The equator is the circle of latitude that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, about 40,075 km (24,901 mi) in circumference, halfway between the North and South poles. The term can also be used for any other celestial body that is roughly spherical.
In spatial (3D) geometry, as applied in astronomy, the 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 an 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 and near the equator (on Earth), noontime sunlight appears almost directly overhead (no more than about 23° from the zenith) every day, year-round. Consequently, the equator has a rather stable daytime temperature throughout the year. On the equinoxes (approximately March 20 and September 23) the subsolar point crosses Earth's equator at a shallow angle, sunlight shines perpendicular to Earth's axis of rotation, and all latitudes have nearly a 12-hour day and 12-hour night.
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 'make equal'.
Overview
Right: 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 the two polar circles (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—meaning, 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 a year: on the equinoxes in March and September. To a person on Earth, the Sun appears to travel along the equator (or along the celestial equator) at these times.
Locations 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; its average diameter is 12,742 km (7,918 mi), but the diameter at the equator is about 43 km (27 mi) greater than at the poles.
Sites near the equator, such as the Guiana Space Centre in Kourou, French Guiana, are good locations for spaceports as they have the fastest rotational speed of any latitude, 460 m (1,509 ft)/sec. 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.
Geodesy
Precise location
The precise location of the equator is not truly fixed; the true equatorial plane is perpendicular to the Earth's rotation axis, which drifts about 9 metres (30 ft) during a year.
Geological samples show that the equator significantly changed positions between 48 and 12 million years ago, as sediment deposited by ocean thermal currents at the equator shifted. The deposits by thermal currents are determined by the axis of Earth, which determines solar coverage of Earth's surface. Changes in Earth's axis can also be observed in the geographical layout of volcanic island chains, which are created by shifting hot spots under Earth's crust as the axis and crust move. This is consistent with the Indian tectonic plate colliding with the Eurasian tectonic plate, which is causing the Himalayan uplift.
Exact length
The International Association of Geodesy (IAG) and the International Astronomical Union (IAU) use an equatorial radius of 6,378.1366 km (3,963.1903 mi) (codified as the IAU 2009 value). This equatorial radius is also in the 2003 and 2010 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 km (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 km (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 km (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 1,855.3248 metres (6,087.024 ft), while by IAU-2000, it is 1,855.3257 metres (6,087.027 ft). This is a difference of less than one millimetre (0.039 in) over the total distance (approximately 1.86 kilometres or 1.16 miles).
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, 40,007.862917 kilometres (24,859.733480 mi), one arc-minute of which is 1,852.216 metres (6,076.82 ft), explaining the SI standardization of the nautical mile as 1,852 metres (6,076 ft), more than 3 metres (9.8 ft) less than the geographical mile.
The sea-level surface of 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 300 metres (1,000 ft) greater than its diameter ninety degrees away.[citation needed]
Equatorial countries and territories
The equator passes through the land of eleven sovereign states. Indonesia is the country straddling the greatest length of the equatorial line across both land and sea. Starting at the Prime Meridian and heading eastwards, the equator passes through:
| Coordinates | Country or water body | Notes |
|---|---|---|
| 0°N 0°E / 0°N 0°E | Atlantic Ocean | Gulf of Guinea, "Null Island" |
| 0°0′N 6°31′E / 0.000°N 6.517°E |  São Tomé and Príncipe | Passing through Pestana Equador resort on the Ilhéu das Rolas |
| 0°0′N 9°21′E / 0.000°N 9.350°E |  Gabon | Passing 8.9 km (5.5 mi) south of Ayem, 10.6 km (6.6 mi) north of Mayene, Booue |
| 0°0′N 13°57′E / 0.000°N 13.950°E |  Congo | Passing through the town of Makoua. |
| 0°0′N 17°45′E / 0.000°N 17.750°E |  DR Congo | Passing 9 km (5.6 mi) south of central Butembo |
| 0°0′N 29°44′E / 0.000°N 29.733°E |  Uganda | Passing 32 km (20 mi) south of central Kampala |
| 0°0′N 32°13′E / 0.000°N 32.217°E | Lake Victoria | Passing through some islands of Uganda in Mukono District and Namayingo District |
| 0°0′N 34°0′E / 0.000°N 34.000°E |  Kenya | Passing 6 km (3.7 mi) north of central Kisumu. Passes through the highest mountain in Kenya i.e Mount Kenya |
| 0°0′N 41°0′E / 0.000°N 41.000°E |  Somalia | Passing south of Jamame |
| 0°0′N 42°53′E / 0.000°N 42.883°E | Indian Ocean | Passing between Huvadhu Atoll and Fuvahmulah of  Maldives |
| 0°0′N 98°13′E / 0.000°N 98.217°E |  Indonesia | North Sumatra (Batu Islands), West Sumatra (West Pasaman, Pasaman and Lima Puluh Kota Regency), Riau (Kampar, Pelalawan and Indragiri Hilir Regency), and Lingga Regency of Riau Islands |
| 0°0′N 104°35′E / 0.000°N 104.583°E | South China Sea | |
| 0°0′N 109°10′E / 0.000°N 109.167°E | Indonesia | Bornean provinces of West Kalimantan (passing through province capital Pontianak), Central Kalimantan, and East Kalimantan |
| 0°0′N 117°31′E / 0.000°N 117.517°E | Makassar Strait | |
| 0°0′N 119°40′E / 0.000°N 119.667°E | Indonesia | Donggala & Parigi Moutong Regency, Central Sulawesi (Celebes) |
| 0°0′N 120°6′E / 0.000°N 120.100°E | Gulf of Tomini | |
| 0°0′N 123°22′E / 0.000°N 123.367°E | Molucca Sea | |
| 0°0′N 127°25′E / 0.000°N 127.417°E | Indonesia | Kayoa and Halmahera islands, North Maluku |
| 0°0′N 127°53′E / 0.000°N 127.883°E | Halmahera Sea | |
| 0°0′N 129°21′E / 0.000°N 129.350°E | Indonesia | Gebe and Kawe islands, North Maluku, Southwest Papua |
| 0°0′N 130°11′E / 0.000°N 130.183°E | Pacific Ocean | Passing between Aranuka and Nonouti atolls,  Kiribati (at 0°0′N 173°45′E / 0.000°N 173.750°E)Also passing just south of Baker Island, and just north of Jarvis Island,  United States Minor Outlying Islands |
| 0°0′N 91°35′W / 0.000°N 91.583°W |  Ecuador | Isabela Island in the Galápagos Islands |
| 0°0′N 91°13′W / 0.000°N 91.217°W | Pacific Ocean | |
| 0°0′N 80°7′W / 0.000°N 80.117°W | Ecuador | Passing 24 km (15 mi) north of central Quito, near Mitad del Mundo, and precisely at the location of Catequilla, a pre-Columbian ruin. |
| 0°0′N 75°35′W / 0.000°N 75.583°W |  Colombia | Passing 4.3 km (2.7 mi) north of the border with Peru |
| 0°0′N 70°3′W / 0.000°N 70.050°W |  Brazil | 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) |
| 0°0′N 49°21′W / 0.000°N 49.350°W | Atlantic Ocean | At the on the mouth of the Amazon River |
The equator also passes through the territorial seas of three countries: Maldives (south of Gaafu Dhaalu Atoll), Kiribati (south of Buariki Island), and the United States (south of Baker Island).
Despite its name, no part of Equatorial Guinea lies on the equator. However, its island of Annobón is 155 km (96 mi) south of the equator, and the rest of the country lies to the north. France, Norway (Bouvet Island), and the United Kingdom are the other three Northern Hemisphere-based countries which have territories in the Southern Hemisphere.
Equatorial seasons and climate
Diagram of the seasons, showing the situation at the December solstice. Regardless of the time of day (i.e. Earth's rotation on its axis), the North Pole will be dark, and the South Pole will be illuminated; see also polar night. In addition to the density of incident light, the dissipation of light in atmosphere is greater when it falls at a shallow angle.
Seasons result from the tilt of Earth's axis away from a line perpendicular 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, 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 Earth.
Near the equator, this means the variation in the strength of solar radiation is different relative to the time of year than it is at higher latitudes: maximum solar radiation is received during the equinoxes, when a place at the equator is under the subsolar point at high noon, and the intermediate seasons of spring and autumn occur at higher latitudes; and the minimum occurs during both solstices, when either pole is tilted towards or away from the sun, resulting in either summer or winter in both hemispheres. This also results in a corresponding movement of the equator away from the subsolar point, which is then situated over or near the relevant tropic circle. Nevertheless, temperatures are high year-round due to the Earth's axial tilt of 23.5° not being enough to create a low minimum midday declination to sufficiently weaken the Sun's rays even during the solstices. High year-round temperatures extend to about 25° north or south of the equator, although the moderate seasonal temperature difference is defined by the opposing solstices (as it is at higher latitudes) near the poleward limits of this range.
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 ocean 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 31 °C (88 °F) during the afternoon and 23 °C (73 °F) around sunrise. Rainfall is very high away from cold ocean current upwelling zones, from 2,500 to 3,500 mm (100 to 140 in) 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 4,690 metres (15,387 ft), at 0°0′0″N 77°59′31″W / 0.00000°N 77.99194°W, found on the southern slopes of Volcán Cayambe [summit 5,790 metres (18,996 ft)] 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 1,000 metres (3,300 ft) lower than on Mount Everest and as much as 2,000 metres (6,600 ft) lower than the highest snow line in the world, near the Tropic of Capricorn on Llullaillaco.
| 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) | 54.1 (2.13) | 6.6 (0.26) | 13.7 (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),Hong Kong Observatory | |||||||||||||
| 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) | |||||||||||||
| Climate data for Macapá, Brazil in South America | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
| Mean daily maximum °C (°F) | 29.7 (85.5) | 29.2 (84.6) | 29.3 (84.7) | 29.5 (85.1) | 30.0 (86.0) | 30.3 (86.5) | 30.6 (87.1) | 31.5 (88.7) | 32.1 (89.8) | 32.6 (90.7) | 32.3 (90.1) | 31.4 (88.5) | 30.71 (87.28) |
| Daily mean °C (°F) | 26.5 (79.7) | 26.2 (79.2) | 26.3 (79.3) | 26.4 (79.5) | 26.8 (80.2) | 26.8 (80.2) | 26.8 (80.2) | 27.4 (81.3) | 27.8 (82.0) | 28.1 (82.6) | 27.9 (82.2) | 27.4 (81.3) | 27.03 (80.65) |
| Mean daily minimum °C (°F) | 23.0 (73.4) | 23.1 (73.6) | 23.2 (73.8) | 23.5 (74.3) | 23.5 (74.3) | 23.2 (73.8) | 22.9 (73.2) | 23.3 (73.9) | 23.4 (74.1) | 23.5 (74.3) | 23.5 (74.3) | 23.4 (74.1) | 23.29 (73.92) |
| Average rainfall mm (inches) | 299.6 (11.80) | 347.0 (13.66) | 407.2 (16.03) | 384.3 (15.13) | 351.5 (13.84) | 220.1 (8.67) | 184.8 (7.28) | 98.0 (3.86) | 42.6 (1.68) | 35.5 (1.40) | 58.4 (2.30) | 142.5 (5.61) | 2,571.5 (101.26) |
| Average rainy days (≥ 0.1 mm) | 23 | 22 | 24 | 24 | 25 | 22 | 19 | 13 | 6 | 5 | 6 | 14 | 203 |
| Mean monthly sunshine hours | 148.8 | 113.1 | 108.5 | 114.0 | 151.9 | 189.0 | 226.3 | 272.8 | 273.0 | 282.1 | 252.0 | 204.6 | 2,336.1 |
| Source: World Meteorological Organization (UN),Hong Kong Observatory | |||||||||||||
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] Milder line-crossing ceremonies, typically featuring King Neptune, are also held for passengers' entertainment on some civilian ocean liners and cruise ships.[citation needed]
See also
- 1st parallel north
- 1st parallel south
- Bogota Declaration
- Coriolis force
- Intertropical Convergence Zone
- Planetary equator
- Prime meridian
- Thermal equator
References
- "Equator". National Geographic - Education. 6 September 2011. Retrieved 9 March 2021.
- Kher, Aparna. "Equinox: Almost Equal Day and Night". timeanddate.com. Retrieved 5 November 2021.
- "Definition of equator". Oxford Dictionaries. Archived from the original on May 23, 2018. Retrieved 5 May 2018.
- William Barnaby Faherty; Charles D. Benson (1978). "Moonport: A History of Apollo Launch Facilities and Operations". NASA History Series. p. Chapter 1.2: A Saturn Launch Site. NASA Special Publication-4204. Archived from the original on 15 September 2018. Retrieved 8 May 2019.
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 m/s (1,510 ft/s)) 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.
- Funk, Anna (Nov 26, 2018). "Millions of Years Ago, the Poles Moved — And It Could Have Triggered an Ice Age". Discover Magazine. Archived from the original on Sep 24, 2023.
- Luzum, Brian; Capitaine, Nicole; Fienga, Agnès; Folkner, William; Fukushima, Toshio; Hilton, James; Hohenkerk, Catherine; Krasinsky, George; Petit, Gérard; Pitjeva, Elena; Soffel, Michael; Wallace, Patrick (2011). "The IAU 2009 system of astronomical constants: the report of the IAU working group on numerical standards for Fundamental Astronomy" (PDF). Celest Mech Dyn Astr. 110 (4): 293–304. Bibcode:2011CeMDA.110..293L. doi:10.1007/s10569-011-9352-4. S2CID 122755461. Archived (PDF) from the original on Aug 1, 2023.
- "General definitions and numerical standards" (PDF). IERS Technical Note 36. Archived from the original (PDF) on 18 December 2018.
- Instituto Geográfico Militar de Ecuador (24 January 2005). "Memoria Técnica de la Determinación de la Latitud Cero" (in Spanish).
- "Weather Information for Libreville". World Weather Information Service. World Meteorological Organization.
- "Climatological Normals of Libreville". Hong Kong Observatory. Archived from the original on 26 October 2019.
- "Weather Information for Pontianak". World Weather Information Service. World Meteorological Organization.
- "Weather Information for Macapa". World Weather Information Service. World Meteorological Organization.
- "Climatological Normals of Macapa". Hong Kong Observatory. Archived from the original on 26 October 2019.
Sources
- Moritz, H (September 1980). "Geodetic Reference System 1980". Bulletin Géodésique. 54 (3). Berlin: Springer-Verlag: 395–405. Bibcode:1980BGeod..54..395M. doi:10.1007/BF02521480. S2CID 198209711. (IUGG/WGS-84 data)
- Taff, Laurence G (1981). Computational Spherical Astronomy. New York: Wiley. ISBN 0-471-06257-X. OCLC 6532537. (IAU data)
The equator is the circle of latitude that divides Earth into the Northern and Southern hemispheres It is an imaginary line located at 0 degrees latitude about 40 075 km 24 901 mi in circumference halfway between the North and South poles The term can also be used for any other celestial body that is roughly spherical 0 class notpageimage The equator on a map of Earth Countries and territories that are intersected by the equator red or the Prime Meridian blue which intersect at Null Island The Equator during the boreal winter spanning from December to March In spatial 3D geometry as applied in astronomy the 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 an 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 and near the equator on Earth noontime sunlight appears almost directly overhead no more than about 23 from the zenith every day year round Consequently the equator has a rather stable daytime temperature throughout the year On the equinoxes approximately March 20 and September 23 the subsolar point crosses Earth s equator at a shallow angle sunlight shines perpendicular to Earth s axis of rotation and all latitudes have nearly a 12 hour day and 12 hour night EtymologyThe 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 make equal OverviewLeft A monument marking the equator near the city of Pontianak Indonesia Right 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 the two polar circles 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 meaning 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 a year on the equinoxes in March and September To a person on Earth the Sun appears to travel along the equator or along the celestial equator at these times The equator marked as it crosses Ilheu das Rolas in Sao Tome and PrincipeThe Marco Zero monument marking the equator in Macapa Brazil Locations 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 its average diameter is 12 742 km 7 918 mi but the diameter at the equator is about 43 km 27 mi greater than at the poles Sites near the equator such as the Guiana Space Centre in Kourou French Guiana are good locations for spaceports as they have the fastest rotational speed of any latitude 460 m 1 509 ft sec 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 GeodesyPrecise location The precise location of the equator is not truly fixed the true equatorial plane is perpendicular to the Earth s rotation axis which drifts about 9 metres 30 ft during a year Geological samples show that the equator significantly changed positions between 48 and 12 million years ago as sediment deposited by ocean thermal currents at the equator shifted The deposits by thermal currents are determined by the axis of Earth which determines solar coverage of Earth s surface Changes in Earth s axis can also be observed in the geographical layout of volcanic island chains which are created by shifting hot spots under Earth s crust as the axis and crust move This is consistent with the Indian tectonic plate colliding with the Eurasian tectonic plate which is causing the Himalayan uplift Exact length The International Association of Geodesy IAG and the International Astronomical Union IAU use an equatorial radius of 6 378 1366 km 3 963 1903 mi codified as the IAU 2009 value This equatorial radius is also in the 2003 and 2010 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 2p times the radius namely 40 075 0142 km 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 km 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 km 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 1 855 3248 metres 6 087 024 ft while by IAU 2000 it is 1 855 3257 metres 6 087 027 ft This is a difference of less than one millimetre 0 039 in over the total distance approximately 1 86 kilometres or 1 16 miles 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 40 007 862917 kilometres 24 859 733480 mi one arc minute of which is 1 852 216 metres 6 076 82 ft explaining the SI standardization of the nautical mile as 1 852 metres 6 076 ft more than 3 metres 9 8 ft less than the geographical mile The sea level surface of 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 300 metres 1 000 ft greater than its diameter ninety degrees away citation needed Equatorial countries and territoriesMap all coordinates using OpenStreetMap Download coordinates as KML GPX all coordinates GPX primary coordinates GPX secondary coordinates GPS reading taken on the equator close to the Quitsato Sundial in Cayambe EcuadorSign on the equator in San Antonio de Pichincha Ecuador The N1 road crossing the Equator in Gabon north of Bifoun The equator passes through the land of eleven sovereign states Indonesia is the country straddling the greatest length of the equatorial line across both land and sea Starting at the Prime Meridian and heading eastwards the equator passes through Coordinates Country or water body Notes0 N 0 E 0 N 0 E 0 0 Prime Meridian Atlantic Ocean Gulf of Guinea Null Island 0 0 N 6 31 E 0 000 N 6 517 E 0 000 6 517 Sao Tome and Principe Sao Tome and Principe Passing through Pestana Equador resort on the Ilheu das Rolas0 0 N 9 21 E 0 000 N 9 350 E 0 000 9 350 Gabon Gabon Passing 8 9 km 5 5 mi south of Ayem 10 6 km 6 6 mi north of Mayene Booue0 0 N 13 57 E 0 000 N 13 950 E 0 000 13 950 Republic of the Congo Congo Passing through the town of Makoua 0 0 N 17 45 E 0 000 N 17 750 E 0 000 17 750 Democratic Republic of the Congo DR Congo Passing 9 km 5 6 mi south of central Butembo0 0 N 29 44 E 0 000 N 29 733 E 0 000 29 733 Uganda Uganda Passing 32 km 20 mi south of central Kampala0 0 N 32 13 E 0 000 N 32 217 E 0 000 32 217 Lake Victoria Lake Victoria Passing through some islands of Uganda in Mukono District and Namayingo District0 0 N 34 0 E 0 000 N 34 000 E 0 000 34 000 Kenya Kenya Passing 6 km 3 7 mi north of central Kisumu Passes through the highest mountain in Kenya i e Mount Kenya0 0 N 41 0 E 0 000 N 41 000 E 0 000 41 000 Somalia Somalia Passing south of Jamame0 0 N 42 53 E 0 000 N 42 883 E 0 000 42 883 Indian Ocean Indian Ocean Passing between Huvadhu Atoll and Fuvahmulah of Maldives0 0 N 98 13 E 0 000 N 98 217 E 0 000 98 217 Indonesia Indonesia North Sumatra Batu Islands West Sumatra West Pasaman Pasaman and Lima Puluh Kota Regency Riau Kampar Pelalawan and Indragiri Hilir Regency and Lingga Regency of Riau Islands0 0 N 104 35 E 0 000 N 104 583 E 0 000 104 583 South China Sea South China Sea0 0 N 109 10 E 0 000 N 109 167 E 0 000 109 167 Indonesia Indonesia Bornean provinces of West Kalimantan passing through province capital Pontianak Central Kalimantan and East Kalimantan0 0 N 117 31 E 0 000 N 117 517 E 0 000 117 517 Makassar Strait Makassar Strait0 0 N 119 40 E 0 000 N 119 667 E 0 000 119 667 Indonesia Indonesia Donggala amp Parigi Moutong Regency Central Sulawesi Celebes 0 0 N 120 6 E 0 000 N 120 100 E 0 000 120 100 Gulf of Tomini Gulf of Tomini0 0 N 123 22 E 0 000 N 123 367 E 0 000 123 367 Molucca Sea Molucca Sea0 0 N 127 25 E 0 000 N 127 417 E 0 000 127 417 Indonesia Indonesia Kayoa and Halmahera islands North Maluku0 0 N 127 53 E 0 000 N 127 883 E 0 000 127 883 Halmahera Sea Halmahera Sea0 0 N 129 21 E 0 000 N 129 350 E 0 000 129 350 Indonesia Indonesia Gebe and Kawe islands North Maluku Southwest Papua0 0 N 130 11 E 0 000 N 130 183 E 0 000 130 183 Pacific Ocean Pacific Ocean Passing between Aranuka and Nonouti atolls Kiribati at 0 0 N 173 45 E 0 000 N 173 750 E 0 000 173 750 Also passing just south of Baker Island and just north of Jarvis Island United States Minor Outlying Islands0 0 N 91 35 W 0 000 N 91 583 W 0 000 91 583 Ecuador Ecuador Isabela Island in the Galapagos Islands0 0 N 91 13 W 0 000 N 91 217 W 0 000 91 217 Pacific Ocean Pacific Ocean0 0 N 80 7 W 0 000 N 80 117 W 0 000 80 117 Ecuador Ecuador Passing 24 km 15 mi north of central Quito near Mitad del Mundo and precisely at the location of Catequilla a pre Columbian ruin 0 0 N 75 35 W 0 000 N 75 583 W 0 000 75 583 Colombia Colombia Passing 4 3 km 2 7 mi north of the border with Peru0 0 N 70 3 W 0 000 N 70 050 W 0 000 70 050 Brazil Brazil Amazonas Roraima Para Amapa passing slightly south of the city center of the state capital Macapa and precisely at the Marco Zero monument and the Avenue Equatorial 0 0 N 49 21 W 0 000 N 49 350 W 0 000 49 350 Atlantic Ocean Atlantic Ocean At the on the mouth of the Amazon River The equator also passes through the territorial seas of three countries Maldives south of Gaafu Dhaalu Atoll Kiribati south of Buariki Island and the United States south of Baker Island Despite its name no part of Equatorial Guinea lies on the equator However its island of Annobon is 155 km 96 mi south of the equator and the rest of the country lies to the north France Norway Bouvet Island and the United Kingdom are the other three Northern Hemisphere based countries which have territories in the Southern Hemisphere Equatorial seasons and climateDiagram of the seasons showing the situation at the December solstice Regardless of the time of day i e Earth s rotation on its axis the North Pole will be dark and the South Pole will be illuminated see also polar night In addition to the density of incident light the dissipation of light in atmosphere is greater when it falls at a shallow angle Seasons result from the tilt of Earth s axis away from a line perpendicular 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 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 Earth Near the equator this means the variation in the strength of solar radiation is different relative to the time of year than it is at higher latitudes maximum solar radiation is received during the equinoxes when a place at the equator is under the subsolar point at high noon and the intermediate seasons of spring and autumn occur at higher latitudes and the minimum occurs during both solstices when either pole is tilted towards or away from the sun resulting in either summer or winter in both hemispheres This also results in a corresponding movement of the equator away from the subsolar point which is then situated over or near the relevant tropic circle Nevertheless temperatures are high year round due to the Earth s axial tilt of 23 5 not being enough to create a low minimum midday declination to sufficiently weaken the Sun s rays even during the solstices High year round temperatures extend to about 25 north or south of the equator although the moderate seasonal temperature difference is defined by the opposing solstices as it is at higher latitudes near the poleward limits of this range 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 ocean 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 31 C 88 F during the afternoon and 23 C 73 F around sunrise Rainfall is very high away from cold ocean current upwelling zones from 2 500 to 3 500 mm 100 to 140 in 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 4 690 metres 15 387 ft at 0 0 0 N 77 59 31 W 0 00000 N 77 99194 W 0 00000 77 99194 highest point on the equator found on the southern slopes of Volcan Cayambe summit 5 790 metres 18 996 ft 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 1 000 metres 3 300 ft lower than on Mount Everest and as much as 2 000 metres 6 600 ft lower than the highest snow line in the world near the Tropic of Capricorn on Llullaillaco Climate data for Libreville Gabon in AfricaMonth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec YearMean 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 1 2 13 6 6 0 26 13 7 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 4Mean 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 9Source World Meteorological Organization UN Hong Kong Observatory Climate data for Pontianak Indonesia in AsiaMonth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec YearMean 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 238Source World Meteorological Organization UN Climate data for Macapa Brazil in South AmericaMonth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec YearMean daily maximum C F 29 7 85 5 29 2 84 6 29 3 84 7 29 5 85 1 30 0 86 0 30 3 86 5 30 6 87 1 31 5 88 7 32 1 89 8 32 6 90 7 32 3 90 1 31 4 88 5 30 71 87 28 Daily mean C F 26 5 79 7 26 2 79 2 26 3 79 3 26 4 79 5 26 8 80 2 26 8 80 2 26 8 80 2 27 4 81 3 27 8 82 0 28 1 82 6 27 9 82 2 27 4 81 3 27 03 80 65 Mean daily minimum C F 23 0 73 4 23 1 73 6 23 2 73 8 23 5 74 3 23 5 74 3 23 2 73 8 22 9 73 2 23 3 73 9 23 4 74 1 23 5 74 3 23 5 74 3 23 4 74 1 23 29 73 92 Average rainfall mm inches 299 6 11 80 347 0 13 66 407 2 16 03 384 3 15 13 351 5 13 84 220 1 8 67 184 8 7 28 98 0 3 86 42 6 1 68 35 5 1 40 58 4 2 30 142 5 5 61 2 571 5 101 26 Average rainy days 0 1 mm 23 22 24 24 25 22 19 13 6 5 6 14 203Mean monthly sunshine hours 148 8 113 1 108 5 114 0 151 9 189 0 226 3 272 8 273 0 282 1 252 0 204 6 2 336 1Source World Meteorological Organization UN Hong Kong ObservatoryLine crossing ceremoniesThere 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 Milder line crossing ceremonies typically featuring King Neptune are also held for passengers entertainment on some civilian ocean liners and cruise ships citation needed See alsoGeography portal1st parallel north 1st parallel south Bogota Declaration Coriolis force Intertropical Convergence Zone Planetary equator Prime meridian Thermal equatorReferences Equator National Geographic Education 6 September 2011 Retrieved 9 March 2021 Kher Aparna Equinox Almost Equal Day and Night timeanddate com Retrieved 5 November 2021 Definition of equator Oxford Dictionaries Archived from the original on May 23 2018 Retrieved 5 May 2018 William Barnaby Faherty Charles D Benson 1978 Moonport A History of Apollo Launch Facilities and Operations NASA History Series p Chapter 1 2 A Saturn Launch Site NASA Special Publication 4204 Archived from the original on 15 September 2018 Retrieved 8 May 2019 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 m s 1 510 ft s 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 Funk Anna Nov 26 2018 Millions of Years Ago the Poles Moved And It Could Have Triggered an Ice Age Discover Magazine Archived from the original on Sep 24 2023 Luzum Brian Capitaine Nicole Fienga Agnes Folkner William Fukushima Toshio Hilton James Hohenkerk Catherine Krasinsky George Petit Gerard Pitjeva Elena Soffel Michael Wallace Patrick 2011 The IAU 2009 system of astronomical constants the report of the IAU working group on numerical standards for Fundamental Astronomy PDF Celest Mech Dyn Astr 110 4 293 304 Bibcode 2011CeMDA 110 293L doi 10 1007 s10569 011 9352 4 S2CID 122755461 Archived PDF from the original on Aug 1 2023 General definitions and numerical standards PDF IERS Technical Note 36 Archived from the original PDF on 18 December 2018 Instituto Geografico Militar de Ecuador 24 January 2005 Memoria Tecnica de la Determinacion de la Latitud Cero in Spanish Weather Information for Libreville World Weather Information Service World Meteorological Organization Climatological Normals of Libreville Hong Kong Observatory Archived from the original on 26 October 2019 Weather Information for Pontianak World Weather Information Service World Meteorological Organization Weather Information for Macapa World Weather Information Service World Meteorological Organization Climatological Normals of Macapa Hong Kong Observatory Archived from the original on 26 October 2019 SourcesWikimedia Commons has media related to Equator Moritz H September 1980 Geodetic Reference System 1980 Bulletin Geodesique 54 3 Berlin Springer Verlag 395 405 Bibcode 1980BGeod 54 395M doi 10 1007 BF02521480 S2CID 198209711 IUGG WGS 84 data Taff Laurence G 1981 Computational Spherical Astronomy New York Wiley ISBN 0 471 06257 X OCLC 6532537 IAU data
