# Definition:Ellipse/Minor Axis

## Definition

Consider an ellipse $K$ whose foci are $F_1$ and $F_2$.

The minor axis of $K$ is the line segment through the center of $K$ perpendicular to the major axis of $K$ such that its endpoints are the points of intersection with $K$.

In the above diagram, $C_1 C_2$ is the minor axis of $K$.

### Semi-Minor Axis

A semi-minor axis of $K$ is either half of the minor axis of $K$ from its midpoint to its endpoint.

## Linguistic Note

The plural of axis is axes, which is pronounced ax-eez not ax-iz.

Compare basis.