New designs could help future explorers to answer nature’s call on missions to the Moon. This is because around the time of moonrise the Moon is about 6400 kilometers (about 4000 miles) farther away from an observer's location than when it is high in the sky. In 1813, Schopenhauer wrote about this, that the Moon illusion is "purely intellectual or cerebral and not optical or sensuous. You'll see a giant moon rising in the east. According to the "angle of regard" hypothesis, the Moon illusion is produced by changes in the position of the eyes in the head accompanying changes in the angle of elevation of the Moon. [5] This is because of the eccentricity of the Moon's orbit. The moon often looks huge as it begins to peek up over the horizon, but hours later as you glance up into the night sky you will note that it now appears much smaller.

It's summer. According to this possible explanation for the moon illusion, depth perception plays an important role in how we see the moon at the horizon versus high in the sky. [3] Looking through one's legs at the horizon Moon does reduce the illusion noticeably, but this may be because the image on the retina is inverted. J Exp Psychol Hum Percept Perform. But something's wrong. Ever wonder what your personality type means? It's a real illusion. "[13] The brain is accustomed to seeing terrestrially–sized objects in a horizontal direction and also as they are affected by atmospheric perspective, according to Schopenhauer. Have you ever noticed how the moon looks bigger when it is on the horizon than it does when it is high in the sky?

Extensive experiments in 1962 by Kaufman and Rock showed that a crucial causative factor in the illusion is a change in the pattern of cues to distance, comparable to the Ponzo illusion. When the moon has moved higher into the sky, those depth cues disappear. A similar illusion was discovered in 1913 by Mario Ponzo, who drew two identical bars across a pair of converging lines, like the railroad tracks pictured left. The explanation of this illusion is still debated.[2][3][4]. The 1989 book The Moon Illusion, edited by Hershenson, offers about 24 chapters written by various illusion researchers reaching different conclusions. | Astronomy Essentials | EarthSky

Step outside any evening at sunset and look around.

But since its retinal image is approximately the same size whether it is near the horizon or not, the brain, attempting to compensate for perspective, assume that a low Moon must be physically larger. Foreground objects trick your brain into thinking the moon is bigger than it really is. Immanuel Kant refers to the Moon illusion in his 1781 text Critique of Pure Reason, when he writes that "the astronomer cannot prevent himself from seeing the moon larger at its rising than some time afterwards, although he is not deceived by this illusion". During summer the Sun is high, which means the full Moon must be low. Image Credit: NASA/Aubrey Gemignani. The upper yellow bar looks wider because it spans a greater apparent distance between the rails. This phenomenon is known as the moon illusion. How the Muller-Lyer Illusion Is Used in Psychology, How Psychologists Tested Babies' Depth Perception With the Visual Cliff, The Bottom-Up Processing View of Perception, How Psychology Explains How Expectations Influence Your Perceptions, How Figure-Ground Perception Helps Us Distinguish Scenes, Gestalt Laws of Perceptual Organization and Our Perception of the World, Try the Negative Photo Illusion With This Fun Trick, Effects of the Color Purple on Mood and Behavior, The Uncanny Valley: Why Realistic Robots Are Creepy, Daily Tips for a Healthy Mind to Your Inbox, A simple but powerful theory of the moon illusion, The Natural Moon Illusion: A Multifactor Angular Account.
Most recent research on the Moon illusion has been conducted by psychologists specializing in human perception. It doesn't matter which is correct, though, if all you want to do is see a big beautiful moon. What makes the moon so low? This theory is centered on the idea that when you view the moon at the horizon, you are seeing it in the presence of depth cues such as trees, mountains, and other scenery. Ptolemy attempted to explain the Moon illusion through atmospheric refraction in the Almagest, and later (in the Optics) as an optical illusion due to apparent distance,[7][8] or the difficulty of looking upwards, although interpretations of the account in the Optics are disputed. Moon illusion discussed at Bad Astronomy website, New Thoughts on Understanding the Moon Illusion, Father-Son Scientists Confirm Why Horizon Moon Appears Larger, NASA Astronomy Picture of the Day: Moonrise Over Turkey (16 June 2009),, Articles with unsourced statements from November 2018, Creative Commons Attribution-ShareAlike License, This page was last edited on 9 September 2020, at 01:16. Graphics: This full moon is strangely inflated. This states that the perceived size of an object depends not only on its retinal size, but also on the size of objects in its immediate visual environment. 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. When pictorial cues to an increased distance are added into the vista of the zenith Moon, it appears larger. Cameras don't see it, but our eyes do. This theory is centered on the idea that when you view the moon at the horizon, you are seeing it in the presence of depth cues such as trees, mountains, and other scenery. Most of the rest say it looks larger and about the same distance away as the zenith Moon, with a few people reporting no Moon illusion at all. Why Do People Experience Afterimages as an Optical Illusion? Baird JC, Wagner M, Fuld K. A simple but powerful theory of the moon illusion. Remember, the Sun and the full Moon are on opposite sides of the sky. The moon illusion might be the world's most widely known optical illusion, and it's been pondered for thousands of years. Airline pilots flying at very high altitudes sometimes experience the Moon Illusion without any objects in the foreground. A physicist offers opinions about current theories. For example, 'pinch' the moon between your thumb and forefinger or view it through a cardboard tube, which hides the foreground terrain. Historically, the best-known alternative to the "apparent distance" theory has been a "relative size" theory. Photographs of the Moon at different elevations also show that its size remains the same. However, there are probably complex internal processes behind this relationship. Desaguliers (1736), W. Porterfield (1737), R. Smith (1738), C.N. ", On the Fourfold Root of the Principle of Sufficient Reason, "Moon Illusion Explained on the Basis of Relative Size". At its zenith, the moon appears much smaller because it is surrounded by the large expanse of the sky. [1][2] Between different full moons, the Moon's angular diameter can vary from 29.43 arcminutes at apogee to 33.5 arcminutes at perigee—an increase of around 14% in apparent diameter or 30% in apparent area. Block, MD, Luca Libralato Photography / Getty Images, 10 Cool Optical Illusions and How Each of Them Work. A fun activity: Look at the moon directly and then through a narrow opening of some kind. Remember, the Sun and the full Moon are on opposite sides of the sky. The moon is seen as it rises over the Capitol, Sunday, Nov. 13, 2016 in Washington, D.C.

Experiments by many other researchers have found the same result; namely, when pictorial cues to a great distance are subtracted from the vista of the large-looking horizon Moon it looks smaller. An apparent distance theory evidently was first clearly described by Cleomedes around 200 A.D. It looks like Earth's moon, round and cratered; the Man in the Moon is in his usual place. [9] Similarly Cleomedes (about 200 A.D.), in his book on astronomy, ascribed the illusion both to refraction and to changes in apparent distance.

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