The contact angle between a sphere and a tangent plane is the angle α between the normal to the sphere at the point of tangency and the basal plane with respect to which sphere cross sections are measured (i.e., a plane perpendicular to the chosen z-axis). In the above figure, α | = | cos^(-1)(a/R) | = | sin^(-1)((R - h)/R).

dihedral angle | normal vector | sphere | spherical cap | tangent plane