Solid Angles on a Sphere
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A solid angle is related to the surface area of a sphere in the same way an ordinary angle is related to the circumference of a circle. The intersection of the cone with a sphere of radius 1 defines a surface whose area is equal to the solid angle subtended by the cone. The SI unit for solid angles is the steradian. While there are radians in a circle, there are steradians in a sphere.
Contributed by: Bernard Vuilleumier (March 2011)
Open content licensed under CC BY-NC-SA
"Solid Angles on a Sphere"
Wolfram Demonstrations Project
Published: March 7 2011