# Definition:Right Circular Cone/Opening Angle

< Definition:Right Circular Cone(Redirected from Definition:Opening Angle)

## Definition

Let $K$ be a right circular cone.

Let point $A$ be the apex of $K$.

Let $B$ and $C$ be the endpoints of a diameter of the base of $K$.

Then the angle $\angle BAC$ is the **opening angle** of $K$.

In the above diagram, $\phi$ is the **opening angle** of the right circular cone depicted.

## Also known as

The **opening angle** of a right circular cone is also known as its **aperture**.