Definition:Ellipse/Major Axis/Semi-Major Axis

Definition

Consider an ellipse $K$.

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

In the above diagram, $O V_1$ and $O V_2$ are the semi-major axes of $K$.

Also known as

Some sources do not hyphenate: semimajor axis.

Also see

• Definition:Semi-Minor Axis of Ellipse

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

Linguistic Note

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

Compare basis.

Sources

• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): ellipse
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): ellipse

• Weisstein, Eric W. "Ellipse." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Ellipse.html