An equatorial bulge is a difference between the equatorial and polar diameters of a planet, due to the centrifugal force exerted by the rotation about the body's axis. A rotating body tends to form an oblate spheroid rather than a sphere.
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👉 Equatorial bulge in the context of Stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface.
The rotation of a star produces an equatorial bulge due to centrifugal force. As stars are not solid bodies, they can also undergo differential rotation. Thus the equator of the star can rotate at a different angular velocity than the higher latitudes. These differences in the rate of rotation within a star may have a significant role in the generation of a stellar magnetic field.
In this Dossier
Equatorial bulge in the context of Elevation
The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § Vertical datum).The term elevation is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a spacecraft in orbit, and depth is used for points below the surface.
Elevation is not to be confused with the distance from the center of the Earth. Due to the equatorial bulge, the summits of Mount Everest and Chimborazo have, respectively, the largest elevation and the largest geocentric distance.
Equatorial bulge in the context of Geoid
The geoid (/ˈdʒiː.ɔɪd/ JEE-oyd) is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is extended through the continents (such as might be approximated with very narrow hypothetical canals). According to Carl Friedrich Gauss, who first described it, it is the "mathematical figure of the Earth", a smooth but irregular surface whose shape results from the uneven distribution of mass within and on the surface of Earth. It can be known only through extensive gravitational measurements and calculations. Despite being an important concept for almost 200 years in the history of geodesy and geophysics, it has been defined to high precision only since advances in satellite geodesy in the late 20th century.
The geoid is often expressed as a geoid undulation or geoidal height above a given reference ellipsoid, which is a slightly flattened sphere whose equatorial bulge is caused by the planet's rotation. Generally the geoidal height rises where the Earth's material is locally more dense and exerts greater gravitational force than the surrounding areas. The geoid in turn serves as a reference coordinate surface for various vertical coordinates, such as orthometric heights, geopotential heights, and dynamic heights (see Geodesy).
Equatorial bulge in the context of Chimborazo (volcano)
Chimborazo (Spanish: [tʃimboˈɾaso] ) is a stratovolcano in Ecuador and the Cordillera Occidental range of the Andes. Its last known eruption is believed to have occurred around AD 550. Although not the tallest mountain in the Andes or on Earth relative to sea level, its summit is the farthest point on Earth's surface from the Earth's center due to its location along the planet's equatorial bulge. Chimborazo's height from sea level is 6,263 m (20,548 ft), well below that of Mount Everest at 8,849 m (29,031 ft).
Chimborazo is the highest mountain in Ecuador and the 39th-highest peak in the entire Andes. It is a popular destination for mountaineering due to its challenging climbing routes, which involve traversing snow, ice, and rocky terrain.
Equatorial bulge in the context of 45th parallel north
The 45th parallel north is a circle of latitude that is 45 degrees north of Earth's equator. It crosses Europe, Asia, the Pacific Ocean, North America, and the Atlantic Ocean.The 45th parallel north is often called the halfway point between the equator and the North Pole, but the true halfway point is 16.0 km (9.9 mi) north of it (approximately between 45°08'39" and 45°08'40") because Earth is an oblate spheroid; that is, it bulges at the equator and is flattened at the poles.
At this latitude, the sun is visible for 15 hours 37 minutes during the summer solstice, and 8 hours 46 minutes during the winter solstice. The midday Sun stands 21.6° above the southern horizon at the December solstice, 68.4° at the June solstice, and exactly 45.0° at either equinox.