Definition:Ellipse/Major Axis

Definition

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

Definition $1$

The major axis of $K$ is the line segment passing through both $F_1$ and $F_2$ whose endpoints are where it intersects $K$.

Definition $2$

The major axis of $K$ is the diameter of $K$ which has the greatest length.

In the above diagram, $V_1 V_2$ is the major axis of $K$.

Semi-Major Axis

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

Also see

• Equivalence of Definitions of Major Axis of Ellipse
• Major Axis of Ellipse is Axis of Symmetry
• Definition:Minor Axis of Ellipse

• Results about the major axis of an ellipse can be found here.