Moon illusion
The Moon illusion is an optical illusion, appearing by the moon and the sun near the horizon is greater than at higher altitude in the sky, although there is no physical or astronomical cause. The cause of this psychological perception phenomenon is not finally resolved.
In relation to the visual angle of the thumb an outstretched hand of the visual angle of the moon corresponds regardless of the stage of actually depicted on the adjacent picture right smallest moon disc, even if most people would tap from memory rather on the size of the Moon is shown on the left. The apparent diameter of the moon is 31 arcminutes, or about 0.5 degrees. Three to four slices moon to appear side by side at the same angle of view as the width of the extended thumb, the thumb, depending on the width or length of the arm is between about 1.5 and 2 degrees.
- 3.1 Notes and references
- 3.2 Literature
- 3.3 External links
History
The first indications of the phenomenon of the moon illusion can be found on clay tablets from the royal libraries of Nineveh and Babylon ( 6th century BC). Ptolemy (c. 150 AD) falsely suspected magnifying properties of the atmosphere, Alhazen (Abu Ali Al -Hasan Ibn Al- Haitham, 965 to about 1040 ) already wrote of flattened firmament, Leonardo da Vinci, Johannes Kepler and René Descartes dealt with the moon illusion, for over 100 years, this optical illusion is being investigated by the scientific psychology of perception, yet the phenomenon of the moon illusion is still not clearly understood. There remain inconsistencies in the different explanatory approaches. The currently most recognized and substantiated by many experiments, observations are the wrong -assessed the distance with the flattened firmament and the principle of comparison objects.
Explanations
It is often mistakenly believed that the deception a consequence of " redness " is - by the Rayleigh scattering is much more blue than red light scattered out on the atoms and molecules of Earth's atmosphere from the observer directed beam of rays of the sun and moon near the horizon, so that a larger proportion of red light passes to the eye of the observer. Also it is not a consequence of the refraction ( that is, the refraction of light rays at the interface of two media). However, a refraction was carried out by resizing or redness should also be seen on a photograph, but this is not the case.
The flattened firmament
Visual angle and size perception
Essential for the correct size perception of an object is the equally correct information on its actual distance to the observer. From the size of the image ( the visual angle ) of an object on the retina and the co-existing knowledge of its distance " calculated " the human brain subconsciously the actual size of the object ( Emmer Tsches Act ) by drawing on the experience that a close object a larger image onto the retina causes the same as, more distant object. Since the distance of the moon to the earth during the movement on its elliptical orbit changes only by about 10 % and thus remains within one night under one percent, it shall register with the alleged substantial increase in the size of the moon to the establishment and demise be a deception.
Perceptual illusions as to the size generally occurs when an unconscious false estimate of the distance is present: an object (D) in a fixed distance ( f ) generating an image in size (A) on the retina, and its removal mistakenly underestimated ( e ), it is perceived as less than or just as large (C), as it would be in order in this underestimated shorter distance the size ( A) to be formed on the retina ( see the diagram above). An example of this is the high- Moon or even the so-called " toy car " effect: If you look down from a high tower, is lack of experience underestimated the distance and the cars are down less, such as toy cars, perceived.
Conversely: an object (C) in fixed distance (e ) generating an image of the size (B) on the retina, and the distance mistakenly overestimate (f), will be perceived as more or as just large (D) as he would have to be to produce in this overrated greater distance the size ( B) on the retina ( see sketch). An example of the moon near the horizon, the " Moon illusion " is Da between the moon on the horizon and the viewer much more objects (trees, houses, hills, etc. - more " low information " ) than between the moon up in the sky and the viewer, the Distance mistakenly considered greater, with larger distance and same size image on the retina of the subject but would be greater, and thus the moon or the sun is perceived even larger on the horizon.
Depth information
Through the depth information ( trees, houses, etc.) in a horizontal way of looking at the horizon and the lack of depth information on looking up receives the firmament, are apparently on the moon, the sun and the stars, a flattened shape. In real equal-sized image on the retina of the eye of the seemingly more distant moon on the horizon of seemingly less distant moon at a higher level is perceived larger and smaller.
Because of the flattened shape of the firmament and the individual stars of a constellation (for example, the constellation Swan) perceived as further apart, the whole constellation appears therefore larger when it is near the horizon than when it is at its zenith: And it is continuously smaller when it is coming closer to the zenith, for example during a night of Eastern horizon ago. There is this continuous and linear dimensional change as a function of position in the sky while at the constellations, but not so clearly in the moon or the sun. The apparent change in size of the Sun and Moon falls - in contrast to the perception of size in the constellations - only near the horizon on.
For the explanatory principle of the flattened firmament speaks that only thus the apparent continuous change in size of the constellations can be explained, while the principle of comparison objects (see below) can better explain why a change in size of the sun and moon will only be perceived near the horizon.
Comparison objects
For the apparent size change also the principle of comparison objects adds: Because the moon on the horizon in comparison with smaller objects, such as trees or houses is seen, it affects greater there than if he is seen standing tall in comparison with the great firmament. Addition, there is a paradox: the greater distance because of the seemingly " on the horizon " greater perceived moon appears to be closer back then because of its unusual size. This paradox could be resolved as follows: There is a mix here deceptions by two principles of distance perception:
- More things ( depth information and perspective ) between mean a greater distance,
- A larger object is closer.
It should be noted here that the moon is also perceived very large on the horizon, if there is no comparison smaller objects, such as in the desert or on the sea. The horizon is appreciated very far from there because of the unobstructed viewing and there is much perspective depth information. This contradicts the exclusive explanation of the phenomenon by smaller objects of comparison and is therefore more likely to be regarded as evidence for the principle of the overestimate of distance.
Variable range of perception
In this hypothesis, the visual system is equivalent to a data channel. While the image on the retina may contain a lot of information, provides the further neural processing of the image to perform a bottleneck: per second can be transmitted and processed only a certain amount of information, so only a limited number of picture elements are identified. With these you can indeed either show a larger or smaller image detail or perceive, but a smaller section shows more detailed information, since the pixels are then packed more densely. A larger cut again has the advantage of the survey. If one adds to that of each selected area - large or small ( on the left) - is projected on a monitor or a kind of inner memory of constant size in the visual system (right), then there is the Moon illusion this way:
Due to the limited channel capacity, only a section of the retinal image is processed for perception. If the detected area is small, then convey the identified image elements a high detail resolution. A single item will make a great contribution to this area and therefore appear great, even the moon. In a large perception angle the resolution is correspondingly lower, also affects everything - as projected on the same area - correspondingly smaller. The constant size "internal monitor " stands pictorially for the notion that the visual system in the consideration of a large as well as a small area always uses his full data capacity to capture a comparable number of characteristic details in both cases.
That the perception of size having the resolution of details was related guessed already Goüye (1700). He compares the moon behind trees and branches with a column which appears thicker when it had grooves. Lühr (1898 ) and Cornish (1937 ) expressed the idea that the visual perception concentrate on a limited but variable in its size range. While Lühr discussed deep or high in the sky standing constellations, Cornish justify any difference in size perception of the sun on the horizon with its shape ( flat or high).
Experiments to measure the perceived size of a bright circular disc was performed by Erna Schur or by Lloyd Kaufman and Irvin skirt. While Schur found a large increase in the perception in the horizontal viewing direction relative to the vertical even at near- terrestrial stimuli, report Kaufmann and rock that a virtual disc appeared in the vertical direction of view greater when the natural horizon was displayed via a mirror in the line of sight.
In evolutionary periods, the brain has learned automatically a smaller area to take on the horizon in the eye, to as early as possible to identify structures that promised food or shelter or even competitors and predators betrayed. A scenic capture - waiving high resolution - was chosen when it eg went somewhere in the wide sky to assess the weather or finding a flock of birds.
An unusually large celestial bodies observed on the horizon when this highlights as the dominant light source, the details sharp and contrasty in his area. The endeavor of the visual system, because of the prevailing conditions of good visibility also particularly good resolve small objects, setting a correspondingly small perception angle, which then also the moon ( or the sun ) causes automatically enlarged. In the earthly objects of the magnification effect is not noticeable so because you constantly see them from different distances and thus also vary in size, while stands for celestial bodies with their always the same extent an apparent size change more striking.