World map showing the equator in red

The equator is an imaginary line on the Earth's surface equidistant from the North Pole and South Pole that divides the Earth into a Northern Hemisphere and a Southern Hemisphere. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is subject to the caveats explained below defined as the point in the northern The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the southernmost point on the surface of the Earth. Northern Hemisphere is the half of a Planet that is North of the Equator —the word hemisphere literally means 'half ball' Southern Hemisphere is the half of a Planet that is South of the Equator —the word hemisphere literally means 'half ball' The equators of other planets and astronomical bodies are defined analogously.

Geodesy of the equator

In tourist areas, the equator is often marked on the sides of roads

The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. Ilhéu das Rolas is a small island in São Tomé and Príncipe, in Africa.

A monument marking the equator at the city of Pontianak, Indonesia. Pontianak is the capital of the Indonesia province of West Kalimantan.

The latitude of the equator is, by definition, 0°. Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the The length of Earth's equator is about 40,075. 0 km, or 24,901. The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand 5 miles.

The equator is one of the five main circles of latitude that are based on the relationship between the Earth's axis of rotation and the plane of the Earth's orbit around the sun. A circle of latitude, on the Earth, is an imaginary East - West circle connecting all locations (not taking into account elevation that share a given A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star It is the only line of latitude which is also a great circle. A great circle is a Circle on the surface of a Sphere that has the same circumference as the sphere dividing the sphere into two equal Hemispheres. The imaginary circle obtained when the Earth's equator is projected onto the sky is called the celestial equator. The celestial equator is a Great circle on the imaginary Celestial sphere, in the same plane as the Earth 's Equator.

The Sun, in its seasonal movement through the sky, passes directly over the equator twice each year, on the March and September equinoxes. The Sun (Sol is the Star at the center of the Solar System. A season is one of the major divisions of the Year, generally based on yearly periodic changes in Weather. A year (from Old English gēr) is the time between two recurrences of an event related to the Orbit of the Earth around the Sun An equinox is the event of the Sun passing over the Earth's equator in its annual cycle An equinox is the event of the Sun passing over the Earth's equator in its annual cycle An equinox is the event of the Sun passing over the Earth's equator in its annual cycle At the equator, the rays of the sun are perpendicular to the surface of the earth on these dates. In Geometry, two lines or planes (or a line and a plane are considered perpendicular (or orthogonal) to each other if they form congruent

Places on the equator experience the quickest rates of sunrise and sunset in the world. Sunrise is the instant at which the upper edge of the Sun appears above the Horizon in the East. Sunset, also called sundown in some American English Dialects is the instant when the trailing edge of the Sun 's disk disappears below Such places also have a theoretical constant 12 hours of day and night throughout the year (in practice there are variations of a few minutes due to the effects of atmospheric refraction and because sunrise and sunset are measured from the time the edge of the Sun's disc is on the horizon, rather than its centre). The horizon ( Ancient Greek ὁ ὁρίζων, /ho horídzôn/ from ὁρίζειν, "to limit" is the apparent line that separates North or south of the equator day length increasingly varies with the seasons.

The Earth bulges slightly at the equator. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 An equatorial bulge is a bulge which a planet may have around its Equator, distorting it into an Oblate spheroid. It has an average diameter of 12,750 km, but at the equator the diameter is approximately 43 km greater.

Locations near the equator are good sites for spaceports (e. A spaceport or cosmodrome is a site for launching Spacecraft, by analogy with Seaport for Ships or Airport for Aircraft g. , Guiana Space Centre in Kourou, French Guiana), as they are already moving faster than any other point on the Earth due to the Earth's rotation, and the added velocity reduces the amount of fuel needed to launch spacecraft. The Guiana Space Centre, or more commonly Centre Spatial Guyanais (CSG is a French Spaceport near Kourou in French Guiana. Kourou is a town and commune in French Guiana, an overseas ''région'' and ''département'' of France located in South America French Guiana (Guyane française officially fr ''Guyane'' is an Overseas department (French département d'outre-mer, or DOM) of France (They must be launched to the East to use this effect. )

For high precision work, we find that the equator is not quite as fixed as the above discussion implies. The true equatorial plane must always be perpendicular to the Earth's spin axis. And although this axis is pretty stable, its position wanders in roughly a 9 meter radius circular motion each year. Thus, the true equator moves slightly. This, however, is only important for detailed scientific studies. The effect is quite small, and the width of a line marking the equator on almost any map will be much wider than the error.

Equatorial climate

Temperatures near the equator are high all year round with the exception for periods during the wet season and at higher altitudes. In many tropical regions people identify two seasons: wet and dry. The Tropics are centered on the Equator and limited in Latitude by the Tropic of Cancer in the northern hemisphere at approximately 23°26' (23 A season is one of the major divisions of the Year, generally based on yearly periodic changes in Weather. However, most places close to the equator are wet throughout the year, and seasons can vary depending on a variety of factors including elevation and proximity to an ocean. The elevation of a Geographic location is its height above a fixed reference point often the mean sea level. An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. The rainy and humid conditions mean that the equatorial climate is not the hottest in the world. ^[1]

The surface of the Earth at the equator is mainly ocean. The highest point on the equator is 4,690 m (15,387'), at 00°00′00″S, 77°59′31″W on the south slopes of Volcán Cayambe (summit 5,790 m, 18,996') in Ecuador. For other uses of Cayambe see Cayambe (disambiguation page Cayambe (or Volcán Cayambe) is the name of a Volcano For a topic outline on this subject see List of basic Ecuador topics. This is a short distance above the snow line, and this point and its immediate vicinity form the only section of the equator where snow lies on the ground. The snow line is the point above which or poleward of which snow and ice cover the ground throughout the year "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation.

Equatorial countries and territories

The equator traverses the land and/or territorial waters of 14 countries. In Political geography and International politics, a country is a Political division of a geographical entity Starting at west Africa and moving east, these are:

• São Tomé and Príncipe – passing through Ilhéu das Rolas, an islet in this archipelago
• Gabon
• Republic of the Congo
• Democratic Republic of the Congo
• Uganda – including some islets in Lake Victoria
• Kenya
• Somalia
• Maldives – misses every island, passing between Gaafu Dhaalu Atoll and Gnaviyani Atoll
• Indonesia – crosses many islands, most notably Sumatra, Borneo, Sulawesi, and Halmahera
• Kiribati – misses every island, passing between Aranuka and Nonouti Atolls in the Gilbert Islands
• Baker Island (unincorporated territory of the United States) – passes through territorial waters (NB the equator also passes through the exclusive economic zones around Howland Island and Jarvis Island, but not through their territorial waters)
• Ecuador (literal translation of its official name is "Republic of the Equator") – including Isabela Island in the Galápagos Islands. São Tomé and Príncipe, officially the Democratic Republic of São Tomé and Príncipe, is an Island nation in the Gulf of Guinea, off the western equatorial Ilhéu das Rolas is a small island in São Tomé and Príncipe, in Africa. For human anatomy see Islets of Langerhans An islet is a small Island. Gabon (gəˈbɒn or /gaˈbõ/ in French) is a country in west central Africa sharing borders with Equatorial Guinea, Cameroon, Republic The Republic of the Congo (République du Congo Kongo: Repubilika ya Kongo; Lingala: Republiki ya Kongó) also known as Congo-Brazzaville The Democratic Republic of the Congo (République démocratique du Congo often referred to as DR Congo, DRC or RDC, and formerly known or referred to The Republic of Uganda is a Landlocked country in East Africa. Lake Victoria or Victoria Nyanza (also known as Ukerewe and Nalubaale) is one of the Great Lakes of Africa. The Republic of Kenya is a country in East Africa. It is bordered by Ethiopia to the north Somalia to the northeast Tanzania to the south Somalia ( Soomaaliya; الصومال) officially the Somali Republic ( Jamhuuriyadda Soomaaliya, جمهورية الصومال) and formerly known The Maldives ( or, or Maldive Islands) officially the Republic of Maldives, is an Island nation consisting of a group of atolls stretching An island (ˈaɪlənd or isle (/ˈaɪl/ is any piece of land that is completely surrounded by water in two dimensions above high tide and isolated from other significant Southern Huvadhu Atoll or Gaafu Dhaalu is an Administrative district of the Maldives formed by the southwestern section of Huvadhu Atoll Gnaviyani Atoll is one of the administrative divisions of the Maldives. The Republic of Indonesia ( (Republik Indonesia is a Country in Southeast Asia. Sumatra (also spelled Sumatera) is the sixth largest island in the world (approximately 470000 km² and is the largest island entirely in Indonesia (two Borneo is the third largest island in the world and is located at the centre of Maritime Southeast Asia. Sulawesi (formerly known as Celebes, ˈsɛlɛbiz is one of the four larger Sunda Islands of Indonesia and is situated between Borneo and the Halmahera (also Jilolo or Gilolo is the largest Island in the Maluku Islands. Kiribati or ( kirr-i-bas or KEE-ree-buhss ˈkiɾibas in Gilbertese) officially the Republic of Kiribati, is an Island nation located in Aranuka (also previously known as Henderville Nonouki or Starbuck is an Atoll of Kiribati, located just north of the Equator, in the Gilbert Islands Nonouti is an Atoll and District of Kiribati. The atoll is located in the South Gilbert Islands, 38 km north of Tabiteuea and 250 km south Baker Island is an uninhabited Atoll located just north of the Equator in the central Pacific Ocean about 3100 km (1670  nmi) southwest The United States of America —commonly referred to as the Under the law of the sea, an Exclusive Economic Zone ( EEZ) is a seazone over which a State has special rights over the exploration and use of marine WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout Jarvis Island (also formerly known as Bunker Island) is an uninhabited 4 For a topic outline on this subject see List of basic Ecuador topics. Isabela Island is the largest island of the Galápagos with an area of 4640 km²and length of 80 miles (100km nearly 4 times larger than Santa Cruz the Ecuador's capital, Quito, is 13 km south of the equator. Quito, officially San Francisco de Quito, is the Capital of Ecuador in northwestern South America.
• Colombia - mostly through the jungles of the south. Colombia (kəˈlʌmbɪə officially the Republic of Colombia () is a country in northwestern South America. Jungle usually refers to a dense Forest in a hot climate such as a Tropical rainforest.
• Brazil – including some islands in the mouth of the Amazon River and passing through Macapá, capital of Amapá state

Despite its name, no part of Equatorial Guinea's territory lies on the equator. |utc_offset = -2 to -4 |time_zone_DST = BRST |utc_offset_DST = -2 to -5 |cctld The Amazon River (Rio Amazonas Río Amazonas of South America is the largest river in the world by volume with a total river flow greater than the next top ten largest rivers Macapá (mekepä´ is the capital of the state of Amapá in Brazil, (2005 pop Amapá (amaˈpa is one of the states of Brazil, located in the extreme north bordering French Guiana and Suriname to the north The Republic of Equatorial Guinea ( República de Guinea Ecuatorial,) is a country in Central Africa. However, its island of Annobón is about 100 miles (155 km) south of the equator, and the rest of the country lies to the north

"Crossing the Line"

Main article: Line-crossing ceremony

The English-speaking seafaring tradition maintains that all sailors who cross the equator during a nautical voyage must undergo rites of passage and elaborate rituals initiating them into The Solemn Mysteries of the Ancient Order of the Deep. Annobón (or Annabon or Anabon; from Ano bom Portuguese for Good Year) also known as Pagalu or Pigalu, is an The ceremony of Crossing the Line is an initiation Rite in the Royal Navy, U These rituals date back to the Middle Ages, though the current ceremonies are most likely derived from Viking traditions. A Viking is one of the Norse ( Scandinavian Explorers Warriors Merchants, and pirates who raided and colonized wide areas Those who have never "crossed the line" are derisively referred to as "pollywogs" or simply "slimy wogs". Upon entering the domain of His Royal Majesty, Neptunus Rex, all wogs are subject to various initiation rituals performed by those members of the crew who have made the journey before. Upon completion of the initiation ceremony, the wogs are then known as "trusty Shellbacks". If the crossing of the equator is done at the 180th meridian, the title of "Golden Shellback" is conferred, recognizing the simultaneous entry into the realm of the Golden Dragon. The 180th meridian or antimeridian is the meridian defined as 180° longitude If the crossing occurs at the Greenwich or Prime Meridian, the sailor is considered to be an "Emerald Shellback". The Prime Meridian is the meridian (line of Longitude) at which longitude is defined to be 0° ^[2]

Exact length of the equator

The equator is modeled exactly in two widely used standards as a circle of radius an integer number of meters. In 1976 the IAU standardized this radius as 6,378,140 m, subsequently refined by the IUGG to 6,378,137 m and adopted in WGS-84, though the yet more recent IAU-2000 has retained the old IAU-1976 value. The International Union of Geodesy and Geophysics, or IUGG, is a Non-governmental organisation dedicated to the scientific study of the Earth using The World Geodetic System defines a reference frame for the earth for use in Geodesy and Navigation. In either case the length of the equator is by definition exactly 2π times the given standard, which to the nearest millimeter is 40,075,016. 686 m in WGS-84 and 40,075,035. The World Geodetic System defines a reference frame for the earth for use in Geodesy and Navigation. 535 m in IAU-1976 and IAU-2000.

(Although millimeter precision can be important up to the scale of a mile, it has negligible physical significance at the scale of a geographic feature such as the equator. From a computational standpoint however millimeter precision or better can be valuable for maintaining consistent results when used in programs for surveying etc. As an overly simple example, if a program were to convert back and forth between the radius and the circumference of the earth sufficiently often while maintaining precision only to a meter each time, errors might accumulate until they became noticeable. )

The geographical mile is defined as one arc minute of the equator, and therefore has different values depending on which standard equator is used, namely 1855. The geographical mile is a unit of length determined by 1 minute of arc along the Earth 's Equator, approximately equal to 1855 3248 m or 1855. 3257 m for respectively WGS-84 and IAU-2000, a difference of nearly a millimeter.

The earth is standardly modeled as a sphere flattened about 0. 336% along its axis. This results in the equator being about 0. 16% longer than a meridian (as a great circle passing through the two poles). This article is about the geographical concept For other uses of the word see Meridian. The IUGG standard meridian is to the nearest millimeter 40,007,862. 917 m, one arc minute of which is 1852. 216 m, explaining the SI standardization of the nautical mile as 1852 m, more than 3 meters short of the geographical mile. A nautical mile or sea mile is a unit of Length. It corresponds approximately to one minute of Latitude along any meridian. The geographical mile is a unit of length determined by 1 minute of arc along the Earth 's Equator, approximately equal to 1855

Notes and references

• Moritz, H. (1980). "Geodetic Reference System". Bulletin Geodesique 54 (3).   (IUGG/WGS-84 data)
• Taff, Laurence G. (1981). Computational Spherical Astronomy. John Wiley and Sons.   (IAU data)

See also