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Encyclopedia > Equator
World map showing the equator in red

## Geodesy of the equator GA_googleFillSlot("encyclopedia_square");

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.
A monument marking the equator at the city of Pontianak, Indonesia.

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. It is the only line of latitude which is also a great circle. The imaginary circle obtained when the Earth's equator is projected onto the sky is called the celestial equator. The 4 main circles of latitude on Earth A circle of latitude is an imaginary east-west circle on the Earth, that connects all locations with a given latitude. ... This article is about rotation as a movement of a physical body. ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... For the Brisbane bus routes known collectively as the Great Circle Line (598 & 599), see the following list of Brisbane Transport routes A great circle on a sphere A great circle is a circle on the surface of a sphere that has the same diameter as the sphere, dividing the... The celestial equator is a great circle on the imaginary celestial sphere, which could be constructed by inflating the Earths equator until it intersects with said sphere. ...

The Sun, in its seasonal movement through the sky, passes directly over the equator twice each year, on the March and September equinoxes. At the equator, the rays of the sun are perpendicular to the surface of the earth on these dates. Sol redirects here. ... This article or section is in need of attention from an expert on the subject. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... The March equinox is the equinox which occurs in the month of March. ... The September equinox is the equinox which occurs in the month of September. ... For other uses, see Equinox (disambiguation). ... Fig. ...

Places on the equator experience the quickest rates of sunrise and sunset in the world. 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). North or south of the equator day length increasingly varies with the seasons. A typical sunrise, in New Zealand A sunrise through clouds over Oakland, California. ... A composite image showing the terminator dividing night from day, running across Europe and Africa. ...

The Earth bulges slightly at the equator. It has an average diameter of 12,750 km, but at the equator the diameter is approximately 43 km greater. This article is about Earth as a planet. ... An equatorial bulge is a planetological term which describes a bulge which a planet may have around its equator, distorting it into an oblate spheroid. ...

Locations near the equator are good sites for spaceports (e.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. (They must be launched to the East to use this effect.) A spaceport is a site for launching spacecraft, by analogy with airport for aircraft. ... The now-decommissioned Ariane 4 launch site The Guiana Space Centre (French: Centre Spatial Guyanais or CSG) is a French spaceport near Kourou in French Guiana. ... Kourou is a town and commune in French Guiana. ...

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. 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 rainy and humid conditions mean that the equatorial climate is not the hottest in the world.[1] A noontime scene from the Philippines on a day when the Sun is almost directly overhead. ... This article or section is in need of attention from an expert on the subject. ... Elevation histogram of the surface of the Earth â€“ approximately 71% of the Earths surface is covered with water. ... Animated map exhibiting the worlds oceanic waters. ...

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. 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. For other uses of Cayambe, see Cayambe (disambiguation page) Cayambe (or VolcÃ¡n Cayambe) is the name of a volcano located in the Cordillera Oriental, a branch of the Ecuadorian Andes. ... The snow line is the point above which, or poleward of which, snow and ice cover the ground throughout the year. ... For other uses, see Snow (disambiguation). ...

## Equatorial countries and territories

The equator traverses the land and/or territorial waters of 14 countries. Starting at west Africa and moving east, these are: For other uses, see Country (disambiguation). ...

## "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. These rituals date back to the Middle Ages, though the current ceremonies are most likely derived from Viking traditions[citation needed]. 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. If the crossing occurs at the Greenwich or Prime Meridian, the sailor is considered to be an "Emerald Shellback".[2] For other uses, see Crossing the Line. ... For other uses, see Viking (disambiguation). ... The 180th meridian is the line of longitude exactly opposite the Prime Meridian. ... Location of the Prime Meridian Image:Prime Meridian. ...

## 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. 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 40,075,035.535 m in IAU-1976 and IAU-2000. IAU redirects here. ... The International Union of Geodesy and Geophysics, or IUGG, is a non-governmental organisation dedicated to the scientific study of the Earth and to the application of the knowledge gained to the needs of society that was established in 1919. ... WGS 84 is the 1984 revision of the World Geodetic System. ... WGS 84 is the 1984 revision of the World Geodetic System. ...

(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 1855.3248 m or 1855.3257 m for respectively WGS-84 and IAU-2000, a difference of nearly a millimeter. The geographical mile is a unit of length determined by 1 minute of arc along the Earths equator, approximately equal to 1855 metres (6087. ...

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). 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. On the earth, a meridian is a north-south line between the North Pole and the South Pole. ... Look up si, Si, SI in Wiktionary, the free dictionary. ... A nautical mile or sea mile is a unit of length. ... The geographical mile is a unit of length determined by 1 minute of arc along the Earths equator, approximately equal to 1855 metres (6087. ...

## 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)
1. ^ (1982) in Rosalind Carreck: The Family Encyclopedia of Natural History. Feltham, England: The Hamlyn Publishing Group Ltd., 190. ISBN 0711202257.
2. ^ List of Unofficial US Navy Certificates

Wikimedia Commons has media related to:
Equator
Zoomable PDF of the map this is based on The Antarctic Circle is one of the five major circles of latitude that mark maps of the Earth. ... For the fast food restaurant chain, see Arctic Circle Restaurants. ... The thunderstorms of the Intertropical Convergence Zone form a line across the eastern Pacific Ocean. ... Location of the Prime Meridian Image:Prime Meridian. ... Climate map showing the 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. ... For the novel by Henry Miller, see Tropic of Cancer (novel). ... World map showing the Tropic of Capricorn For the novel by Henry Miller, see Tropic of Capricorn (novel). ...

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