Consider S be the area of surface subtended by the intersection of the sphere and the cone. The solid angle is defined Ω = (S/r²). This defines the solid angle in steradians. If the surface covers the entire sphere then the number of steradians is 4π.

What is the solid angle subtended?

A steradian is the solid angle subtended at the center of a sphere of radius r by a section of its surface area of magnitude equal to r2. Since the surface area is 4πr2, there are 4π steradians surrounding a point in space.

What is the formula for calculating solid angle?

The formula of the solid angle(Ω) is, Ω=Area of part of the spherical surface subtended divided by the radius of the area of the part of the spherical surface subtended. That is, Ω=Ar2.