Is there a general formula to use to determine the amount that a distant object is obscured by the horizon?
Here are a couple of examples:
I can view the mountains that are 70 km away. I am at or very near to the ground. If we assume that the intervening terrain is negligible, how much of the mountains are obscured below the horizon?
A ship that stands 30m to the tip of the mast sails out onto the sea. At what distance does its mast finally vanish completely out of sight?
Of course, we need to assume a spherical Earth with a radius of 6371km.