Symbol sr. The supplementary SI unit of solid angle equal to the solid angle that encloses a surface on a sphere equal to the square of the radius of the sphere.
Mathematics
Seesolid angle.
Astronomy
The unit of solid angle: an angle in three dimensions, as for example subtended by the base of a cone. One steradian encloses an area on the surface of a sphere that is equal to the square of the sphere’s radius. The solid angle subtended at the centre of a sphere by its entire surface is 4π steradians.
Chemistry
The dimensionless (supplementary) SI unit of solid angle equal to the solid angle that encloses a surface on a sphere equal to the square of the radius of the sphere.
Chemical Engineering
A supplementary SI unit defined as the solid angle which, having its vertex in the centre of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere.