Science Fair Project Encyclopedia
Steradian
The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. The symbol is sr.
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 system in 1995.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details