The position of a point $P$ can be specified using Cartesian coordinates $(x,y,z)$ or spherical

coordinates $(r,,),$ where $r$ is the radial distance of $P$ from origin of the $\{hat(x),$hat$(y),$hat$(z)\}$

coordinate system. Angles $$ and $$ denote azimuth and elevation angles respectively

as shown in the below figure. The unit vectors $\{hat(i),$hat$(j),$hat$(k)\}$ form the spherical coordinate

system to represent any arbitrary point $P$ on the sphere.