I have always wonder if the apparent or visible junction of the Earth and sky is a little elusive, at least.  Maybe a metaphor. Or maybe it is all about the perspective.

 

Imagine you are on a spaceship looking down on Earth. Now imagine a person standing at one point on the surface of the Earth.  The horizon seen from that person in space will be a circle of so many miles in diameter and if the ship moves the circle that circumscribes the horizon changes as well. Hence new things come into the horizon and other things fall out of it.