# What is an ellipse?

##### 1 Answer

#### Explanation:

**Ellipse Definition**: On a plane, **ellipse** is defined as follows - If two special points (called the foci) are picked on a plane and if we collect all the points around those foci such that the sum of the distances between any point in that collection and the two foci are a constant, then the locus of all these points form a curve called Ellipse.

Though this definition is for ellipse as a plane curve, this definition can be extended to define ellipse on non-planar surfaces, like for example on Earth.

Ellipses are symmetric about exactly two axes that are perpendicular to each other. If we align those two axes along the two cartesian axes

**Cartesian Equation of an Ellipse**:

Here **semi-major** axis and **semi-minor** axis.

Ellipses are characterised by a parameter called **eccentricity** (

A **circle** is a special ellipse with eccentricity zero (

If one of the focus is placed at the coordinate origin and measure the angle (