# Oblate spheroid eccentricity (c<a)

## Description

A spheroid, or ellipsoid of revolution is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. An oblate spheroid is a rotationally symmetric ellipsoid having a polar axis shorter than the diameter of the equatorial circle whose plane bisects it (like a lentil).The oblate spheroid is generated by rotation about the Oz axis of an ellipse with semi-major axis a and semi-minor axis c, therefore e may be identified as the eccentricity.

Related formulas## Variables

e | Eccentricity (dimensionless) |

c | Distance from centre to pole along the symmetry axis (c<a) (dimensionless) |

a | Semi-major axis ( the equatorial radius of the spheroid) (dimensionless) |