A New Explanation for the Moon Illusion

The mystery of the Moon illusion is still unsolved, even though various explanations have been offered over thousands of years. Here it is proposed that the illusion may be ascribed to an unusual optical atmospheric effect. The considerably thick spherical atmosphere may form a natural convex lens to converge light rays, which leads to the situation that the light rays from the Moon are greatly compressed inward before they reach an Earthly observer, and thereby the size of the retinal (camera) image of the Moon is diminished. The difference of the optical path in the atmosphere results in the effect that the image size of the horizontal Moon is diminished much more than that of the zenithal Moon, but inversely, the geometry of optics yields a larger enlargement for the horizontal Moon than for the zenithal Moon when they are observed back into the sky. Background A pre-scientific age Chinese reference described that Confucius in his travels found two boys arguing about the distance to the Sun. One said that the Sun was much larger at sunrise than at noon and must therefore be closer to us in the morning, while the other argued that the Sun is much hotter at noon and must therefore be closer to us in the middle of the day. Confucius was unable to resolve the dilemma. Over thousands of years many people were commonly perplexed by a similar phenomenon that the Moon appears larger at the horizon than in the zenith. The same phenomenon also occurs for constellations. As this phenomenon cannot find proof in measurement, this leads to it to be called (first in 1925) the celestial illusion. For an Earthly observer to experience the Moon illusion, he undergoes such a process as follows: a) a ray of light is first reflected (emitted) from the Moon to reach the apex of the Earth’s atmosphere; b) it then passes through the atmosphere to enter his eyes; c) excitation of his psychological system gives birth to a comparison of perceptual image and retinal image. This process involves several disciplines such as physics (optics), meteorology, astronomy, psychology, and physiology. A physical explanation was first considered by early authors like Aristotle, Posidonius, and Ptolemy, who thought that some atmospheric (refraction) process intervenes to produce magnification for the horizontal Moon. The atmospheric refraction implies that the horizontal enlargement is measurable, however, no such enlargement has been found by any astronomical