Steradian, unit of solid-angle measure in the International System of Units (SI), defined as the solid angle of a sphere subtended by a portion of the surface whose area is equal to the square of the sphere’s radius.

TheSIunitofsolid angleisthesteradian (sr).The solid angleof a complete sphere is 4π sr.The solid anglecorresponding totheface of a cube measured atthecentre is 2π/3 sr. One steradian is equal to (180/π)2square degrees.

Steradian,unitofsolid-anglemeasure in the International System ofUnits(SI),definedas thesolid angleof a sphere subtended by a portion of the surface whose area is equal to the square of the sphere's radius.

Steradian,unitofsolid-anglemeasure in the International System ofUnits(SI),definedas thesolid angleof a sphere subtended by a portion of the surface whose area is equal to the square of the sphere's radius.

The solid angle is the angle created in three-dimensional space that an object subtends at a point. Solid angle is a measure of how big an object appears to an observer when looking from that point. The symbol for solid angle is Ω (Greek letter omega).

A solid angle can be defined in terms of an area on the surface of a sphere which is centred at the vertex of the angle. This is the equivalent of defining a planar angle in terms of the length of arc on a circle subtended to the centre. Solid angle can also be defined as an angle formed by three or more planes intersecting at a common point (the vertex). The SI unit of solid angle is the steradian (sr). The solid angle of a complete sphere is 4π sr. The solid angle corresponding to the face of a cube measured at the centre is 2π/3 sr. One steradian is equal to (180/π)2square degrees.

three-dimensional analogue of an angle, such as that subtended by a cone or formed by planes meeting at a point. It is measured in steradians