# solid angle

A solid angle is a three-dimensional angle formed by a conical surface (see cone).
Considering its vertex to lie at the center
of a sphere, then a measure of its magnitude
may be obtained from the ratio between the area (*L*^{2})
of the surface of the sphere cut off by the angle, and the square (*R*^{ 2})
of the sphere's radius. Solid angles are measured in steradians (sr), an angle of one steradian subtending an angle of area *R*^{ 2} at a distance *R*.

See also angle.