an SI unit of solid angle; the angle that, having its vertex in the centre of a sphere, cuts off an area of the surface of the sphere equal to the square of the length of the radius
Symbol: sr
Word origin
C19: from stereo- + radian
steradian in American English
(stəˈreɪdiən)
noun
the basic unit of solid angular measure in the SI system, equal to the solid angle subtended at the center of a sphere by an area, on its surface, that is equal to the square of its radius:one sphere equals 4π steradians