Steradian | SystemeInternationalUnit | SI SolidAngleMeasure. Symbol: sr. It is 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. Another definition is: the solid angle which, having its vertex in the center of the sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere. Steradian = m^2/m^2 = 1 | Physical | MeasureFn | MagnitudeFn | ConstantQuantity, FunctionQuantity | (=> (and (instance ?REL RelationExtendedToQuantities) (instance ?REL BinaryRelation) (instance ?NUMBER1 RealNumber) (instance ?NUMBER2 RealNumber) (holds ?REL ?NUMBER1 ?NUMBER2)) (forall (?UNIT) (=> (instance ?UNIT UnitOfMeasure) (holds ?REL (MeasureFn ?NUMBER1 ?UNIT) (MeasureFn ?NUMBER2 ?UNIT)))))
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