==accessibility== 
 Like a lot of WP articles on science, this one IMO lacks accessibility. It starts out with a definition in terms of the vector cross product. Oops, sorry, 99% of WP readers aren't conversant with the vector cross product. We need some basic, simple examples without math. WP articles are supposed to be intelligible to the general reader; sections in this article such as Relation to spherical harmonics are not accessible to anyone without at least an undergraduate degree in physics.