Appearances vs. Facts
The phenomenon of the disappearance of a ship, hull first, as it recedes from view, is caused by the same law of foreshortening as that which governs the disappearance of the rail, or causes the two rails to appear to approach each other. If we should make calculations on the basis of the appearance instead of on the basis of the fact that the rails do not approach, but only seem to, we necessarily draw false conclusions. This is precisely what the astronomers do. They conclude from appearances rather than from facts.
(Red colorization mine.)
As one focuses further out, one focuses on more light; hence, more objects occupy its field of vision and, therefor, increase the object-density thereof. However, the disappearance of (notbatman) occurs when light from a body that was, previously, in view reaches neither the cones nor the rods of the retina (e.g., for the obstruction thereof).