Steradian

**Semantic type:** Quantitative Concept

**Definition:** A SI derived unit of solid angle measurement. One steradian is the solid angle that, having its vertex in the center of a sphere, cuts off an area on the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere. It is equal to 0.25 of the solid angle around a point, 0.07958 sphere, 0.15916 hemisphere, 0.6366 spherical right angle, 3,282.8 square degrees. The solid angle corresponding to all of space being subtended is 4pi steradians.

**Synonyms:** - sr - sr - sr - steradian - steradian - str