I was wondering if anyone would make that point, glad to see you did! Personally, I'm undecided on the flat-earth matter (I consider it up for real debate, and do what I can to weed out fallacies on both sides). Anyways, you are exactly right: air can often be thought of as a very thin fog. Over a great distance, there are just too many particles to see through. Not to mention that the amount of magnification necessary to see from America to Mt.Everest would be extreme (assuming that one could get a clear sight-line, that is)