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equator
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{{Short description|Intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and midway between the poles}}{{Other uses}}{{pp-move-indef}}{{Location map-line|lat=0|caption=Equator in the map of Earth}}File:Equator and Prime Meridian.svg|thumb|upright=1.35|Nations or territories that touch the equator (red) or the IERS Reference MeridianIERS Reference MeridianThe equator of a rotating spheroid (such as a planet) is the parallel (circle of latitude) at which latitude is defined to be 0°. It is the imaginary line on the spheroid, equidistant from its poles, dividing it into northern and southern hemispheres. In other words, it is the intersection of the spheroid with the plane perpendicular to its axis of rotation and midway between its geographical poles.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.

Etymology

The name is derived from medieval Latin word aequator, in the phrase circulus aequator diei et noctis, meaning ‘circle equalizing day and night’, from the Latin word aequare meaning ‘make equal’.WEB,weblink Definition of equator, OxfordDictionaries.com, 5 May 2018,

Overview

{{multiple image| align = right| image1 = Equator monument.jpg| width1 = 150| alt1 = | caption1 = | image2 = Equator sign kenya.jpg| width2 = 125| alt2 = | caption2 = | footer = Left: A monument marking the equator near the city of Pontianak, IndonesiaRight: Road sign marking the equator near Nanyuki, Kenya}}The latitude of the Earth's equator is, by definition, 0° (zero degrees) of arc. The equator is one of the five notable circles of latitude on Earth; the other four are both polar circles (the Arctic Circle and the Antarctic Circle) and both 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.In the cycle of Earth's seasons, the equatorial plane runs through the Sun twice per year: on the equinoxes in March and September. To a person on Earth, the Sun 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 solar noon on the equator.File:Equator Sao Tome.jpg|thumb|left|The equator marked as it crosses Ilhéu das Rolas, in São Tomé and PríncipeSão Tomé and PríncipeFile:equator Line Monument, Macapá city, Brazil.jpg|left|thumb|The Marco Zero monument marking the equator in Macapá, BrazilBrazilLocations on the equator experience the shortest sunrises and sunsets because the Sun's 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.Earth 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.WEB,weblink Equator, National Geographic - Education, 29 May 2013, Sites near the equator, such as the Guiana Space Centre in Kourou, French Guiana, are good locations for spaceports as they have a fastest rotational speed of any latitude, 460 m/s. The added velocity reduces the fuel needed to launch spacecraft eastward (in the direction of Earth's rotation) to orbit, while simultaneously avoiding costly maneuvers to flatten inclination during missions such as the Apollo moon landings.WEB, William Barnaby Faherty, Charles D. Benson, Moonport: A History of Apollo Launch Facilities and Operations,weblink NASA Special Publication-4204 in the NASA History Series, 8 May 2019,weblink 29 April 2019, Chapter 1.2: A Saturn Launch Site, 1978, Equatorial launch sites offered certain advantages over facilities within the continental United States. A launching due east from a site on the equator could take advantage of the earth's maximum rotational velocity (460 meters per second) to achieve orbital speed. The more frequent overhead passage of the orbiting vehicle above an equatorial base would facilitate tracking and communications. Most important, an equatorial launch site would avoid the costly dogleg technique, a prerequisite for placing rockets into equatorial orbit from sites such as Cape Canaveral, Florida (28 degrees north latitude). The necessary correction in the space vehicle's trajectory could be very expensive - engineers estimated that doglegging a Saturn vehicle into a low-altitude equatorial orbit from Cape Canaveral used enough extra propellant to reduce the payload by as much as 80%. In higher orbits, the penalty was less severe but still involved at least a 20% loss of payload., live,

Geodesy

{{further|Earth ellipsoid|Reference ellipsoid}}

Precise location

The precise location of the equator is not truly fixed; the true equatorial plane is perpendicular to the Earth's spin axis, which drifts about {{convert|9|m|0}} during a year. This effect must be accounted for in detailed geophysical measurements.{{citation needed|date=April 2017}}

Exact length

The International Association of Geodesy (IAG) and the International Astronomical Union (IAU) have chosen to use an equatorial radius of 6,378.1366 kilometres (3,963.1903 mi) (codified as the IAU 2009 value).The IAU 2009 system of astronomical constants: This equatorial radius is also in the 2003 and 2010 IERS Conventions.IERS Conventions It is also the equatorial radius used for the IERS 2003 ellipsoid. If it were really circular, the length of the equator would then be exactly 2π times the radius, namely 40,075.0142 kilometres (24,901.4594 mi). The GRS 80 (Geodetic Reference System 1980) as approved and adopted by the IUGG at its Canberra, Australia meeting of 1979 has an equatorial radius of 6,378.137 kilometres (3,963.191 mi). The WGS 84 (World Geodetic System 1984) which is a standard for use in cartography, geodesy, and satellite navigation including GPS, also has an equatorial radius of 6,378.137 kilometres (3,963.191 mi). For both GRS 80 and WGS 84, this results in a length for the equator of 40,075.0167 km (24,901.4609 mi). 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}}).The earth is commonly modeled as a sphere flattened 0.336% along its axis. This makes the equator 0.16% longer than a 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 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}}

Equatorial countries and territories

{{kml}}File:ECSundialGPS.jpg|thumb|upright|GPS reading taken on the equator close to the Quitsato Sundial, at Mitad del Mundo, EcuadorEcuadorThe equator passes through the land of 11 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
{{CoordNEname=Prime Meridian}}! scope="row" style="background:#b0e0e6;" | Atlantic Ocean Gulf of Guinea, "Null Island"
0N31type:country|name=São Tomé and Príncipe}}! scope="row" | {{STP}}| Passing through Pestana Equador resort on the Ilhéu das Rolas
0N21type:country|name=Gabon}}! scope="row" | {{GAB}}8.9abbr=on}} south of Ayem, {{convertkm|abbr=on}} north of Mayene, Booue
0N56type:country|name=Republic of the Congo}}! scope="row" | {{COG}}| Passing through the town of Makoua.
0N46type:country|name=Democratic Republic of the Congo}}! scope="row" | {{COD}}9abbr=on}} south of central Butembo
0N43type:country|name=Uganda}}! scope="row" | {{UGA}}32abbr=on}} south of central Kampala
{{Coord032Ename=Lake Victoria}}! scope="row" style="background:#b0e0e6;" | Lake Victoria Passing through some islands of {{UGA}} in Mukono District and Namayingo District
0N0type:country|name=Kenya}}! scope="row" | {{KEN}}6abbr=on}} north of central Kisumu
0N0type:country|name=Somalia}}! scope="row" | {{SOM}}| Passing south of Jamame
{{Coord042Ename=Indian Ocean}}! scope="row" style="background:#b0e0e6;" | Indian Ocean Passing between Huvadhu Atoll and Fuvahmulah of the {{MDV}}
0N12type:country|name=Indonesia}}! scope="row" | {{IDN}}| The Batu Islands, Sumatra and the Lingga Islands
{{Coord0104Ename=Karimata Strait}}! scope="row" style="background:#b0e0e6;" | Karimata Strait
0N9type:country|name=Indonesia}}! scope="row" | {{IDN}}Borneo (passing through Pontianak, Indonesia>Pontianak)
{{Coord0117Ename=Makassar Strait}}! scope="row" style="background:#b0e0e6;" | Makassar Strait
0N40type:country|name=Indonesia}}! scope="row" | {{IDN}}Sulawesi>Sulawesi (Celebes)
{{Coord0120Ename=Gulf of Tomini}}! scope="row" style="background:#b0e0e6;" | Gulf of Tomini
{{Coord0124Ename=Molucca Sea}}! scope="row" style="background:#b0e0e6;" | Molucca Sea
0N24type:country|name=Indonesia}} ! scope="row" | {{IDN}}|Kayoa and Halmahera islands
{{Coord0127Ename=Halmahera Sea}}! scope="row" style="background:#b0e0e6;" | Halmahera Sea
0N20type:country|name=Indonesia}}! scope="row" | {{IDN}}| Gebe and Kawe islands
{{Coord0129Ename=Pacific Ocean}}! scope="row" style="background:#b0e0e6;" | Pacific Ocean Passing between Aranuka and Nonouti atolls, {{KIR}} (at {{Coord0173E}})
0N6type:country|name=Ecuador}}! scope="row" | {{ECU}}24abbr=on}} north of central Quito, near Ciudad Mitad del Mundo, and precisely at the location of Catequilla, a Pre-Columbian era>pre-Columbian ruin. Also, Isabela Island in the Galápagos Islands
0N32type:country|name=Colombia}}! scope="row" | {{COL}}4.3abbr=on}} north of the border with Peru
valign="top"
0N3type:country|name=Brazil}}! scope="row" | {{BRA}}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 monument and the Avenue Equatorial)
{{Coord049Wname=Atlantic Ocean}}! scope="row" style="background:#b0e0e6;" | Atlantic Ocean At the Perigoso Canal ((:sv:Canal Perigoso|sv)) on the mouth of the Amazon River
Despite its name, no part of Equatorial Guinea lies on the equator. However, its island of Annobón is {{convert|155|km|abbr=on}} south of the equator, and the rest of the country lies to the north.

Equatorial seasons and climate

File:seasons.svg|frame|right|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 incident light, the dissipation of light in the atmosphere is greater when it falls at a shallow angle.]]Seasons result from the tilt of the Earth's axis compared to the plane of its revolution around the Sun. Throughout the year the northern and southern hemispheres are alternately turned either toward or away from the sun depending on Earth's position in its orbit. The hemisphere turned 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 equinoxes, the Earth's axis is perpendicular to the sun rather than tilted toward or away, meaning that day and night are both about 12 hours long across the whole of the Earth.The equator lies mostly on the three largest oceans: the Atlantic Ocean, the Indian Ocean, and the Pacific Ocean. Near the equator there is little temperature change throughout the year, though there may be dramatic differences in rainfall and humidity. The terms summer, autumn, winter and spring do not generally apply. 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 climates with a dry season in the middle of the year, and the Somali Current generated by the Asian monsoon due to continental heating via the high Tibetan Plateau causes Greater Somalia to have an arid climate despite its equatorial location.Average annual temperatures in equatorial lowlands are around {{convert|31|°C|°F|abbr=on}} during the afternoon and {{convert|23|°C|°F|abbr=on}} around sunrise. Rainfall is very high away from cold current upwelling zones, from {{convert|2500|to|3500|mm|abbr=on|round=5}} per year. There are about 200 rainy days per year and average annual sunshine hours are around 2,000. Despite high year-round sea level temperatures, some higher altitudes such as the Andes and Mount Kilimanjaro have glaciers. 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}} lower than on Mount Everest and as much as {{convert|2000|m|ft}} lower than the highest snow line in the world, near the Tropic of Capricorn on Llullaillaco.{{Weather box|location = Macapá, Brazil in South America|metric first = yes|single line = yes|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 = 2336.1World Meteorological Organization (United Nations>UN),WEB
,weblink
, Weather Information for Macapa
, Hong Kong ObservatoryClimatological Information for Macapa, Brazil - Hong Kong Observatory|date=March 2011}}
{{Weather box|location = Pontianak, Indonesia in Asia|metric first = yes|single line = yes|Jan high C = 32.4|Feb high C = 32.7|Mar high C = 32.9|Apr high C = 33.2|May high C = 33.0|Jun high C = 33.2|Jul high C = 32.9|Aug high C = 33.4|Sep high C = 32.6|Oct high C = 32.6|Nov high C = 32.2|Dec high C = 32.0|year high C = 32.7|Jan mean C = 27.6|Feb mean C = 27.7|Mar mean C = 28.0|Apr mean C = 28.2|May mean C = 28.2|Jun mean C = 28.2|Jul mean C = 27.7|Aug mean C = 27.9|Sep mean C = 27.6|Oct mean C = 27.7|Nov mean C = 27.4|Dec mean C = 27.2|year mean C = 27.7|Jan low C = 22.7|Feb low C = 22.6|Mar low C = 23.0|Apr low C = 23.2|May low C = 23.4|Jun low C = 23.1|Jul low C = 22.5|Aug low C = 22.3|Sep low C = 22.6|Oct low C = 22.8|Nov low C = 22.6|Dec low C = 22.4|year low C = 22.7|rain colour=green|Jan rain mm = 260|Feb rain mm = 215|Mar rain mm = 254|Apr rain mm = 292|May rain mm = 256|Jun rain mm = 212|Jul rain mm = 201|Aug rain mm = 180|Sep rain mm = 295|Oct rain mm = 329|Nov rain mm = 400|Dec rain mm = 302|Jan rain days = 15|Feb rain days = 13|Mar rain days = 21|Apr rain days = 22|May rain days = 20|Jun rain days = 18|Jul rain days = 16|Aug rain days = 25|Sep rain days = 14|Oct rain days = 27|Nov rain days = 25|Dec rain days = 22|unit rain days = 0.1 mmWorld Meteorological Organization (United Nations>UN)WEB
,weblink
, Weather Information for Pontianak
, |date=March 2011}}
{{Weather box|location = Libreville, Gabon in Africa|metric first = yes|single line = yes|Jan high C = 29.5|Feb high C = 30.0|Mar high C = 30.2|Apr high C = 30.1|May high C = 29.4|Jun high C = 27.6|Jul high C = 26.4|Aug high C = 26.8|Sep high C = 27.5|Oct high C = 28.0|Nov high C = 28.4|Dec high C = 29.0|year high C = 28.58|Jan mean C = 26.8|Feb mean C = 27.0|Mar mean C = 27.1|Apr mean C = 26.6|May mean C = 26.7|Jun mean C = 25.4|Jul mean C = 24.3|Aug mean C = 24.3|Sep mean C = 25.4|Oct mean C = 25.7|Nov mean C = 25.9|Dec mean C = 26.2|year mean C = 25.95|Jan low C = 24.1|Feb low C = 24.0|Mar low C = 23.9|Apr low C = 23.1|May low C = 24.0|Jun low C = 23.2|Jul low C = 22.1|Aug low C = 21.8|Sep low C = 23.2|Oct low C = 23.4|Nov low C = 23.4|Dec low C = 23.4|year low C = 23.30|rain colour=green|Jan rain mm = 250.3|Feb rain mm = 243.1|Mar rain mm = 363.2|Apr rain mm = 339.0|May rain mm = 247.3 |Jun rain mm = 54.10|Jul rain mm = 6.600|Aug rain mm = 13.70|Sep rain mm = 104.0|Oct rain mm = 427.2|Nov rain mm = 490.0|Dec rain mm = 303.2|Jan rain days = 17.9|Feb rain days = 14.8|Mar rain days = 19.5|Apr rain days = 19.2|May rain days = 16.0|Jun rain days = 3.70|Jul rain days = 1.70|Aug rain days = 4.90|Sep rain days = 14.5|Oct rain days = 25.0|Nov rain days = 22.6|Dec rain days = 17.6|unit rain days = 0.1 mm|Jan sun = 176.7|Feb sun = 182.7|Mar sun = 176.7|Apr sun = 177.0|May sun = 158.1|Jun sun = 132.0|Jul sun = 117.8|Aug sun = 89.90|Sep sun = 96.00|Oct sun = 111.6|Nov sun = 135.0|Dec sun = 167.4|year sun = 1720.9World Meteorological Organization (United Nations>UN),WEB
,weblink
, Weather Information for Libreville
, Hong Kong ObservatoryClimatological Information for Libreville, Gabon - Hong Kong Observatory|date=March 2011}}

Line crossing ceremonies

There is a widespread maritime tradition of holding ceremonies to mark a sailor's first crossing of the equator. In the past, these ceremonies have been notorious for their brutality, especially in naval practice. {{citation needed|date=April 2017}} Milder line-crossing ceremonies, typically featuring King Neptune, are also held for passengers' entertainment on some civilian ocean liners and cruise ships.{{citation needed|date=January 2015}}

See also

{{div col|colwidth=30em}} {{div col end}}

References

{{reflist}}

Sources

{{Commons category|Equator}}
  • JOURNAL, Geodetic Reference System 1980, Bulletin Géodésique, Springer-Verlag, Berlin, H, Moritz, 395–405, 54, 3, September 1980, 10.1007/BF02521480, 1980BGeod..54..395M, (IUGG/WGS-84 data)
  • BOOK, Computational Spherical Astronomy, Wiley, New York City, New York, Laurence G, Taff, 1981, 0-471-06257-X, 6532537, (IAU data)
{{geographical coordinates|state=collapsed}}

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