Square degree

A square degree (deg2) is a non-SI unit measure of solid angle. Other denotations include "sq. deg." and (°)2. Just as degrees are used to measure parts of a circle, square degrees are used to measure parts of a sphere. Analogous to one degree being equal to  radians, a square degree is equal to ()2 steradians (sr), or about  sr or .
The whole sphere has a solid angle of which is approximately :