# Definition:Spherical Triangle/Side

## Definition

The sides of a spherical triangle $T$ are the arcs of the $3$ great circles which form the boundaries of $T$ between the points at which they intersect.

In the above diagram, the sides are labelled $a$, $b$ and $c$.

### Length of Side

Let $ABC$ be a spherical triangle on a sphere $S$.

Let $AB$ be a side of $ABC$.

The length of $AB$ is defined as the angle subtended at the center of $S$ by $AB$.