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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 proj ...
, 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 f ...
, the September
equinox A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" and se ...
may occur anytime from September 21 to 24. At the equinox, the Sun as viewed from the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
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, galaxi ...
summer and the beginning of astronomical autumn (autumnal equinox) in the
Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
, 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 f ...
. 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 proj ...
southwards is called the First Point of
Libra Libra generally refers to: * Libra (constellation), a constellation * Libra (astrology), an astrological sign based on the star constellation Libra may also refer to: Arts and entertainment * ''Libra'' (novel), a 1988 novel by Don DeLillo Musi ...
. 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 particu ...
, this point is no longer in the
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...
Libra Libra generally refers to: * Libra (constellation), a constellation * Libra (astrology), an astrological sign based on the star constellation Libra may also refer to: Arts and entertainment * ''Libra'' (novel), a 1988 novel by Don DeLillo Musi ...
, but rather in
Virgo Virgo may refer to: *Virgo (astrology), the sixth astrological sign of the zodiac * Virgo (constellation), a constellation *Virgo Cluster, a cluster of galaxies in the constellation Virgo *Virgo Stellar Stream, remains of a dwarf galaxy * Virgo Su ...
. 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 In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomeno ...
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 South is one of the cardinal directions or Points of the compass, compass points. The direction is the opposite of north and is perpendicular to both east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Pro ...
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 The Iranian calendars or Iranian chronology ( fa, گاه‌شماری ایرانی, ) are a succession of calendars invented or used for over two millennia in Iran, also known as Persia. One of the longest chronological records in human history, ...
. It is one of the
Iranian festivals The following is a list of festivals in Iran. Iranian festivals * Noruz: ''no'' means new and the word ''ruz'' means day, so ''Nowruz'' means starting a new day and it is the Celebration of the start of spring (Rejuvenation). It starts on th ...
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 Zoroastrianism is an Iranian religions, Iranian religion and one of the world's History of religion, oldest organized faiths, based on the teachings of the Iranian peoples, Iranian-speaking prophet Zoroaster. It has a Dualism in cosmology, du ...
.


East Asia

* In Japan is a public holiday.
Higan is a Buddhist holiday exclusively celebrated by Japanese sects for seven days; three days before and after both the Spring equinox ( shunbun) and Autumnal equinox ( shūbun). It is observed by nearly every Buddhist school in Japan. The tra ...
(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 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 Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
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 lunisolar ...
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 Written Chinese, 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 k ...
分 means ''"(equal) division"'' (within a season).


Judaism

* The Jewish
Sukkot or ("Booths, Tabernacles") , observedby = Jews, Samaritans, a few Protestant denominations, Messianic Jews, Semitic Neopagans , type = Jewish, Samaritan , begins = 15th day of Tishrei , ends = 21st day of Tishre ...
usually falls on the first
full moon The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon (when the ecliptic coordinate system, ecliptic longitudes of the Sun and Moon opp ...
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 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 In the history of France, the First Republic (french: Première République), sometimes referred to in historiography as Revolutionary France, and officially the French Republic (french: République française), was founded on 21 September 1792 ...
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 firs ...
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 A harvest festival is an annual celebration that occurs around the time of the main harvest of a given region. Given the differences in climate and crops around the world, harvest festivals can be found at various times at different places. ...
in the United Kingdom was celebrated on the Sunday of the full moon closest to the September equinox.


Neopaganism

* Neopagans observe the September equinox as a cardinal point on the
Wheel of the Year The Wheel of the Year is an annual cycle of seasonal festivals, observed by many modern pagans, consisting of the year's chief solar events (solstices and equinoxes) and the midpoints between them. While names for each festival vary among dive ...
. In the Northern Hemisphere some varieties of paganism adapt
Autumn Equinox Autumnal equinox or variations, may refer to: * September equinox, the autumnal equinox in the Northern Hemisphere * March equinox, the autumnal equinox in the Southern Hemisphere Other uses * Autumnal Equinox Day (Japanese: 秋分の日, ''Shūbu ...
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 In archaeology, timber circles are rings of upright wooden posts, built mainly by ancient peoples in the British Isles and North America. They survive only as gapped rings of post-holes, with no evidence they formed walls, making them distinct fr ...
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- ...
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 an ...
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 ve ...
*
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


References

{{Portal bar, Astronomy, Holidays, Stars, Spaceflight, Outer space, Solar System, Science Spherical astronomy Dynamics of the Solar System Astronomical events of the Solar System
Equinox A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" and se ...