Solid Angle Subtended by a Circular Aperture

Abstract

Methods for calculating the solid angle subtended by a circle at an off‐axis point are correlated and the rates of convergence of available series are compared. Averages over a plane surface or a cylindrical volume are derived from an analogy that permits the use of existing tables of mutual inductances. Rates of variation, for displacement or rotation of the source, and the technique of computing from the zonal harmonic series are briefly discussed.