Equator

# Equator

Overview
An equator is the intersection of a sphere
Sphere
A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...

's surface with the plane
Plane (mathematics)
In mathematics, a plane is a flat, two-dimensional surface. A plane is the two dimensional analogue of a point , a line and a space...

perpendicular to the sphere's axis of rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...

and containing the sphere's center of mass
Center of mass
In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...

.
Discussion

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Encyclopedia
An equator is the intersection of a sphere
Sphere
A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...

's surface with the plane
Plane (mathematics)
In mathematics, a plane is a flat, two-dimensional surface. A plane is the two dimensional analogue of a point , a line and a space...

perpendicular to the sphere's axis of rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...

and containing the sphere's center of mass
Center of mass
In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...

.

The Equator refers to the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's equator and is an imaginary line on the Earth's surface equidistant from the North Pole
North Pole
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 hemisphere where the Earth's axis of rotation meets its surface...

and South Pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...

, dividing the Earth into the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

and Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

. Other planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

s and spherical astronomical bodies have equators similarly defined.

## Geodesy of the Equator

The latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

of the Equator is 0° (zero degree
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...

s). The length of Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's equator is about 40030.2 kilometres (24,873.7 mi). To calculate the actual length of the Equator would require taking into consideration that the Equator goes up and down various mountains and hills in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

, in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

, and on various islands. The Equator is one of the five notable circles of latitude
Circle of latitude
A circle of latitude, on the Earth, is an imaginary east-west circle connecting all locations that share a given latitude...

on Earth, with the others being the two Polar Circle
Polar circle
A polar circle is either the Arctic Circle or the Antarctic Circle. On Earth, the Arctic Circle is located at a latitude of  N, and the Antarctic Circle is located at a latitude of  S....

s and the two Tropical Circles: the Tropic of Cancer
Tropic of Cancer
The Tropic of Cancer, also referred to as the Northern tropic, is the circle of latitude on the Earth that marks the most northerly position at which the Sun may appear directly overhead at its zenith...

and the Tropic of Capricorn
Tropic of Capricorn
The Tropic of Capricorn, or Southern tropic, marks the most southerly latitude on the Earth at which the Sun can be directly overhead. This event occurs at the December solstice, when the southern hemisphere is tilted towards the Sun to its maximum extent.Tropic of Capricorn is one of the five...

. The Equator is the only line of latitude which is also a great circle
Great circle
A great circle, also known as a Riemannian circle, of a sphere is the intersection of the sphere and a plane which passes through the center point of the sphere, as opposed to a general circle of a sphere where the plane is not required to pass through the center...

. The imaginary circle obtained when the Earth's equator is projected onto the sky is called the celestial equator
Celestial equator
The celestial equator is a great circle on the imaginary celestial sphere, in the same plane as the Earth's equator. In other words, it is a projection of the terrestrial equator out into space...

.

The Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

, in its season
Season
A season is a division of the year, marked by changes in weather, ecology, and hours of daylight.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...

al apparent movement across the sky, passes directly over the Equator twice each year
Year
A year is the orbital period of the Earth moving around the Sun. For an observer on Earth, this corresponds to the period it takes the Sun to complete one course throughout the zodiac along the ecliptic....

, at the March and September equinox
Equinox
An equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator...

es. At the Equator, the rays of the sun are perpendicular
Perpendicular
In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...

to the surface of the earth on these dates.

Places on the Equator experience the quickest rates of sunrise
Sunrise
Sunrise is the instant at which the upper edge of the Sun appears above the horizon in the east. Sunrise should not be confused with dawn, which is the point at which the sky begins to lighten, some time before the sun itself appears, ending twilight...

and sunset
Sunset
Sunset or sundown is the daily disappearance of the Sun below the horizon in the west as a result of Earth's rotation.The time of sunset is defined in astronomy as the moment the trailing edge of the Sun's disk disappears below the horizon in the west...

in the world. They are also the only places in the world where the sun can go directly from the zenith
Zenith
The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e...

The nadir is the direction pointing directly below a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface there. Since the concept of being below is itself somewhat vague, scientists define the nadir in more rigorous...

and from the nadir to the zenith. Such places also have a theoretical constant 12 hours of day and night throughout the year, though 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 that the edge of the Sun's disk is on the horizon
Horizon
The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...

, rather than the center of the disk.

The Earth bulges slightly at the Equator
Equatorial bulge
An equatorial bulge is a difference between the equatorial and polar diameters of a planet, due to the centrifugal force of its rotation. A rotating body tends to form an oblate spheroid rather than a sphere...

. It has an average diameter of 12750 kilometres (7,923 mi), but at the Equator the diameter is approximately 43 kilometres (27 mi) greater than the polar diameter.

Locations near the Equator are theoretically good sites for spaceport
Spaceport
A spaceport or cosmodrome is a site for launching spacecraft, by analogy with seaport for ships or airport for aircraft. The word spaceport, and even more so cosmodrome, has traditionally been used for sites capable of launching spacecraft into orbit around Earth or on interplanetary trajectories...

s, such as the Guiana Space Centre in Kourou
Kourou
Kourou is a commune in French Guiana, an overseas region and department of France located in South America.Kourou is the location of the Guiana Space Centre, France and ESA's main spaceport.-Geography:...

, French Guiana
French Guiana
French Guiana is an overseas region of France, consisting of a single overseas department located on the northern Atlantic coast of South America. It has borders with two nations, Brazil to the east and south, and Suriname to the west...

, 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. Spacecraft launched in this manner must launch to the east, southeast, or northeast to take advantage of this effect.

For high precision work, 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. Although this axis is relatively stable, its position drifts
Polar motion
Polar motion of the earth is the movement of Earth's rotational axis across its surface. This is measured with respect to a reference frame in which the solid Earth is fixed...

about 9 metres (30 ft) north-south over the course of a year. Thus, the true equator moves slightly, but this effect is only relevant in extremely precise geophysical measurements.

## Equatorial seasons and climate

Near the Equator there is little distinction between summer, winter, autumn, or spring. The temperatures there are usually high year-round—with the distinct exception of parts of the Equator that cross high mountains in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

and in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

. (See Andes Mountains and Mt. Kilimanjaro.) The temperature at the Equator can also plummet during the extensive rainstorms in many locations. In many tropical regions people identify two seasons: the wet season and the dry season. However, many places close to the Equator are on the oceans or rainy throughout the year. The seasons can vary depending on a variety of factors including elevation and proximity to an ocean. These oceanic, rainy, and mountainous locations mean that the equatorial climate is not the hottest in the world.

The surface of the Earth at the Equator lies mostly on three of the ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

s: the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

, the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

, and the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

. The highest point on the Equator is at the elevation of 4690 metres (15,387 ft), at 0°0′0"N 77°59′31"W, found on the southern slopes of Volcán Cayambe [summit 5790 metres (18,996 ft)] in Ecuador
Ecuador , officially the Republic of Ecuador is a representative democratic republic in South America, bordered by Colombia on the north, Peru on the east and south, and by the Pacific Ocean to the west. It is one of only two countries in South America, along with Chile, that do not have a border...

. This place is a short distance above the snow line
Snow line
The climatic snow line is the point above which snow and ice cover the ground throughout the year. The actual snow line may seasonally be significantly lower....

, and this immediate vicinity forms the only section of the Equator where snow lies on the ground year-round.

## Equatorial countries and territories

The Equator traverses the land and/or territorial waters of 14 countries
Country
A country is a region legally identified as a distinct entity in political geography. A country may be an independent sovereign state or one that is occupied by another state, as a non-sovereign or formerly sovereign political division, or a geographic region associated with a previously...

. Starting at the Prime Meridian
Prime Meridian
The Prime Meridian is the meridian at which the longitude is defined to be 0°.The Prime Meridian and its opposite the 180th meridian , which the International Date Line generally follows, form a great circle that divides the Earth into the Eastern and Western Hemispheres.An international...

and heading eastwards, the Equator passes through:
Co-ordinates Country, territory or sea Notes
0°N 0°E Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

Gulf of Guinea
Gulf of Guinea
The Gulf of Guinea is the northeasternmost part of the tropical Atlantic Ocean between Cape Lopez in Gabon, north and west to Cape Palmas in Liberia. The intersection of the Equator and Prime Meridian is in the gulf....

0°0′N 6°31′E Ilhéu das Rolas
Ilhéu das Rolas
Ilhéu das Rolas is a small island in São Tomé and Príncipe, in Africa. The island lies on the equator, off the southern tip of São Tomé Island. It is in the Caué District of São Tomé Province. The island is home to a small resort....

0°0′N 6°31′E Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

Gulf of Guinea
Gulf of Guinea
The Gulf of Guinea is the northeasternmost part of the tropical Atlantic Ocean between Cape Lopez in Gabon, north and west to Cape Palmas in Liberia. The intersection of the Equator and Prime Meridian is in the gulf....

0°0′N 9°21′E
0°0′N 13°56′E
0°0′N 17°46′E
0°0′N 29°43′E
0°0′N 32°22′E Lake Victoria
Lake Victoria
Lake Victoria is one of the African Great Lakes. The lake was named for Queen Victoria of the United Kingdom, by John Hanning Speke, the first European to discover this lake....

Passing through some islands of
0°0′N 34°0′E
0°0′N 41°0′E
0°0′N 42°53′E Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

Passing between Huvadhu Atoll and Fuvahmulah of the
0°0′N 98°12′E The Batu Islands
Batu Islands
The Batu Islands are an archipelago of Indonesia located in the Indian Ocean off the west coast of Sumatra, between Nias and Siberut. The three primary islands, of approximately equal size, are Pini, Tanahmasa, and Tanahbala. There are forty-eight smaller islands, of which less than half are...

, Sumatra
Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...

and the Lingga Islands
Lingga Islands
Not to be confused with "Linga", a common Scottish island name, see Linga The Lingga Islands or Lingga Archipelago are a group of islands in Indonesia, located south of Singapore, along both sides of the equator, off the eastern coast of Riau Islands province on Sumatra island...

0°0′N 104°34′E Karimata Strait
Karimata Strait
The Karimata Strait is the wide strait that connects the South China Sea to the Java Sea, dividing the islands of Sumatra from Borneo , both in Indonesia....

0°0′N 109°9′E Borneo
Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....

0°0′N 117°30′E Makassar Strait
Makassar Strait
Makassar Strait is a strait between the islands of Borneo and Sulawesi in Indonesia. To the north it joins the Celebes Sea, while to the south it meets the Java Sea.The Mahakam River of Borneo empties into the strait....

0°0′N 119°40′E Sulawesi (Celebes)
Sulawesi
Sulawesi is one of the four larger Sunda Islands of Indonesia and is situated between Borneo and the Maluku Islands. In Indonesia, only Sumatra, Borneo, and Papua are larger in territory, and only Java and Sumatra have larger Indonesian populations.- Etymology :The Portuguese were the first to...

0°0′N 120°5′E Gulf of Tomini
Gulf of Tomini
The Gulf of Tomini is a gulf near the island of Sulawesi, Indonesia.It is bounded on its north and west sides by the Minahassa Peninsula and on the south side by the East Peninsula, Sulawesi....

0°0′N 124°0′E Molucca Sea
Molucca Sea
The Molucca Sea is located in the western Pacific Ocean, within the country of Indonesia. The region is rich in coral and has many diving sites.-Location:...

0°0′N 127°24′E Kayoa and Halmahera
Halmahera
Halmahera is the largest island in the Maluku Islands. It is part of the North Maluku province of Indonesia.Halmahera has a land area of 17,780 km² and a population in 1995 of 162,728...

islands
0°0′N 127°53′E Halmahera Sea
Halmahera Sea
Halmahera Sea is a regional sea located in the central eastern part of the Australasian Mediterranean Sea. It is centered at about 1°S and 129°E and is bordered by the Pacific Ocean to the north, Halmahera to the west, Waigeo and Irian Jaya to the east, and the Seram Sea to the south...

0°0′N 129°20′E Gebe Island
0°0′N 129°21′E Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

Passing 570 m north of Waigeo
Waigeo
Waigeo is an island in West Papua province of eastern Indonesia. The island is also known as Amberi, or Waigiu. It is the largest of the four main islands in the Raja Ampat Islands archipelago, between Halmahera and about 65 km to the northwest coast of New Guinea...

island,
> Passing 13 km south of Aranuka
Aranuka
Aranuka is an atoll of Kiribati, located just north of the equator, in the Gilbert Islands...

atoll,
> Passing 21 km south of Baker Island
Baker Island
Baker Island is an uninhabited atoll located just north of the equator in the central Pacific Ocean about southwest of Honolulu. The island lies almost halfway between Hawaii and Australia, and is a possession of the United States. Its nearest neighbor is Howland Island, to the north.Located at...

,
0°0′N 91°35′W Isabela Island
Isabela Island is the largest island of the Galápagos with an area of , and length of nearly 4 times larger than Santa Cruz, the next largest of the islands. This island was named in honor of Queen Isabella of Spain, who sponsored the voyage of Columbus. . By the English, it was named Albemarle...

in the Galápagos Islands
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...

0°0′N 91°13′W Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

0°0′N 80°6′W Passing 24 km north of central Quito
Quito
San Francisco de Quito, most often called Quito , is the capital city of Ecuador in northwestern South America. It is located in north-central Ecuador in the Guayllabamba river basin, on the eastern slopes of Pichincha, an active stratovolcano in the Andes mountains...

The Mitad del Mundo is a tract of land owned by the prefecture of the province of Pichincha, Ecuador. It is located in the San Antonio parish of the canton of Quito, north of the center of Quito....

0°0′N 75°32′W Passing 4.3 km north of the border with Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

0°0′N 70°3′W Amazonas
> Roraima
Roraima
Roraima is the northernmost and least populated state of Brazil, located in the Amazon region. It borders the states of Amazonas and Pará, as well as the nations of Venezuela and Guyana. The population is 400,000 and the capital is Boa Vista...

> Amazonas
> Pará
Pará
Pará is a state in the north of Brazil. It borders the Brazilian states of Amapá, Maranhão, Tocantins, Mato Grosso, Amazonas and Roraima. To the northwest it also borders Guyana and Suriname, and to the northeast it borders the Atlantic Ocean. The capital is Belém.Pará is the most populous state...

> Amapá
Amapá
Amapá is one of the states of Brazil, located in the extreme north, bordering French Guiana and Suriname to the north. To the east is the Atlantic Ocean, and to the south and west is the Brazilian state of Pará. Perhaps one of the main features of the state is the River Oiapoque, as it was once...

> Pará - islands in the mouth of the Amazon River
Amazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...

0°0′N 49°20′W Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

Despite its name, no part of Equatorial Guinea
Equatorial Guinea
Equatorial Guinea, officially the Republic of Equatorial Guinea where the capital Malabo is situated.Annobón is the southernmost island of Equatorial Guinea and is situated just south of the equator. Bioko island is the northernmost point of Equatorial Guinea. Between the two islands and to the...

's territory lies on the Equator. However, its island of Annobón
Annobón Province
Annobón , also known as Pagalu or Pigalu, is an island of Equatorial Guinea. It is located in the South Atlantic Ocean at , about 220 miles west of Gabon and south west of São Tomé Island...

is 155 kilometre south of the Equator, and the rest of the country lies to the north.

## Crossing the Equator

Certain navies, such as the Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

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 King Neptune
King Neptune
King Neptune may refer to:* King Neptune , a pig that was used to raise \$19 million in war bonds during World War II* King Neptune, an officiator in a naval Line-crossing ceremony...

, are also held for passengers' entertainment on some civilian ocean liners and cruise ships.

## Exact length of the Equator

In two widely-used geodetic
Geodesy
Geodesy , also named geodetics, a branch of earth sciences, is the scientific discipline that deals with the measurement and representation of the Earth, including its gravitational field, in a three-dimensional time-varying space. Geodesists also study geodynamical phenomena such as crustal...

standards, the Equator is modeled as a circle whose radius is a whole number
Integer
The integers are formed by the natural numbers together with the negatives of the non-zero natural numbers .They are known as Positive and Negative Integers respectively...

of metres. In 1976 the IAU
International Astronomical Union
The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...

standardized this radius as 6378.14 kilometres (3,963 mi), subsequently refined by the IUGG
International Union of Geodesy and Geophysics
The International Union of Geodesy and Geophysics is a non-governmental organisation dedicated to the scientific study of the Earth using geophysical and geodesic techniques. The IUGG was established in 1919. Some areas within its scope are environmental preservation, reduction of the effects of...

to 6378.137 kilometres (3,963 mi) and adopted in WGS-84
World Geodetic System
The World Geodetic System is a standard for use in cartography, geodesy, and navigation. It comprises a standard coordinate frame for the Earth, a standard spheroidal reference surface for raw altitude data, and a gravitational equipotential surface that defines the nominal sea level.The latest...

, though the yet more recent IAU-2000 has retained the old IAU-1976 value. In either case, the length of the Equator is by definition exactly 2π times the given standard, which to the nearest millimeter is 40075.016686 kilometres (24,901.5 mi) in WGS-84 and 40075.035535 kilometres (24,901.5 mi) 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.

The geographical mile
Geographical mile
The geographical mile is a unit of length determined by 1 minute of arc along the Earth's equator. For the 1924 International Spheroid this equalled 1855.4 metres...

is defined as one arc minute of the Equator, and therefore has different values depending on which standard equator is used, namely 1855.3248 metres (6,087 ft) or 1855.3257 metres (6,087 ft) for respectively WGS-84 and IAU-2000, a difference of nearly a millimeter.

The earth is modeled commonly as a sphere flattened 0.336% along its axis. This makes the Equator 0.16% longer than a meridian
Meridian (geography)
A meridian is an imaginary line on the Earth's surface from the North Pole to the South Pole that connects all locations along it with a given longitude. The position of a point along the meridian is given by its latitude. Each meridian is perpendicular to all circles of latitude...

(as a great circle passing through the two poles). The IUGG standard meridian is, to the nearest millimeter, 40007.862917 metres (131,259.4 ft), one arc minute of which is 1852.216 metres (6,076.8 ft), explaining the SI
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

standardization of the nautical mile
Nautical mile
The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...

as 1852 metres (6,076 ft), more than 3 metres (10 ft) short of the geographical mile
Geographical mile
The geographical mile is a unit of length determined by 1 minute of arc along the Earth's equator. For the 1924 International Spheroid this equalled 1855.4 metres...

.

## Climate

The zone of the Equator has a tropical rainforest climate
Tropical rainforest climate
A tropical rainforest climate, also known as an equatorial climate, is a tropical climate usually found along the equator...

, also known as an equatorial climate. Usually, its average annual temperature is around 30 °C (86 °F) during the day and 23 °C (73.4 °F) at night. Rainfall is very high, usually from 2,500 to 3,500 mm per year. Average precipitation days are around 200 per year and average sunshine hours are around 2000 per year.

• 1st parallel north
1st parallel north
The 1st parallel north is a circle of latitude that is 1 degree north of the Earth's equatorial plane. It crosses the Atlantic Ocean, Africa, the Indian Ocean, Southeast Asia, the Pacific Ocean and South America....

• 1st parallel south
1st parallel south
The 1st parallel south is a circle of latitude that is 1 degree south of the Earth's equatorial plane. It crosses the Atlantic Ocean, Africa, the Indian Ocean, Southeast Asia, Australasia, the Pacific Ocean and South America....

• Antarctic Circle
Antarctic Circle
The Antarctic Circle is one of the five major circles of latitude that mark maps of the Earth. For 2011, it is the parallel of latitude that runs south of the Equator.-Description:...

• Arctic Circle
Arctic Circle
The Arctic Circle is one of the five major circles of latitude that mark maps of the Earth. For Epoch 2011, it is the parallel of latitude that runs north of the Equator....

• Coriolis Effect
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

• Intertropical Convergence Zone
Intertropical Convergence Zone
The Intertropical Convergence Zone , known by sailors as The Doldrums, is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together....

• Thermal equator
Thermal equator
The thermal equator is a belt encircling the Earth, defined by the set of locations having the highest mean annual temperature at each longitude around the globe...

• Tropic of Cancer
Tropic of Cancer
The Tropic of Cancer, also referred to as the Northern tropic, is the circle of latitude on the Earth that marks the most northerly position at which the Sun may appear directly overhead at its zenith...

• Tropic of Capricorn
Tropic of Capricorn
The Tropic of Capricorn, or Southern tropic, marks the most southerly latitude on the Earth at which the Sun can be directly overhead. This event occurs at the December solstice, when the southern hemisphere is tilted towards the Sun to its maximum extent.Tropic of Capricorn is one of the five...

• Prime Meridian
Prime Meridian
The Prime Meridian is the meridian at which the longitude is defined to be 0°.The Prime Meridian and its opposite the 180th meridian , which the International Date Line generally follows, form a great circle that divides the Earth into the Eastern and Western Hemispheres.An international...