Steradian

Categories: Natural units | SI derived units | Units of measure

The steradian (symbol: sr) is the SI unit of solid angle. The name is partly derived from the Greek stereos for solid.

The steradian is useful to distinguish between quantities of different nature but the same dimension.

In practice, the symbol sr is used where appropriate, but the derived unit "1" is generally omitted in combination with a numerical value. 1 sr = m2·m–2 = 1

The steradian is the 3 dimensional equivalent of the 2 dimensional radian.

As an example, radiant intensity can be measured in watts per steradian (Wsr-1)

The steradian is defined as "the solid angle subtended at the center of a sphere of radius r by a portion of the surface of the sphere having an area r2." Since the surface area of this sphere is 4πr2, then the definition implies that a sphere measures 4π steradians. A steradian can also be called a squared radian.

A steradian is also equal to the spherical area of a polygon having an angle excess of 1 radian, to 1/4π of a complete sphere, or to (180/π)2 or 3282.80635 square degrees .

The steradian was formerly an SI supplementary unit, but this category was abolished from the SI in 1995.

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SI multiples

Multiple Name Symbol Multiple Name Symbol
100 steradian sr      
101 decasteradian dasr 10–1 decisteradian dsr
102 hectosteradian hsr 10–2 centisteradian csr
103 kilosteradian ksr 10–3 millisteradian msr
106 megasteradian Msr 10–6 microsteradian µsr
109 gigasteradian Gsr 10–9 nanosteradian nsr
1012 terasteradian Tsr 10–12 picosteradian psr
1015 petasteradian Psr 10–15 femtosteradian fsr
1018 exasteradian Esr 10–18 attosteradian asr
1021 zettasteradian Zsr 10–21 zeptosteradian zsr
1024 yottasteradian Ysr 10–24 yoctosteradian ysr
da:Steradian

de:Steradiant es:Estereorradián fr:Stéradian it:Steradiante he:סטרדיאן nl:Steradiaal ja:ステラジアン nn:Steradian pl:Steradian pt:Esferorradiano ru:Стерадиан sr:Стерадијан fi:Steradiaani sv:Steradian