steradian

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ste·ra·di·an (sr),

(stĕ-rā'dē-ăn),
The unit of solid angle; the solid angle that encloses an area on the surface of a sphere equivalent to the square of the radius of the sphere.
[G. stereos, solid, + radion, radius]

steradian

(stē-rā′dē-ăn)
The unit of measurement of solid angles. It encloses an area on the surface of a sphere equal to the square of the radius of the sphere.
References in periodicals archive ?
Provided that the surface of the flat sensor is held perpendicular to a line from the source to the sensor, measurements with a flat sensor can also be used to estimate fluence rate provided three conditions are met: (1) there is a single UV source; (2) reflections from room surfaces, particularly those that are not within the 2[pi] steradian viewing angle of the flat sensor, are not significant; and (3) the sensor is not too close to the source.
For a cylindrical sensor, however, the conditions that need to be met will be less stringent than for a flat sensor: (1) measurement of fluence rate for multiple sources may be feasible; (2) reflections from room surfaces will be received over a 4[pi] steradian viewing angle; and (3) when the UV source is a linear lamp, a cylindrical sensor allows measurements to be made significantly closer to the source than a flat sensor provided the sensor is properly oriented.
By noting that the effective area of an antenna is equal to G[lambda.sup.2]/4[pi] (where G is the gain) and integrating over all 4[pi] steradians of space, the total power delivered to the load can be calculated.
By combining equations and noting that a 0.5 [Degrees] cone angle is equivalent to 6 x [10.sup.-5] steradians, an expression can be obtained for the noise flux density of the sun (in W/[m.sup.2]-Hz):