# Eccentricity of an ellipse

## Description

Ellipse is a curve on a plane surrounding two focal points such that a straight line drawn from one of the focal points to any point on the curve and then back to the other focal point has the same length for every point on the curve. Eccentricity denotes how much the ellipse deviates from being circular. The shape of an ellipse (how 'elongated’ it is) is represented by its eccentricity, which for an ellipse can be any number from 0 (the limiting case of a circle) to arbitrarily close to but less than 1.
Analytically, an ellipse can also be defined as the set of points such that the ratio of the distance of each point on the curve from a given point (called a focus or focal point) to the distance from that same point on the curve to a given line (called the directrix) is a constant, called the eccentricity of the ellipse. Related formulas

## Variables

 ϵ Eccentricity (dimensionless) a One-half of the ellipse's major axe (m) b One-half of the ellipse's minor axe (m)