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{{Location map-line|lat=0|caption=Equator in the [[world map|map of the Earth]]}} |
{{Location map-line|lat=0|caption=Equator in the [[world map|map of the Earth]]}} |
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[[File:Equator and Prime Meridian.svg|thumb|upright=1.35|Nations or territories that touch the Equator (red) or the [[IERS Reference Meridian]] (blue)]] |
[[File:Equator and Prime Meridian.svg|thumb|upright=1.35|Nations or territories that touch the Equator (red) or the [[IERS Reference Meridian]] (blue)]] |
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An '''equator''' of a rotating [[spheroid]] (such as a [[planet]]) is its zeroth [[circle of latitude]] (parallel). It is the imaginary line on the spheroid's surface, equidistant from its [[geographical pole|poles]], dividing it into [[northern hemisphere|northern]] and [[southern hemisphere]]s. In other words, it is the intersection of the spheroid's surface with the [[plane (mathematics)|plane]] [[perpendicular]] to its axis of [[rotation]] and midway between its [[geographical pole]]s. |
An '''equator''' of a rotating [[spheroid]] (such as a [[planet]]) is its zeroth [[circle of latitude]] (parallel). It is the [[imaginary line]] on the spheroid's surface, equidistant from its [[geographical pole|poles]], dividing it into [[northern hemisphere|northern]] and [[southern hemisphere]]s. In other words, it is the intersection of the spheroid's surface with the [[plane (mathematics)|plane]] [[perpendicular]] to its axis of [[rotation]] and midway between its [[geographical pole]]s. |
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On [[Earth]], ''the Equator'' is about {{cvt|40,075|km|mi}} long, of which 78.8% lies across water and 21.3% over land. [[Indonesia]] is the country straddling the greatest length of the equatorial line across both land and sea. |
On [[Earth]], ''the Equator'' is about {{cvt|40,075|km|mi}} long, of which 78.8% lies across water and 21.3% over land. [[Indonesia]] is the country straddling the greatest length of the equatorial line across both land and sea. |
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==Overview== |
==Overview== |
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{{Double image|right|Equator monument.jpg|150|Equator sign kenya.jpg|125|Top: A monument marking the Equator near the |
{{Double image|right|Equator monument.jpg|150|Equator sign kenya.jpg|125|''Top'': A monument marking the Equator near the city of [[Pontianak, Indonesia]]<br />''Bottom'': Road sign marking the Equator near [[Nanyuki]], [[Kenya]]}} |
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The [[latitude]] of the Earth's equator is, by definition, 0° (zero [[degree (angle)|degrees]]) of arc. The Equator is one of the five notable [[circle of latitude|circles of latitude]] on Earth; the other four are both [[polar circle]]s (the [[Arctic Circle]] and the [[Antarctic Circle]]) and both [[tropics|tropical circles]] (the [[Tropic of Cancer]] and the [[Tropic of Capricorn]]). The Equator is the only line of latitude which is also a [[great circle]] — that is, one whose plane passes through the center of the globe. The plane of Earth's equator, when projected outwards to the [[celestial sphere]], defines the [[celestial equator]]. |
The [[latitude]] of the Earth's equator is, by definition, 0° (zero [[degree (angle)|degrees]]) of arc. The Equator is one of the five notable [[circle of latitude|circles of latitude]] on Earth; the other four are both [[polar circle]]s (the [[Arctic Circle]] and the [[Antarctic Circle]]) and both [[tropics|tropical circles]] (the [[Tropic of Cancer]] and the [[Tropic of Capricorn]]). The Equator is the only line of latitude which is also a [[great circle]] — that is, one whose [[Plane (mathematics)|plane]] passes through the center of the globe. The plane of Earth's equator, when projected outwards to the [[celestial sphere]], defines the [[celestial equator]]. |
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In the cycle of Earth's [[season]]s, the equatorial plane runs through the Sun twice per [[year]]: on the [[equinox]]es in [[March equinox|March]] and [[September equinox|September]]. To a person on Earth, the Sun [[subsolar point|appears to travel above]] the Equator (or along the celestial equator) at these times. Light rays from the Sun's center are [[perpendicular]] to Earth's surface at the point of [[Noon#Solar noon|solar noon]] on the Equator. |
In the cycle of Earth's [[season]]s, the equatorial plane runs through the Sun twice per [[year]]: on the [[equinox]]es in [[March equinox|March]] and [[September equinox|September]]. To a person on Earth, the Sun [[subsolar point|appears to travel above]] the Equator (or along the celestial equator) at these times. Light rays from the Sun's center are [[perpendicular]] to Earth's surface at the point of [[Noon#Solar noon|solar noon]] on the Equator. |
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[[File:Equator Sao Tome.jpg|thumb|left|The Equator marked as it crosses [[Ilhéu das Rolas]], in São Tomé and Príncipe]] |
[[File:Equator Sao Tome.jpg|thumb|left|The Equator marked as it crosses [[Ilhéu das Rolas]], in [[São Tomé and Príncipe]]]] |
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[[File:equator Line Monument, Macapá city, Brazil.jpg|left|thumb|The Marco Zero monument marking the Equator in [[Macapá]], [[Brazil]].]] |
[[File:equator Line Monument, Macapá city, Brazil.jpg|left|thumb|The [[Marco Zero (São Paulo)|Marco Zero]] monument marking the Equator in [[Macapá]], [[Brazil]].]] |
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Locations on the Equator experience the shortest [[sunrise]]s and [[sunset]]s because the Sun's [[sun path|daily path]] is nearly perpendicular to the [[horizon]] for most of the year. The length of [[daylight]] (sunrise to sunset) is almost constant throughout the year; it is about 14 minutes longer than nighttime due to [[atmospheric refraction]] and the fact that sunrise begins (or sunset ends) as the upper limb, not the center, of the Sun's disk contacts the horizon. |
Locations on the Equator experience the shortest [[sunrise]]s and [[sunset]]s because the Sun's [[sun path|daily path]] is nearly perpendicular to the [[horizon]] for most of the year. The length of [[daylight]] (sunrise to sunset) is almost constant throughout the year; it is about 14 minutes longer than nighttime due to [[atmospheric refraction]] and the fact that sunrise begins (or sunset ends) as the upper limb, not the center, of the Sun's disk contacts the horizon. |
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Earth [[equatorial bulge|bulges slightly]] at the Equator; the "average" diameter of Earth is {{cvt|12750|km|mi}}, but the diameter at the Equator is about {{cvt|43|km|mi}} greater than at the poles.<ref name="National">{{cite web |url=http://education.nationalgeographic.com/education/encyclopedia/equator/?ar_a=1|title=Equator|author= |date= |work= |website=National Geographic - Education|accessdate=29 May 2013}}</ref> |
Earth [[equatorial bulge|bulges slightly]] at the Equator; the "average" diameter of Earth is {{cvt|12750|km|mi}}, but the diameter at the Equator is about {{cvt|43|km|mi}} greater than at the poles.<ref name="National">{{cite web |url=http://education.nationalgeographic.com/education/encyclopedia/equator/?ar_a=1|title=Equator|author= |date= |work= |website=National Geographic - Education|accessdate=29 May 2013}}</ref> |
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Sites near the Equator, such as the [[Guiana Space Centre]] in [[Kourou]], [[French Guiana]], are good locations for [[spaceport]]s as they have a faster rotational speed than other latitudes; the added velocity reduces the fuel needed to launch spacecraft. Since Earth [[retrograde and prograde motion|rotates eastward]], spacecraft must also be launched eastward (if not, to the southeast or northeast) to take advantage of this Earth-boost of speed.{{citation needed|date=April 2017}} |
Sites near the Equator, such as the [[Guiana Space Centre]] in [[Kourou]], [[French Guiana]], are good locations for [[spaceport]]s as they have a faster [[rotational speed]] than other latitudes; the added [[velocity]] reduces the fuel needed to launch spacecraft. Since Earth [[retrograde and prograde motion|rotates eastward]], spacecraft must also be launched eastward (if not, to the southeast or northeast) to take advantage of this Earth-boost of speed.{{citation needed|date=April 2017}} |
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== Geodesy == |
== Geodesy == |
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===Precise location=== |
===Precise location=== |
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The precise location of the Equator is not truly fixed; the true equatorial plane is perpendicular to the Earth's spin axis, which [[polar motion|drifts]] about {{convert|9|m|0}} during a year. This effect must be accounted for in detailed [[geophysical]] measurements.{{citation needed|date=April 2017}} |
The precise location of the Equator is not truly fixed; the true equatorial plane is perpendicular to the [[Axial tilt|Earth's spin axis]], which [[polar motion|drifts]] about {{convert|9|m|0}} during a year. This effect must be accounted for in detailed [[geophysical]] measurements.{{citation needed|date=April 2017}} |
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=== Exact length === |
=== Exact length === |
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In two widely used [[geodesy|geodetic]] standards, the Equator is modelled as a circle whose radius is a [[integer|whole number]] of metres. In 1976 the [[International Astronomical Union |
In two widely used [[geodesy|geodetic]] standards, the Equator is modelled as a circle whose [[radius]] is a [[integer|whole number]] of metres. In 1976, the [[International Astronomical Union]] (IAU) chose a radius of {{convert|6378.140|km}} (codified as the [[IAU (1976) System of Astronomical Constants|IAU-1976]] value), later refined by the [[International Union of Geodesy and Geophysics]] (IUGG) to {{convert|6378.137|km}} and adopted in [[World Geodetic System|WGS-84]]. Despite this change, the yet more recent IAU-2000 retained the old IAU-1976 value. If it were really circular, the length of the Equator would be exactly 2{{pi}} times the radius, namely {{convert|40075.036|km}}. However, due to the effect of the [[Earth tide|tides on the Earth's surface]] the actual circumference at the equator is about {{convert|40075.16|km}}. |
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The [[geographical mile]] is defined as one arc |
The [[geographical mile]] is defined as one [[arc-minute]] of the Equator, so it has different values depending on which radius is assumed. For example, by WSG-84, the distance is {{convert|1855.3248|m}}, while by IAU-2000, it is {{convert|1855.3257|m}}. This is a difference of less than {{Convert|1|mm||spell=in}} over the total distance (approximately {{convert|1.86|km||disp=or}}). |
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The earth is commonly modeled as a sphere flattened 0.336% along its axis. |
The earth is commonly modeled as a [[sphere]] flattened 0.336% along its axis. This makes the Equator 0.16% longer than a [[Meridian (geography)|meridian]] (a great circle passing through the two poles). The IUGG standard meridian is, to the nearest millimetre, {{convert|40007.862917|km}}, one arc-minute of which is {{convert|1852.216|m}}, explaining the [[International System of Units|SI]] standardization of the [[nautical mile]] as {{convert|1852|m}}, more than {{convert|3|m}} less than the [[geographical mile]]. |
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The sea-level surface of the Earth (the [[geoid]]) is irregular, so the actual length of the Equator is not so easy to determine. ''Aviation Week and Space Technology'' on 9 October 1961 reported that measurements using the Transit IV-A satellite had shown the equatorial "diameter" from longitude 11° West to 169° East to be {{convert|1000|ft}} greater than its "diameter" ninety degrees away.{{citation needed|date=March 2012}} |
The [[Sea level|sea-level]] surface of the Earth (the [[geoid]]) is irregular, so the actual length of the Equator is not so easy to determine. ''[[Aviation week and space technology|Aviation Week and Space Technology]]'' on 9 October 1961 reported that measurements using the [[Transit (satellite)|Transit]] IV-A satellite had shown the equatorial "diameter" from longitude 11° West to 169° East to be {{convert|1000|ft}} greater than its "diameter" ninety degrees away.{{citation needed|date=March 2012}} |
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⚫ | Certain navies, such as the [[Royal Navy]], [[Russian Navy]], and [[US Navy]], have a tradition of holding ceremonies aboard ships to mark sailors' first crossing of the Equator. These ceremonial events have in the past been notorious for their brutality.{{citation needed|date=April 2017}} Milder line-crossing ceremonies, typically featuring [[Neptune (god)|King Neptune]], are also held for passengers' entertainment on some civilian ocean liners and cruise ships.{{citation needed|date=January 2015}} |
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== Equatorial countries and territories == |
== Equatorial countries and territories == |
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{{kml}} |
{{kml}} |
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[[File:ECSundialGPS.jpg|thumb|upright|GPS reading taken on the Equator close to the [[Quitsato Sundial]], at [[Ciudad Mitad del Mundo|Mitad del Mundo]], [[Ecuador]].<ref name="Informe que determina la posición de la Línea Ecuatorial">{{cite web|author=Instituto Geográfico Militar de Ecuador|title=Memoria Técnica de la Determinación de la Latitud Cero|url=https://www.scribd.com/doc/97475201/Documento-Posicionamiento-Reloj-Solar|date=24 January 2005|language=Spanish}}</ref>]] |
[[File:ECSundialGPS.jpg|thumb|upright|[[Global Positioning System|GPS]] reading taken on the Equator close to the [[Quitsato Sundial]], at [[Ciudad Mitad del Mundo|Mitad del Mundo]], [[Ecuador]].<ref name="Informe que determina la posición de la Línea Ecuatorial">{{cite web|author=Instituto Geográfico Militar de Ecuador|title=Memoria Técnica de la Determinación de la Latitud Cero|url=https://www.scribd.com/doc/97475201/Documento-Posicionamiento-Reloj-Solar|date=24 January 2005|language=Spanish}}</ref>]] |
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The Equator passes through the land of 11 [[country|countries]]. Starting at the [[Prime Meridian]] and heading eastwards, the Equator passes through: |
The Equator passes through the land of 11 [[country|countries]]. Starting at the [[Prime Meridian]] and heading eastwards, the Equator passes through: |
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{| class="wikitable plainrowheaders" |
{| class="wikitable plainrowheaders" |
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! scope="row" | {{SOM}} |
! scope="row" | {{SOM}} |
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| Passing south of [[Jamame]] |
| Passing south of [[Jamame]] |
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|- |
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|-valign="top" |
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| style="background:#b0e0e6;" | {{Coord|0|0|N|42|53|E|type:waterbody|name=Indian Ocean}} |
| style="background:#b0e0e6;" | {{Coord|0|0|N|42|53|E|type:waterbody|name=Indian Ocean}} |
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! scope="row" style="background:#b0e0e6;" | [[Indian Ocean]] |
! scope="row" style="background:#b0e0e6;" | [[Indian Ocean]] |
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| {{Coord|0|0|N|127|24|E|type:country|name=Indonesia}} |
| {{Coord|0|0|N|127|24|E|type:country|name=Indonesia}} |
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! scope="row" | {{IDN}} |
! scope="row" | {{IDN}} |
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| |
|[[Kayoa]] and [[Halmahera]] islands |
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|- |
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| style="background:#b0e0e6;" | {{Coord|0|0|N|127|53|E|type:waterbody|name=Halmahera Sea}} |
| style="background:#b0e0e6;" | {{Coord|0|0|N|127|53|E|type:waterbody|name=Halmahera Sea}} |
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| {{Coord|0|0|N|80|6|W|type:country|name=Ecuador}} |
| {{Coord|0|0|N|80|6|W|type:country|name=Ecuador}} |
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! scope="row" | {{ECU}} |
! scope="row" | {{ECU}} |
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| Passing {{convert|24|km|abbr=on}} north of central [[Quito]], near [[Ciudad Mitad del Mundo|Mitad del Mundo]], and precisely at the location of [[Catequilla]], a pre-Columbian ruin |
| Passing {{convert|24|km|abbr=on}} north of central [[Quito]], near [[Ciudad Mitad del Mundo|Mitad del Mundo]], and precisely at the location of [[Catequilla]], a [[Pre-Columbian era|pre-Columbian]] ruin. Also, [[Isabela Island (Ecuador)|Isabela Island]] in the [[Galápagos Islands]] |
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|- |
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| {{Coord|0|0|N|75|32|W|type:country|name=Colombia}} |
| {{Coord|0|0|N|75|32|W|type:country|name=Colombia}} |
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| {{Coord|0|0|N|70|3|W|type:country|name=Brazil}} |
| {{Coord|0|0|N|70|3|W|type:country|name=Brazil}} |
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! scope="row" | {{BRA}} |
! scope="row" | {{BRA}} |
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| [[Amazonas (Brazilian state)|Amazonas]] |
| [[Amazonas (Brazilian state)|Amazonas]], [[Roraima]], [[Pará]], [[Amapá]] (passing slightly south of the city center of the state capital [[Macapá]], and precisely at the [[Marco Zero (São Paulo)|Marco Zero]] monument and the Avenue Equatorial) |
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|- |
|- |
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| style="background:#b0e0e6;" | {{Coord|0|0|N|49|21|W|type:waterbody|name=Atlantic Ocean}} |
| style="background:#b0e0e6;" | {{Coord|0|0|N|49|21|W|type:waterbody|name=Atlantic Ocean}} |
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! scope="row" style="background:#b0e0e6;" | [[Atlantic Ocean]] |
! scope="row" style="background:#b0e0e6;" | [[Atlantic Ocean]] |
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| style="background:#b0e0e6;" | At the [[:sv:Canal Perigoso| |
| style="background:#b0e0e6;" | At the Perigoso Canal ([[:sv:Canal Perigoso|''<small>sv</small>'']]) on the mouth of the [[Amazon River]] |
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|date=March 2011}} |
|date=March 2011}} |
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</div> |
</div> |
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⚫ | Certain navies, such as the [[Royal Navy]], [[Russian Navy]], and [[US Navy]], have a tradition of holding ceremonies aboard ships to mark sailors' first crossing of the Equator. These ceremonial events have in the past been notorious for their brutality.{{citation needed|date=April 2017}} Milder line-crossing ceremonies, typically featuring [[Neptune (god)|King Neptune]], are also held for passengers' entertainment on some civilian ocean liners and cruise ships.{{citation needed|date=January 2015}} |
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== See also == |
== See also == |