan
Modern paganism, also known as contemporary paganism and neopaganism, is a term for a religion or family of religions influenced by the various historical pre-Christian beliefs of pre-modern peoples in Europe and adjacent areas of North Afric ...
s observe the September equinox as a cardinal point on the
Wheel of the Year. In the Northern Hemisphere some varieties of paganism adapt
Autumn Equinox traditions. In the Southern Hemisphere, the vernal equinox corresponds with
Ostara.
Americas
*The reconstructed
Cahokia Woodhenge
The Cahokia Woodhenge was a series of large timber circles located roughly to the west of Monks Mound at the Mississippian culture Cahokia archaeological site near Collinsville, Illinois. They are thought to have been constructed between 900 and ...
, a large
timber circle located at the
Mississippian culture Cahokia
The Cahokia Mounds State Historic Site ( 11 MS 2) is the site of a pre-Columbian Native American city (which existed 1050–1350 CE) directly across the Mississippi River from modern St. Louis, Missouri. This historic park lies in south-w ...
archaeological site
An archaeological site is a place (or group of physical sites) in which evidence of past activity is preserved (either prehistoric or historic or contemporary), and which has been, or may be, investigated using the discipline of archaeology and ...
near
Collinsville, Illinois
Collinsville is a city located mainly in Madison County, and partially in St. Clair County, Illinois. As of the 2010 census, the city had a population of 25,579, an increase from 24,707 in 2000. Collinsville is approximately from St. Louis, Mi ...
,
is the site of annual equinox and solstice sunrise observances. An announcement for the 2017 observance said "Out of respect for Native American beliefs, no rituals or ceremonies will be held at the free event. But visitors will stand in the same place where the Mississippian people once gathered to watch the sun rise."
See also
*
March equinox
The March equinox or northward equinox is the equinox on the Earth when the subsolar point appears to leave the Southern Hemisphere and cross the celestial equator, heading northward as seen from Earth. The March equinox is known as the verna ...
*
June solstice
The June solstice is the solstice on Earth that occurs annually between 20 and 22 June according to the Gregorian calendar. In the Northern Hemisphere, the June solstice is the summer solstice (the day with the longest period of daylight), whil ...
*
December solstice
The December solstice, also known as the southern solstice, is the solstice that occurs each December – typically on 21 December, but may vary by one day in either direction according to the Gregorian calendar. In the Northern Hemisphere, the ...
References
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Dynamics of the Solar System
Astronomical events of the Solar System
Equinox