steradian

[ stuh-rey-dee-uhn ]

noun

, Geometry.

1. a solid angle at the center of a sphere subtending a section on the surface equal in area to the square of the radius of the sphere. : sr

steradian

/ stəˈreɪdɪən /

noun

1. 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 sr

steradian

/ stĭ-rā′dē-ən /

1. A unitless measure of solid angles. A solid angle projecting from the center of a sphere and cutting its surface has a measure of s r ² steradians, where s is the surface area of the sphere cut out by the solid angle, and r is the radius of the sphere.
2. See also radian

Word History and Origins

Origin of steradian¹

First recorded in 1880–85; ste(reo)- + radian

Word History and Origins

Origin of steradian¹

C19: from stereo- + radian

Example Sentences

For the record, the amount of extra light they found bouncing around the universe is about 10 nanowatts per square meter per steradian, a measure of solid angle on the sky.

From New York Times