WHY DO THE SUN AND MOON APPEAR MANY TIMES LARGER AT THE HORIZON?

 
The angular diameter of the sun and moon is about half a degree each. The celestial objects are seen with two eyes. When we observe the horizon, the terrestrial surface with all its objects, such as trees, houses, roads or ground give us a perspective view, i.e., farther the objects smaller they appear, as they subtend smaller and smaller angles at the retina. Through this long distance perspective, which some time extends to several kilometers, our vision is able to realize a long perceptual distance. At the end of this perspective we locate the celestial objects and realize a particular size. On the other hand, when we view these objects in the sky, the most important perspective is absent and consequently the two eyes are left with their own power to discern a distance. This binocular distance limit in the absence of the perspective has been found to be about 500 feet, which vary slightly from person to person. This can be checked by the absence of parallax shifts of objects beyond the distance when we view with alternate eyes. Therefore the sun and moon are located at a distance of about 500 feet must appear much smaller than a similar half degree object at a considerably long perceptual distance realized by the sense of vision with the help of perspective. In order to illustrate this phenomenon, we place a larger ball at a distance from the eye and a much smaller one just covers the angular dimension of the larger ball. Now both the balls subtend the same angle at the eye, but to our binocular vision the larger ball at that distance appears decidedly larger and it is physically larger. Through a telescope or a camera, the sun and moon appear of the same sizes either at the horizon or over the high sky. This view also applies to star constellations at the horizon and at the high sky. Monocular vision by one-eyed people has no illusion of this nature, because they have no perceptual depth.