Oblateness

Oblate also refers to a member of the Roman Catholic religious order of the Missionary Oblates of Mary Immaculate

An oblate spheroid is an ellipsoid having a shorter axis and two equal longer axes (see the spheroid page for a picture).

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

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

where <math>R_{e}<math> the equatorial radius and <math>R_{p}<math> 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 <math>G<math>, the rotation period <math>T<math> and the density <math>\rho<math>.