Originally Posted by P A N

The law of perspective (known to visual artists everywhere) basically states that all visual data will converge on a single point given enough length to do so. The best way I can personally visualize this is to imagine an infinitely long hallway. It's level and square and built perfectly. You can't see the end of the hallway, but the floor, walls and ceiling all have a vanishing point, which is always relative to the observer.

It basically means we can't see infinitely far on an infinite plane, as the ground and sky have to meet in the middle somewhere, and the farther an object (ie the sun) is the smaller it get, eventually disappearing. This can also be observed by watching ships go over the horizon. We think they are going over the curvature of the Earth. But when you pull a telescope out after it has disappeared over the curve, it reappears, top to bottom, because it's being brought back into the range of our site with an aid.