Steradian: Difference between revisions
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The '''steradian''', abbreviated '''sr''', is a measure of [[solid angle]], and is the [[SI]] derived unit of solid angle. The unit of solid angle is the solid angle subtended at the centre of a sphere of radius '''r''' by a portion of the surface of the sphere having an area '''r<sup>2</sup>'''. There are 4π steradians on a sphere. | The '''steradian''', abbreviated '''sr''', is a measure of [[solid angle]], and is the [[SI]] derived unit of solid angle. The unit of solid angle is the solid angle subtended at the centre of a sphere of radius '''r''' by a portion of the surface of the sphere having an area '''r<sup>2</sup>'''. There are 4π steradians on a sphere. | ||
A steradian is also equal to the spherical area of a [[polygon]] having an [[angle excess]] of 1 radian, to 1/4[[pi|π]] of a complete [[sphere]], or to (180/π)² or 3282.80635 [[square degree]]s. The central angle of a cone which subtends one steradian is approxiately 1.144 rad or 65.54°. | |||
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Revision as of 10:39, 30 May 2007
The steradian, abbreviated sr, is a measure of solid angle, and is the SI derived unit of solid angle. The unit of solid angle is the solid angle subtended at the centre of a sphere of radius r by a portion of the surface of the sphere having an area r2. There are 4π steradians on a sphere.
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 central angle of a cone which subtends one steradian is approxiately 1.144 rad or 65.54°.