How to calculate some general area on a sphere for simplicity the unit sphere. Let's say I have a ball and I draw a ring on it. What is its area? I guess I need some initial point (some coordinate). Let's take a spherical coordinates with r=1. Element of area is [itex] \sin(\theta) d \theta d \phi [/itex]. But how to define (describe) a ring? I guess I need some function [itex]\theta(\phi) [/itex] and than integrate over ...what, all or some separate region of [itex]\phi[/itex]? Or what would you suggest? Thank you for your advice and help.