Oblate Spheroid
From OCE Space Simulation
An oblate spheroid is a three-dimensional shape similar to a sphere; however, an oblate spheroid has a shorter polar radius than equatorial radius. Almost all "spherical" celestial bodies are in fact oblate spheroids. In describing planets and other celestial bodies, use the term "oblate spheroid" to describe an object only if the equatorial radius is significantly greater than the polar radius - in general, if the equatorial radius is more than 5% greater than the polar radius, it is a good idea to indicate this.
Dimensions
The equatorial radius is denoted by Er, and the polar radius is denoted by Pr.
