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The Moon illusion is an optical illusion which causes the Moon to appear larger near the horizon than it does higher up in the sky. It has been known since ancient times and recorded by various cultures.〔Wade, Nicholas J (1998). A natural history of vision. A Bradford Book. p. 377 ff.〕 The explanation of this illusion is still debated. 〔McCready, Don, Professor Emeritus, ("Finally! Why the Moon Looks Big at the Horizon and Smaller When Higher Up" ), Psychology Department, University of Wisconsin-Whitewater, Revised November 10, 2004, retrieved October 31, 2015〕 ==Proof of illusion== A popular belief, stretching back at least to Aristotle in the 4th century B.C., holds that the Moon appears larger near the horizon due to a real magnification effect caused by the Earth's atmosphere. This is not true: although the atmosphere does change the perceived color of the Moon, it does not magnify or enlarge it. In fact, the visual image of the moon is about 1.5% smaller when it is near the horizon than when it is high in the sky, because it is farther away by nearly one Earth radius. Atmospheric refraction also makes the image of the Moon slightly smaller in the vertical direction. The angle that the full Moon subtends at an observer's eye can be measured directly with a theodolite to show that it remains constant as the Moon rises or sinks in the sky (discounting the very small variations due to the physical effects mentioned). Photographs of the Moon at different elevations also show that its size remains the same.〔Lynch, D and Livingstone, W (2001). Color and Light in Nature. Cambridge University Press. par. 7.10〕 A simple way of demonstrating that the effect is an illusion is to hold a small object (say, wide) at arm's length () with one eye closed, positioning it next to the seemingly large Moon. When the Moon is higher in the sky, positioning the same object near the Moon reveals that there is no change in size. Note that between ''different'' full moons, the Moon's angular diameter can vary from 29.43 arc minutes at apogee to 33.5 arc minutes at perigee—an increase of around 14% in apparent diameter or 30% in apparent area.〔(Astronomy Picture of the Day — large and small full moons ), NASA〕 This is because of the ellipticity of the Moon's orbit. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Moon illusion」の詳細全文を読む スポンサード リンク
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