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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. The Earth has an equatorial bulge of 42.72 km (26.5 miles) due to its rotation. That is, its diameter measured across the equatorial plane (12756.28 km, 7,927 miles) is 42.72 km more than that measured between the poles (12713.56 km, 7,900 miles). Planetary science, also known as planetology or planetary astronomy, is the science of planets and the solar system, and incorporates an interdisciplinary approach drawing from diverse sciences. ...
The equator is an imaginary circle drawn around a planet (or other astronomical object) at a distance halfway between the poles. ...
Oblate also refers to a member of the Roman Catholic religious order of the Missionary Oblates of Mary Immaculate, or in some cases to a lay or religious person who has officially associated himself (or herself) with a monastic community such as the Benedictines for reasons of personal enrichment without...
Earth is the third planet from the Sun. ...
To help compare different orders of magnitude this page lists lengths between 10 and 100 km (104 to 105 m). ...
The equilibrium as a balance of energies
Gravity tends to contract celestial bodies into a perfect sphere, the shape where all the mass is as close to the center of gravity as possible. However given the rotation there is a corresponding equatorial bulge. The common measure of this distortion from spherical shape is called the flattening (or sometimes ellipticity or oblateness), and can depend on a variety of factors including the angular velocity, density, and elasticity. Gravity is a force of attraction that acts between bodies that have mass. ...
A sphere is a perfectly symmetrical geometrical object. ...
Rotation of a plane, seen as the rotation of the terrain relative to the plane (exposure time 1. ...
The flattening, ellipticity, or oblateness of an oblate spheroid is the relative difference between its equatorial radius a and its polar radius b: The flattening of the Earth is 1:298. ...
Angular velocity describes the speed of rotation. ...
Density (symbol: Ï - Greek: rho) is a measure of mass per unit of volume. ...
Elasticity has meanings in two different fields: In physics and mechanical engineering, the theory of elasticity describes how a solid object moves and deforms in response to external stress. ...
Perfect spherical shape is the shape of least gravitational potential energy, so the oblate shape of rotating bodies corresponds to a higher gravitational potential energy. For any rotating planet, relaxing to the state of a perfect sphere is not available. Potential energy (U, or Ep), a kind of scalar potential, is energy by virtue of matter being able to move to a lower-energy state, releasing energy in some form. ...
To get a feel for the type of equilibrium that is involved, imagine someone seated in a swivel chair, with weights in their hands, to whom a rotating motion of the chair is imparted. If the person in the chair pulls the weights towards them, they are doing work and their rotation rate increases. As they pull the weights closer and closer, the force required for yet more contraction keeps increasing.
Something analogous to this occurs in planet formation. Matter first coalesces into a slowly rotating disk-shaped distribution, and collisions and friction convert much kinetic energy to heat, which allows the disk to self-gravitate into a very oblate spheroid.
As long as the proto-planet is still too oblate to be in equilibrium, the release of gravitational potential energy on contraction keeps driving the increase in rotational kinetic energy. As the contraction proceeds the rotation rate keeps going up, hence the required force for further contraction keeps going up. There is a point where the increase of rotational kinetic energy on further contraction would be larger than the release of gravitational potential energy. The contraction process can only proceed up to that point, so it halts there.
As long as there is no equilibrium there can be violent convection, and as long as there is violent convection friction can convert kinetic energy to heat, draining rotational kinetic energy from the system. When the equilibrium state has been reached then large scale conversion of kinetic energy to heat ceases. In that sense the equilibrium state is the lowest state of energy that can be reached.
Strictly speaking the Earth's rate of rotation is still slowing down, there is still some convection (this convection drives the process of plate tectonics), but this dissipation of rotational kinetic energy is very small as compared to when the Earth formed. Plate tectonics (from the Greek word for one who constructs and destroys, τεκτων, tekton) is a theory of geology developed to explain the phenomenon of continental drift and is currently the theory accepted by the vast majority of scientists working in this area. ...
A wave that loses amplitude is said to dissipate. ...
Differences in gravitational acceleration Because of a planet's rotation around its own axis, the gravitational acceleration is less at the equator than at the poles. In the 17th century, following the invention of the pendulum clock, French scientists found that clocks sent to French Guiana, on the northern coast of South America, ran slower than their exact counterparts in Paris. However, measurements of the acceleration due to gravity at the equator must also take into account the planet's rotation. Any object that is stationary with respect to the surface of the Earth is in actual fact following a circular trajectory, circumnavigating the Earth's axis. Pulling an object into such a circular trajectory requires a force. Providing this acceleration goes at the expense of gravitational acceleration. (16th century - 17th century - 18th century - more centuries) As a means of recording the passage of time, the 17th century was that century which lasted from 1601-1700. ...
A pendulum clock uses a pendulum as its time base. ...
South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ...
At the poles, the gravitational acceleration is 9.8322 m/s2. At the equator, the effective gravitational acceleration is 9.7805 m/s2. The true gravitational acceleration at the equator, which can only be inferred, not measured, is 9.8144 m/s2.
The difference between the gravitational acceleration at the poles and the true gravitational acceleration at the equator is due to the fact that the Earth is not spherical in shape. Objects at the equator are about 21 kilometers further away from the center of mass of the Earth, whichs corresponds to a smaller gravitational acceleration.
In summary, there are two contributions to the fact that the effective gravitational acceleration less strong at the equator than at the poles. About 65 percent of the difference is contributed by the fact that objects circumnavigate the Earth's axis, and about 35 percent is due to the non-spherical shape of the Earth.
Satellite orbits The fact that the Earth's gravitational field slightly deviates from being spherically symmetrical also affects the orbits of satellites and changes their orbits away from pure ellipses. This is especially important in the case of the trajectories of GPS-satellites. A satellite is any object that orbits another object (which is known as its primary). ...
The ellipse and some of its mathematical properties. ...
Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...
Other celestial bodies The planet with the largest known equatorial bulge (11808 km, 7337 miles) is Saturn. Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ...
Many rotating astronomical bodies other than planets also exhibit equatorial bulges.
Mathematical expression Mathematically, for flattening we have where a is the equatorial radius, b is the polar radius and b:a is the aspect ratio. The approximation is valid in the case of a fluid planet of uniform density; it is a function of the Newtonian constant of gravitation G, the rotation period T and the density ρ. The equator is an imaginary circle drawn around a planet (or other astronomical object) at a distance halfway between the poles. ...
For other uses of the word pole, see Pole (disambiguation). ...
The aspect ratio of a two-dimensional shape is the ratio of its longest dimension to its shortest dimension. ...
Density (symbol: Ï - Greek: rho) is a measure of mass per unit of volume. ...
According to the law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. ...
In astronomy, a rotation period is the time an astronomical object takes to complete one revolution around its rotation axis. ...
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