steradian

American  

[stuh-rey-dee-uhn] / stəˈreɪ di ən /

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

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steradian British  

/ stəˈreɪdɪən /

noun

1.  sr.  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

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steradian Scientific  

/ 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/r² 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

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Etymology

Origin of steradian

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