Quote - Something to consider.....If you are on the ground of a hollow world, and you look up, if the atmosphere is the same thickness/depth as that of a normal 'earth' then you would see the opposing side of the hollow planet through two layers of atmosphere..........

Agree, but in my case the shot is parallel to the ground, and I have also the need to show this hollow world on the artwork, without chasing the realism at all costs... :)
It is a book cover... ;) 
Anyway is a not so easy task!