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{{Other uses}}
{{More footnotes|date=December 2010}}
{{pp-move-indef}}
{{Location map-line|lat=0}}
[[File:Equator and Prime Meridian.svg|thumb|300px|Nations or territories that touch the Equator (red) or the [[IERS Reference Meridian]] (blue)]]

An '''equator''' is the intersection of a [[sphere]]'s surface with the [[plane (mathematics)|plane]] perpendicular to the sphere's [[rotation|axis of rotation]] and midway between the poles. '''The Equator''' usually refers to the [[Earth]]'s equator: an imaginary line on the Earth's surface equidistant from the [[North Pole]] and [[South Pole]], dividing the Earth into the [[Northern Hemisphere]] and [[Southern Hemisphere]]. Other [[planet]]s and astronomical bodies have equators similarly defined. Earth's equator is about {{Convert|40,075|km}} long; 78.7% is across water and 21.3% is over land.

== Geodesy of the Earth's Equator ==
The [[latitude]] of the Earth's Equator is by definition 0° (zero [[degree (angle)|degree]]s). The Equator is one of the five notable [[circle of latitude|circles of latitude]] on Earth, with the others being the two [[Polar Circle]]s: the [[Arctic Circle]] and the [[Antarctic Circle]], and the two 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]]. The imaginary circle obtained when the Earth's equator is projected onto the sky is called the [[celestial equator]].
{{Double image|right|Equator monument.jpg|150|Equator sign kenya.jpg|125|Left: A monument marking the Equator near the town of [[Pontianak, Indonesia]]<br />Right: Road sign marking the Equator near [[Nanyuki]], Kenya}}

In its [[season]]al apparent movement across the sky the sun passes over the Equator twice each [[year]], at the March and September [[equinox]]es. At the moment of the equinox, light rays from the center of the [[Sun]] are [[perpendicular]] to the surface of the earth at the point on the Equator experiencing solar noon.

[[File:Equator Sao Tome.jpg|thumb|left|The Equator marked as it crosses [[Ilhéu das Rolas]], in São Tomé and Príncipe]]

Places on the Equator experience the quickest [[sunrise]]s and [[sunset]]s since the sun rises and sets almost vertically throughout the year. The length of a day (sunrise to sunset) at the Equator is almost constant during the year; each day is about 14 minutes longer than night because of [[atmospheric refraction]] and the fact that sunrise/sunset is the moment when the ''edge'' of the Sun's disk passes the [[horizon]], rather than its centre.

The Earth [[equatorial bulge|bulges slightly at the Equator]]. Its "average" diameter is {{convert|12750|km|0}}, but at the Equator the diameter is about {{convert|43|km|0}} 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= |publisher=National Geographic - Education|accessdate=29 May 2013}}</ref>

Locations near the Equator are good sites for [[spaceport]]s, such as the [[Guiana Space Centre]] in [[Kourou]], [[French Guiana]], as they are moving faster than other latitudes due to the Earth's rotation, and the added velocity reduces the fuel needed to launch spacecraft. Spacecraft must launch to the east, southeast, or northeast to take advantage of this.

===Precise location===
[[File:Equator Line Monument, Macapá city, Brazil.jpg|left|thumb|The Marco Zero monument marking the Equator in [[Macapá]], [[Brazil]].]]
The Equator, like the [[Tropics]], is not quite fixed. The true equatorial plane is always perpendicular to the Earth's spin axis; this axis is fairly stable but its [[polar motion|position drifts]] about {{convert|15|m|0}} during a year and the Equator shifts likewise.

== Equatorial seasons and climate ==
{{Main|Seasons|Tropics|Effect of sun angle on climate}}

[[Image:seasons.svg|frame|right|<br/>Diagram of the seasons, depicting the situation at the December solstice. Regardless of the time of day (i.e. the [[Earth]]'s rotation on its axis), the [[North Pole]] will be dark, and the [[South Pole]] will be illuminated; see also [[arctic winter]]. In addition to the density of [[Angle of incidence|incident]] light, the [[dissipation]] of light in the [[Earth's atmosphere|atmosphere]] is greater when it falls at a shallow angle.]]
Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution. During the year the northern and southern hemispheres are inclined toward or away from the sun according to Earth's position in its orbit. The hemisphere inclined toward the sun receives more sunlight and is in summer, while the other hemisphere receives less sun and is in winter (see [[solstice]]). At the [[equinox]] the Earth's axis is not tilted toward the sun and the day is about 12 hours long over most of the Earth.

Near the Equator there is little distinction between summer, winter, autumn, or spring. The temperatures are usually high year-round—with the exception of high mountains in [[South America]] and in [[Africa]]. (See [[Andes Mountains]] and [[Mt. Kilimanjaro]].) The temperature at the Equator can plummet during [[rainstorm]]s. In many tropical regions people identify two seasons: the wet season and the dry season, but many places close to the Equator are on the oceans or rainy throughout the year. The seasons can vary depending on elevation and proximity to an ocean.

The Equator lies mostly on the three largest [[ocean]]s: the [[Pacific Ocean]], the [[Atlantic Ocean]], and the [[Indian Ocean]]. The highest point on the Equator is at the elevation of {{convert|4690|m|0}}, at {{coord|0|0|0|N|77|59|31|W|type:landmark_region:EC|name=highest point on the Equator}}, found on the southern slopes of [[Volcán Cayambe]] [summit {{convert|5790|m|0}}] in [[Ecuador]]. This is slightly above the [[snow line]], and is the only place on the Equator where snow lies on the ground. At the Equator the snow line is around {{convert|1000|m|ft|-1}} ''lower'' than on [[Mount Everest]] and as much as {{convert|2000|m|ft|-1}} lower than the highest snow line in the world near the [[Tropic of Capricorn]] on [[Llullaillaco]].

== Equatorial countries and territories ==
{{kml}}
The Equator traverses the land and/or territorial waters of 14 [[country|countries]]. Starting at the [[Prime Meridian]] and heading eastwards, the Equator passes through:
{| class="wikitable plainrowheaders"
! scope="col" | Co-ordinates
! scope="col" | Country, territory or sea
! scope="col" | Notes
|-
| style="background:#b0e0e6;" | {{Coord|0|N|0|E|type:landmark|name=Prime Meridian}}
! scope="row" style="background:#b0e0e6;" | [[Atlantic Ocean]]
| style="background:#b0e0e6;" | [[Gulf of Guinea]]
|-
| {{Coord|0|0|N|6|31|E|type:country|name=São Tomé and Príncipe}}
! scope="row" | {{STP}}
| [[Ilhéu das Rolas]]
|-
| style="background:#b0e0e6;" | {{Coord|0|0|N|6|31|E|type:waterbody|name=Atlantic Ocean}}
! scope="row" style="background:#b0e0e6;" | [[Atlantic Ocean]]
| style="background:#b0e0e6;" | [[Gulf of Guinea]]
|-
| {{Coord|0|0|N|9|21|E|type:country|name=Gabon}}
! scope="row" | {{GAB}}
|
|-
| {{Coord|0|0|N|13|56|E|type:country|name=Republic of the Congo}}
! scope="row" | {{COG}}
| Passing through the town of [[Makoua]].
|-
| {{Coord|0|0|N|17|46|E|type:country|name=Democratic Republic of the Congo}}
! scope="row" | {{COD}}
| Passing 9&nbsp;km south of central [[Butembo]]
|-
| {{Coord|0|0|N|29|43|E|type:country|name=Uganda}}
! scope="row" | {{UGA}}
| Passing 32&nbsp;km south of central [[Kampala]]
|-
| style="background:#b0e0e6;" | {{Coord|0|0|N|32|22|E|type:waterbody|name=Lake Victoria}}
! scope="row" style="background:#b0e0e6;" | [[Lake Victoria]]
| style="background:#b0e0e6;" | Passing through some islands of {{UGA}}
|-
| {{Coord|0|0|N|34|0|E|type:country|name=Kenya}}
! scope="row" | {{KEN}}
| Passing 6&nbsp;km north of central [[Kisumu]]
|-
| {{Coord|0|0|N|41|0|E|type:country|name=Somalia}}
! scope="row" | {{SOM}}
|
|-valign="top"
| style="background:#b0e0e6;" | {{Coord|0|0|N|42|53|E|type:waterbody|name=Indian Ocean}}
! scope="row" style="background:#b0e0e6;" | [[Indian Ocean]]
| style="background:#b0e0e6;" | Passing between [[Huvadhu Atoll]] and [[Fuvahmulah]] of the {{MDV}}
|-
| {{Coord|0|0|N|98|12|E|type:country|name=Indonesia}}
! scope="row" | {{IDN}}
| The [[Batu Islands]], [[Sumatra]] and the [[Lingga Islands]]
|-
| style="background:#b0e0e6;" | {{Coord|0|0|N|104|34|E|type:waterbody|name=Karimata Strait}}
! scope="row" style="background:#b0e0e6;" | [[Karimata Strait]]
| style="background:#b0e0e6;" |
|-
| {{Coord|0|0|N|109|9|E|type:country|name=Indonesia}}
! scope="row" | {{IDN}}
| [[Borneo]]
|-
| style="background:#b0e0e6;" | {{Coord|0|0|N|117|30|E|type:waterbody|name=Makassar Strait}}
! scope="row" style="background:#b0e0e6;" | [[Makassar Strait]]
| style="background:#b0e0e6;" |
|-
| {{Coord|0|0|N|119|40|E|type:country|name=Indonesia}}
! scope="row" | {{IDN}}
| [[Sulawesi|Sulawesi (Celebes)]]
|-
| style="background:#b0e0e6;" | {{Coord|0|0|N|120|5|E|type:waterbody|name=Gulf of Tomini}}
! scope="row" style="background:#b0e0e6;" | [[Gulf of Tomini]]
| style="background:#b0e0e6;" |
|-
| style="background:#b0e0e6;" | {{Coord|0|0|N|124|0|E|type:waterbody|name=Molucca Sea}}
! scope="row" style="background:#b0e0e6;" | [[Molucca Sea]]
| style="background:#b0e0e6;" |
|-
| {{Coord|0|0|N|127|24|E|type:country|name=Indonesia}}
! scope="row" | {{IDN}}
| Kayoa and [[Halmahera]] islands
|-
| style="background:#b0e0e6;" | {{Coord|0|0|N|127|53|E|type:waterbody|name=Halmahera Sea}}
! scope="row" style="background:#b0e0e6;" | [[Halmahera Sea]]
| style="background:#b0e0e6;" |
|-
| {{Coord|0|0|N|129|20|E|type:country|name=Indonesia}}
! scope="row" | {{IDN}}
| Gebe Island
|-valign="top"
| style="background:#b0e0e6;" | {{Coord|0|0|N|129|21|E|type:waterbody|name=Pacific Ocean}}
! scope="row" style="background:#b0e0e6;" | [[Pacific Ocean]]
| style="background:#b0e0e6;" | Passing 570 m north of [[Waigeo]] island, {{IDN}}<br/> Passing 42&nbsp;km north of {{NRU}}<br/> Passing 13&nbsp;km south of [[Aranuka]] atoll, {{KIR}}<br/> Passing 21&nbsp;km south of [[Baker Island]], {{UMI}}<br/> Passing 40&nbsp;km north of [[Jarvis Island]], {{UMI}}
|-
| {{Coord|0|0|N|91|35|W|type:country|name=Ecuador}}
! scope="row" | {{ECU}}
| [[Isabela Island (Ecuador)|Isabela Island]] in the [[Galápagos Islands]]
|-
| style="background:#b0e0e6;" | {{Coord|0|0|N|91|13|W|type:waterbody|name=Pacific Ocean}}
! scope="row" style="background:#b0e0e6;" | [[Pacific Ocean]]
| style="background:#b0e0e6;" |
|-
| {{Coord|0|0|N|80|6|W|type:country|name=Ecuador}}
! scope="row" | {{ECU}}
| Passing 24&nbsp;km north of central [[Quito]], near [[Ciudad Mitad del Mundo|Mitad del Mundo]]
|-
| {{Coord|0|0|N|75|32|W|type:country|name=Colombia}}
! scope="row" | {{COL}}
| Passing 4.3&nbsp;km north of the border with [[Peru]]
|-valign="top"
| {{Coord|0|0|N|70|3|W|type:country|name=Brazil}}
! scope="row" | {{BRA}}
| [[Amazonas (Brazilian state)|Amazonas]]<br/> [[Roraima]]<br/> Amazonas<br/> [[Pará]]<br/> [[Amapá]]<br/> Pará - islands in the mouth of the [[Amazon River]]
|-
| style="background:#b0e0e6;" | {{Coord|0|0|N|49|20|W|type:waterbody|name=Atlantic Ocean}}
! scope="row" style="background:#b0e0e6;" | [[Atlantic Ocean]]
| style="background:#b0e0e6;" |
|-
|}

Despite its name, no part of [[Equatorial Guinea]]'s territory lies on the Equator. However, its island of [[Annobón Province|Annobón]] is {{convert|155|km}} south of the Equator, and the rest of the country lies to the north.

[[File:ECSundialGPS.jpg|thumb|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=http://www.scribd.com/doc/97475201/Documento-Posicionamiento-Reloj-Solar|date=24 January 2005|language=Español}}</ref>]]

== Crossing the Equator ==
{{Main|Line-crossing ceremony}}

Certain navies, such as the [[Royal Navy]] and the [[US Navy]], have a tradition of holding ceremonies on board ship to mark sailors' first crossing of the Equator. These rites of initiation have in the past been notorious for their brutality. Milder line-crossing ceremonies, typically featuring [[Neptune (god)|King Neptune]], are also held for passengers' entertainment on some civilian ocean liners and cruise ships.

== Exact length ==
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}}, later refined by the [[International Union of Geodesy and Geophysics|IUGG]] to {{convert|6378.137|km}} and adopted in [[World Geodetic System|WGS-84]], though the yet more recent IAU-2000 has retained the old IAU-1976 value. If it were really circular the length of the Equator would be exactly 2π times the assumed radius.

The [[geographical mile]] is defined as one arc minute of the Equator, so it has different values depending on which radius is assumed, e.g. {{convert|1855.3248|m}} for WGS84 or {{convert|1855.3257|m}} for IAU-2000.

The earth is modelled commonly 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]].

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}}

== Climate ==
Lowlands around the Equator generally have a [[tropical rainforest climate]], also known as an equatorial climate, though cold currents cause some regions to have [[tropical monsoon climate]]s with a [[dry season]] in the middle of the year. Usually, average annual temperature is around {{convert|30|°C|°F|abbr=on}} during the day and {{convert|23|°C|°F|abbr=on}} at night. Rainfall is very high, usually from {{convert|2500|to|3500|mm|abbr=on}} per year. Average rainy days are around 200 per year and average annual sunshine hours around 2,000.
{{Weather box|location = [[Macapá]], [[Brazil]] in South America
|metric first = yes
|single line = yes
|temperature colour=pastel
|temperature colour=pastel
|Jan high C = 29.7
|Jan high C = 29.7

Revision as of 18:59, 17 September 2014

ummm |temperature colour=pastel |Jan high C = 29.7 |Feb high C = 29.2 |Mar high C = 29.3 |Apr high C = 29.5 |May high C = 30.0 |Jun high C = 30.3 |Jul high C = 30.6 |Aug high C = 31.5 |Sep high C = 32.1 |Oct high C = 32.6 |Nov high C = 32.3 |Dec high C = 31.4 |year high C = 30.71 |Jan mean C = 26.4 |Feb mean C = 26.2 |Mar mean C = 26.3 |Apr mean C = 26.5 |May mean C = 26.8 |Jun mean C = 26.8 |Jul mean C = 26.8 |Aug mean C = 27.4 |Sep mean C = 27.8 |Oct mean C = 28.1 |Nov mean C = 27.9 |Dec mean C = 27.4 |year mean C = 27.03 |Jan low C = 23.0 |Feb low C = 23.1 |Mar low C = 23.2 |Apr low C = 23.5 |May low C = 23.5 |Jun low C = 23.2 |Jul low C = 22.9 |Aug low C = 23.3 |Sep low C = 23.4 |Oct low C = 23.5 |Nov low C = 23.5 |Dec low C = 23.4 |year low C = 23.29 |rain colour=green |Jan rain mm = 299.6 |Feb rain mm = 347.0 |Mar rain mm = 407.2 |Apr rain mm = 384.3 |May rain mm = 351.5 |Jun rain mm = 220.1 |Jul rain mm = 184.8 |Aug rain mm = 98.00 |Sep rain mm = 42.60 |Oct rain mm = 35.50 |Nov rain mm = 58.40 |Dec rain mm = 142.5 |Jan rain days = 23 |Feb rain days = 22 |Mar rain days = 24 |Apr rain days = 24 |May rain days = 25 |Jun rain days = 22 |Jul rain days = 19 |Aug rain days = 13 |Sep rain days = 6 |Oct rain days = 5 |Nov rain days = 6 |Dec rain days = 14 |unit rain days = 0.1 mm |Jan sun = 148.8 |Feb sun = 113.1 |Mar sun = 108.5 |Apr sun = 114.0 |May sun = 151.9 |Jun sun = 189.0 |Jul sun = 226.3 |Aug sun = 272.8 |Sep sun = 273.0 |Oct sun = 282.1 |Nov sun = 252.0 |Dec sun = 204.6 |year sun = 2336.1 |source 1 = World Meteorological Organization (UN),[1] Hong Kong Observatory[2] |date=March 2011}}

Climate data for Pontianak, Indonesia in Asia
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Mean daily maximum °C (°F) 32.4
(90.3) 		32.7
(90.9) 		32.9
(91.2) 		33.2
(91.8) 		33.0
(91.4) 		33.2
(91.8) 		32.9
(91.2) 		33.4
(92.1) 		32.6
(90.7) 		32.6
(90.7) 		32.2
(90.0) 		32.0
(89.6) 		32.7
(90.9)
Daily mean °C (°F) 27.6
(81.7) 		27.7
(81.9) 		28.0
(82.4) 		28.2
(82.8) 		28.2
(82.8) 		28.2
(82.8) 		27.7
(81.9) 		27.9
(82.2) 		27.6
(81.7) 		27.7
(81.9) 		27.4
(81.3) 		27.2
(81.0) 		27.7
(81.9)
Mean daily minimum °C (°F) 22.7
(72.9) 		22.6
(72.7) 		23.0
(73.4) 		23.2
(73.8) 		23.4
(74.1) 		23.1
(73.6) 		22.5
(72.5) 		22.3
(72.1) 		22.6
(72.7) 		22.8
(73.0) 		22.6
(72.7) 		22.4
(72.3) 		22.7
(72.9)
Average rainfall mm (inches) 260
(10.2) 		215
(8.5) 		254
(10.0) 		292
(11.5) 		256
(10.1) 		212
(8.3) 		201
(7.9) 		180
(7.1) 		295
(11.6) 		329
(13.0) 		400
(15.7) 		302
(11.9) 		3,196
(125.8)
Average rainy days (≥ 0.1 mm) 15 13 21 22 20 18 16 25 14 27 25 22 238
Source: World Meteorological Organization (UN)[3]
Climate data for Libreville, Gabon in Africa
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Mean daily maximum °C (°F) 29.5
(85.1) 		30.0
(86.0) 		30.2
(86.4) 		30.1
(86.2) 		29.4
(84.9) 		27.6
(81.7) 		26.4
(79.5) 		26.8
(80.2) 		27.5
(81.5) 		28.0
(82.4) 		28.4
(83.1) 		29.0
(84.2) 		28.58
(83.44)
Daily mean °C (°F) 26.8
(80.2) 		27.0
(80.6) 		27.1
(80.8) 		26.6
(79.9) 		26.7
(80.1) 		25.4
(77.7) 		24.3
(75.7) 		24.3
(75.7) 		25.4
(77.7) 		25.7
(78.3) 		25.9
(78.6) 		26.2
(79.2) 		25.95
(78.71)
Mean daily minimum °C (°F) 24.1
(75.4) 		24.0
(75.2) 		23.9
(75.0) 		23.1
(73.6) 		24.0
(75.2) 		23.2
(73.8) 		22.1
(71.8) 		21.8
(71.2) 		23.2
(73.8) 		23.4
(74.1) 		23.4
(74.1) 		23.4
(74.1) 		23.30
(73.94)
Average rainfall mm (inches) 250.3
(9.85) 		243.1
(9.57) 		363.2
(14.30) 		339.0
(13.35) 		247.3
(9.74) 		54.10
(2.13) 		6.600
(0.26) 		13.70
(0.54) 		104.0
(4.09) 		427.2
(16.82) 		490.0
(19.29) 		303.2
(11.94) 		2,841.7
(111.88)
Average rainy days (≥ 0.1 mm) 17.9 14.8 19.5 19.2 16.0 3.70 1.70 4.90 14.5 25.0 22.6 17.6 177.4
Mean monthly sunshine hours 176.7 182.7 176.7 177.0 158.1 132.0 117.8 89.90 96.00 111.6 135.0 167.4 1,720.9
Source: World Meteorological Organization (UN),[4] Hong Kong Observatory[5]

See also

Notes

  1. ^ "Weather Information for Macapa".
  2. ^ Climatological Information for Macapa, Brazil - Hong Kong Observatory
  3. ^ "Weather Information for Pontianak".
  4. ^ "Weather Information for Libreville".
  5. ^ Climatological Information for Libreville, Gabon - Hong Kong Observatory

References

Wikimedia Commons has media related to Equator.


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