Hello Everybody! Concept of Solid Angle was pretty much straight forward until they were on surface patches were taken into account which were visualized as base of cone. I am having difficult when 3d Objects like Sphere/Cylinder . We can very easily calculate the respective area and plugin the value to find answer but what baffles me is That only a part of the the sphere 'surface area is capture by the cone(say 2pi*(R)^2 instead of 4pi*(R)^2 ) In real life, you can see that: if a ball is at some distance you can only see the part facing you not on the opposite. I google and found one wolfram demonstration which starts with a small patch goes then from there as solid angle covers half of hemisphere,pretty much straightforward And, after that point it starts covering the other half of the sphere , I want to know why we are coniderering a part we are not facing at all (or can't perceive it until we turn our heads around)?