Equatorial bulge

An equatorial bulge is the greater distance from a rotating celestial body's center to its equator than to its poles, caused mainly by rotation.

Centrifugal force: An apparent outward force in a rotating reference frame, directed away from its axis of rotation. In the rotating frame, it counteracts gravity more strongly at the equator than near the poles.
Earth: The third planet from the Sun, with an atmosphere, liquid-water oceans, and a differentiated interior. Earth's equatorial radius is about 21 kilometers greater than its polar radius.
Equatorial radius: The distance from a body's center to its surface in the equatorial plane. It is the radius enlarged by the equatorial bulge.
Earth's gravity field: The spatial variation of gravitational acceleration and potential around Earth. Earth's nonspherical mass distribution makes gravity vary with latitude and altitude.
Hydrostatic equilibrium: A state in which pressure gradients balance body forces within a fluid or deformable body. A fluid planet's shape settles where pressure, gravity, and rotation balance.
Jupiter: The largest planet in the Solar System, a rapidly rotating gas giant. Its rapid rotation gives it one of the Solar System's most pronounced planetary bulges.
Polar radius: The distance from a body's center to its surface along its rotation axis. Comparing it with the equatorial radius measures the bulge.
J2 gravitational coefficient: A dimensionless coefficient describing the leading axisymmetric departure of a body's gravity field from spherical symmetry. It captures the gravitational effect of a planet's equatorial bulge.
Oblate spheroid: A flattened ellipsoid of revolution whose equatorial radius exceeds its polar radius. This geometric shape approximates the form produced by an equatorial bulge.
Saturn: The sixth planet from the Sun, a gas giant with a ring system. Its low average density and rapid rotation produce especially strong flattening.

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