Steradian

steradian.3.jpg

The steradian (sr) is the unit used to express the dimensionless quantity of solid angle.

A sphere subtends a solid angle of 4π≃ 12.57sr for an observer at the centre of the sphere.

This factor appears in the formula for the surface area, SA, of a sphere with radius r:

SA = 4πr2


Study Astronomy Online at Swinburne University
All material is © Swinburne University of Technology except where indicated.