physics - Oblate

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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 actually assuming a monastic lifestyle.

An oblate spheroid is ellipsoid having a shorter axis and two equal longer axes.

An oblate spheroid

Oblateness is a measure for a planet that is a spheroid in shape, bulging outward in the center due to its rotation. Effectively the (fictitious) centrifugal force fights against gravity causing the planet to look more like a sphere stretched at the equator.

Mathematically, oblateness may be defined as

$\epsilon = {R_{e}-R_{p} \over R_{e}} \approx {3 \pi \over 2 G T^{2} \rho}$

where $R e$ the equatorial radius and $R p$ is the polar radius. 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 $ρ$ .

Categories: Astronomy