The Moon Illusion Issues - Essay Example

Introduction This writing reviews explanations and supporting theories about "The Moon Illusion," the phenomenon experienced by most people watching the moon rise above the horizon. The moon appears to be perceptibly bigger than it looks hours later that same night when it is much higher in the sky. Does it really look bigger Is it an optical illusion Is it always the same size and, thus, a person's eyes play tricks What do the explanations say Background Studying the collective body of works about "The Moon Illusion" that experts have produced throughout the ages, one conclusion seems certain: They've agreed to disagree! However, some experts note the same illusory phenomenon happens to the sun as well as constellations. (Plait, 2008) (Simanek, 2002) The "experts" hail from astronomy and astrophysics, geometry and mathematics, philosophy and psychology, physics and light-wave science (as in electromagnetic spectrum visible light), and, of course, NASA (the National Aeronautic Space Administration). Some who try to explain the Illusion say and have said they're not experts as much as they are admirers of moonrises and moonlit nights. They noticed the Illusion phenomenon and thoughtfully pondered it. They've invested time and energy toward solving the mystery. So, in some explanations trying to account for the Moon Illusion, besides intellectual calculations, often there are emotional components, akin to "Beauty is in the eyes of the beholder." Explanations are centuries old as well as comparatively new. They run the gamut in-between. Champions of various ideas don't usually have adversarial confrontations. Rather, ongoing dialogs center around this theory compared to that theory. Some theories proffer physical rationale and/or geometry. Others theories propose, "It's all in your head!" The old saying goes, "The truth probably lies somewhere in between." A combination of scientific physical factors and psychological emotional factors is definitely within the realm of possibility. See for Yourself The website named "Sandlot Science" asserts that about 85% of people are able to see the Illusion. The interesting questions are, "What about the other 15% Why don't they see it" Some mathematics-based explanations purport that the moon is always the same size. Thus, the 15% merely see reality. The other 85% are playing tricks on themselves. Nonetheless, for anyone in the 15% who has not seen the Illusion and is curious to see what 85% of their fellow Earthlings see, this link to SandlotScience.com has an interactive graphic display showing the Illusion phenomenon. http://www.sandlotscience.com/Moonillusion/Moon_Illusion_Demo.htm The moon's size may be exaggerated somewhat in Sandlot's simulation. Near the horizon it is 150% of the size that it is high in the sky (the top right corner of the simulation). Then again, maybe 150% is not stretched quite as much as a fish story about the size of one that got away. During some nights, people report seeing the moon bigger on the horizon than on other nights. Why is that Science-minded people notice that this is often true about summer nights. Here is one physical theory. Air is hotter in summer. Heat radiates from Earth's surface after sunset. It permeates upward. In the summer this happens on roads, in deserts and elsewhere depending on how cooked a surface gets from the sun beating down on it. To the human eye it looks like shimmering heat waves rippling upward from the baked surface. The shimmer and ripple effect is distortion caused by heat. Heat wave distortion rippling around the image of hot objects makes them look larger than on normal days when heat waves aren't visible. Air is a fluid. Light refracts in fluid. Heat coursing in a fluid can distort appearances of objects seen through the fluid. Because of the rippling nature of the heat waves, an object's appearance ripples a little bit to the left, a little bit to the right, a little bit up, and a bit downward. Ergo, visibly the object's image enlarges perceptibly in all directions. The image shimmers outward from its center. People reckoning such visual size discrepancies of the moon say it looks 10% to almost 50% bigger than its normal size in the middle of its arc across the night sky. Near the horizon as seen through the radiantly-heated lens of a fluid-atmosphere, the moon appears to be 110% to 150% of its normal mid-sky size. See this in the SandlotScience.com simulation. Geometry-based Explanations The moon orbits in almost a perfect circle around Earth. However, it's not perfect. Distance varies from 222,750 to 254,187 miles (356,400 - 406,700 km). (Hawley and Smith, date unknown) That's approximately 31,500 miles of variance or one-eighth (13%) of an orbit that averages 238,500 miles. This augments the "larger-closer" argument. The human eye sees the moon orbit as near to and as far away from the Earth as it gets. The eye sees the moon at two distances and one distance is 13% physically nearer. Visual memory is able to perceive a 13% change in size. A human vision/sight system discerns that at its closest point of approach to the Earth the moon's image looks bigger low on the horizon through a radiantly-heated atmosphere when it is seen in evening and nighttime darkness. "Moon-pie face" is a not-so-flattering descriptor of a person's physical appearance. The human eye works with memory. This vision/sight system is discriminating. It sees when something is normal sized, or if it's bigger or smaller than the image the human mind holds as normal. Hold a tin pie plate facing you at arm's length. It looks big enough; head sized or more. Bend your elbow. Bring the pie plate 13% closer. Suddenly, it's a moon-pie. It looks abnormally big, slightly larger-than-life compared to visual memory. Some people's faces appear to be on that slightly-larger-than-life scale. They've been described as having moon-pie faces because the human memory relates it to the sight of a big moon. Geometry proponents discuss the Moon Illusion by citing the provable fact that the moon is only 0.5 degree big in the sky as measured by instruments (Simanek, 2002). They say the moon's 0.5 size remains rather constant despite human perception. Time-lapse photography supports this assertion. The moon usually measures exactly the same on each frame of photographic film. Slight, almost imperceptible anomalies are possible. But, film is an objective medium unable to fall victim to the subjectivity in the human mind. Film doesn't see things that aren't there. The human mind does. So, the 0.5 argument seems logical because it's provable. Physics professor Donald Simanek's "opinion paper" draws ideas from several references, and credits 20 authors of 26 hardcopy works about the Moon Illusion, plus six websites. His opinion paper asserts the Illusion is not an atmospheric aberration. In fact, he writes that the image of the moon on the horizon diminishes 1.7 - 2% on the retina because visible light of the moon's image must travel through one radius of atmosphere. One radius is the distance from where the observer stands to the end of the atmosphere as it exists between the naked eye and the moon. Along all 360 that the moon gazer can look to the horizon, the atmosphere is very much the same thickness. However, one radius of atmosphere diminishes in thickness when the moon gazer looks higher in the sky; even to the zenith of the sky (directly overhead) or the zenith of the moon's arc at points that are lower than directly overhead. To understand better that eyes look through more atmosphere to see to the horizon, study a visual depiction at http://www.lhup.edu/dsimanek/3d/moonillu.htm below the subheading, "What it's not." How can the atmosphere's radius diminish in thickness It's like this. When looking at the zenith, the eye looks through the shortest distance between two points; the point where the observer stands and the point of the outermost edge of the atmosphere. Looking to the horizon is the longest distance to the atmosphere's outer edge. It necessitates seeing through the entire arc or crown of the atmosphere as it sits upon the earth. This causes refraction of light waves. Opposite of the radiantly-heated fluid atmosphere idea that reckons scattered light causes refraction to swell the moon's image, Simanek presents the idea that more atmosphere reduces the amount of light. Diffusion and refraction shrinks the moon 1.7 - 2%. Simanek also says that due to the eye's interaction with brain psychology, an eye doesn't discern 1.7 - 2% variance, although it sees it, as much more than a "flattening out" of the bottom of the moon as it sits near the horizon. This steers discussion of the Moon Illusion toward theories of human perception and away from unerring geometry. The Eye of the Beholder While Simanek examines several Moon Illusion explanations and presents deeper analyses, at one early point he writes that the 2% size decrease opposes the popular perception. Shrinking 2% is not the typical Moon Illusion swelling. With this he seems to drop the 'It looks bigger!' phenomenon on the doorstep of psychological perception which leads to "brain processing" as it "synthesizes multiple cues" (Simanek - see two paragraphs above "A Ponzo Illusion"). This psychological effect opens a path to explanations about visual perception by, for example, philosophers. One is the famous Irish philosopher, George Berkeley, Bishop of Cloyne (1685-1753). His view, stated here in a paraphrased way for simplicity sake, was akin to "I think. Therefore, I am." Actually Bishop Berkeley propounded a philosophy that "the existence of Matter or corporeal substance" won't "exist whilst they are not perceived." (Berkeley, circa 1710-1743) It seems to be a variation of the conundrum, "If a tree falls in forest and nobody was there to hear it, did it make a sound" From there, Berkeley goes on to postulate that, "it must be remarked that the infinite divisibility of Matter is now universally allowed" and, "Hence, it follows there is an infinite number of parts in each particle of Matter which are not perceived by sense." (Berkeley, "A Treatise Concerning the Principles of Human Knowledge", page 26, Section 47.) Berkeley's premise seems based on two points. First, humankind has limited abilities of perception. Second, corporeal matter is comprised of infinite parts. He used those points to say that when a person's senses become acutely attuned, that person can finally perceive more of the infinite parts in the whole. Illustratively, a modern analogy today is when a radio fails to receive 100% of a radio station's broadcast until the radio's dial is tuned-in 100%. Mistuned a little to the left or right, the radio emits static. If it's completely mistuned, the radio won't get the broadcast at all. To carry the acutely-tuned radio analogy to Berkeley's next and key precept regarding the Moon Illusion, it's best to return to the Bishop's own words. In proportion therefore as the sense is rendered more acute, it perceives a greater number of parts in the object, that is, the object appears greater, and its figure varies, those parts in its extremities which were before unperceivable appearing now to bound it in very different lines and angles from those perceived by an obtuser sense. And at length, after various changes of size and shape, when the sense becomes infinitely acute the body shall seem infinite. During all which there is no alteration in the body, but only in the sense. So, a moon gazer who is very acutely focused sees the moon with keenly perceptive eyeballs that see all. Thus, perception is greater and the moon looks bigger. Returning to the 15% -vs- 85% ratio of people who don't see the Illusion compared to those who do, Berkeley's premise infers that the 15% simply don't attune their visual acuity for keen sightedness. The other 85% can be 'hawk-eyes' when they concentrate intently. Other philosophers and philosophies through the ages have propounded visualization. Psychology calls it "guided" as in guided dreams or fantasies, for example. It's not so much that Berkeley took that tack. Instead, he preached people see things as they perceive them. That rationale has been labeled "subjective idealism." Berkeley alludes to perception becoming reality when a person's mind focuses intently and specifically on an object, a situation, motion or image, etc. It's as intense, for example, as the perception of time during an accident. Living through an accident as it unfolds, a person often sees it in slow motion. Time expanded for the spectator to see every detail. Simultaneously, memories flew by, events in that person's life compressed so s/he later says, "My life flashed before my eyes." That is intent focus and concentration, even if only for a split second. That person perceives things with acute senses as Berkeley wrote. This principle of opening the mind and intently focusing it concurrently on the object-of-the-moment is a recurring theme throughout many of the 125+ sections of the compilation of George Berkeley's writings/essays (called "sections") in "A Treatise Concerning the Principles of Human Knowledge". Berkeley drew counterpoints. Detractors asked, "If people control their own perceptions by focusing intently on what they sense [or 'see' in the case of the Moon Illusion], then why do people perceive the same reality Shouldn't perceptions differ from person to person" Instead, people seem to perceive and see things the same; almost exactly if not entirely exactly the same way. Berkeley deferred to God as the Source of why and how people have the same perceptions. This returns to emotionality regarding how the Moon Illusion is perceived. Brain Reconciles What the Eye Sees How the mind works is a gateway to several other explanations for the Moon Illusion. There are two words that capture (as much as 'capture' is possible) the essence of these concepts. "Anisotropic" is a word that means 'the exhibition of different values when measured in different directions'. "Veridical" is a word for 'truthful, not illusory'. Both concepts are somewhat abstract, but they are cogently married in explanations that try to explain the Moon Illusion. 'Veridical' when applied to something means that experience is factored into the big picture. The brain takes the two-dimensional (or mostly looking two-dimensional) thing the eye sees and processes the retinal image. Processing adds or "factors in" information known from experience. So, a ball is known to have depth and be semispherical on the backside where the eye can't yet see. Nonetheless, its depth is perceived. The mind fills in details about the top of an airplane when the earthbound eye sees only the underside of an airborne plane. Veridical is the automatic completing of the image in the mind's eye, based on the experience of the mind. 'Anisotropic' is similar but the mind has less known data with which to work, so it tends to truncate questionable images. Visual input is incomplete and beyond the mind's experience. So, when the mind lacks experiential references, it can't do veridical magic to complete the image on the retina. The image is perceived in the mind as a cognitive anomaly. To completely process what the eye sees, because the mind can't do a veridical painting of the picture, it conveniently reconciles the image. It merges known visual cues and their real-life reference points with the image's not fully explainable visual cues. In plainer English, the brain wants a tidy package - no incongruent loose ends. It wants cognizance and harmony. So, it reconciles visual input of open-ended images that are beyond full understanding. It resolves an anisotropic image into something with which the mind can live. For example, the sky is too big. It's beyond most minds' capability to process spatial relations. So, at night, the typical mind adds a black screen or backdrop (bowl, dome, etc.). Starlight means pinholes in the backdrop. The mind can grasp finite backdrops; like backstage theatre curtains. If the mind does not resolve the infinite sky in such a way, the idea of night sky can be so big that trying to understand it may be beyond comprehension. Some 'experts' offer this psychology of the mind to help try explain the Moon Illusion. People have tangible concepts of traveling to the horizon. They know approximate sizes of objects en route to the horizon. But the moon is beyond grasp, beyond the horizon, perhaps a bit too much for veridical reconciliation in the mind, and maybe overwhelming enough to cause an anisotropic resolution. Since that earthbound memory can't be 100% complete, the mind has no rock-solid foundation reference points, and thus the size of the moon floats/varies in the mind's eye. If the mind makes such adjustments to accommodate visual input from the eye, input having only incomplete reference anchors, yet the mind frames it in known references to make everything cognitive, then the mind plays tricks of a sort. That can explain illusions. The Moon Illusion could be a trick by the mind to make adjustments to accommodate visual input without having any cognitive contradictions. One of these adjustments or tricks is the "angle of regard". The eye-brain system teams-up to process images of the moon at the horizon as compared to the moon higher in the sky. The horizon offers a frame of reference. The mind can relate to it based on experience and knowledge that the moon is bigger than anything between the eye and the moon's image. But, when the moon is high in the sky, the mind has no experience comparable to its firsthand knowledge of the horizon. The moon is a bright circle in a vast dark sky. The mind lacks reference points or real-life anchors for framing the moon's image. To resolve this cognitive dissonance the mind may cope consciously or subliminally with the sense that the moon is somewhat lost in the vast sky. The impressions are 'small and lost' and 'up there all alone'. Whereas, near the horizon, the moon is a 'big boy' compared to landmarks between the eye and the moon. Meanwhile, nothing physically changed except the angle of the moon in the sky. More Science News about "Blue Refraction" BadAstronomy.com is a website offering an explanation about photons. The sun emits them in every color of the visible light spectrum that people see by using a prism. Blue photons scatter more than others. By comparison, red photons stay together well. Brake lights and red lights are often seen more readily at night than blue or green lights with a blue tint. Red lights are seen better at a distance than green lights are. (Plait. 2008) Blue photons scatter more than all other photons. This accounts for the sky being blue in the daytime. BadAstronomy.com also posits that blue scattering explains why sunsets and sunrises look orange and red. It also explains why moon rise can be red, orange or rust colored when the Moon Illusion is observed. Those color photons stay together better. Meanwhile, the blue photons scatter, bounce off of other matter in the atmosphere and run into even more particulates the closer they get to Earth's surface. Considering all the blue photon diffusion (spreading of light) and collisions with other molecules, it can be postulated that this is another reason why the moon looks bloated and swollen with an orange tint near the horizon. Compared to when the moon is overhead, the eye must see through more atmosphere when the moon is at the horizon. More atmosphere means the blue photons collide with more molecules between the moon and the eye. More collisions mean more diffusion. At the same time, the reddish photons stay more tightly together. The net effects are that moonrise can look ruddy from the red and near-reddish photons, and swollen from the scattered blue photons. As Phil Plait wrote, when photons traverse through the atmosphere from the horizon, then light must push through so much more air before it reaches the eye - compared to when it looks overhead into the much lesser amount of air that the photons traverse. It sounds plausible as a physical explanation for the Moon Illusion. (But note that I'm no physicist, and when I encounter physics, I often learn that there is more to the final explanation than the obvious one that meets the eye.) Summary For good reason the Moon Illusion has mystified humankind throughout the ages. Based on facts known today, the answer is elusive. There are physical and psychological components that surely interplay. As conjectured in the beginning of this paper, the truth probably lies somewhere in-between. Careful consideration combines both physical science and the oft-mysterious workings of the human mind. As a safeguard to preserve cognizance, the mind automatically engages its intellect and emotion to reconcile the Moon Illusion. As with some of life's most challenging puzzles, the Moon Illusion probably has no single "magic answer". The truth is probably partial answers cobbled together. References Berkeley, George. "A Treatise Concerning the Principles of Human Knowledge", page 26, Section 47. [NOTE: This is a compilation of 125+ of Berkeley's essays/writings (circa 1710-1743) called "sections"]. Project Gutenberg On-line Book Catalog. Dates of electronic publication and latest update are unknown (not on webpage or embedded). Accessed on May 5, 2008. http://www.gutenberg.org/catalog/world/readfilefk_files=6354&pageno=26 Hawley, and Smith, Marjorie E. origin date unknown. U.S.A. Department of Energy, Argonne National Laboratory. "Ask A Scientist, Astronomy Archive, Earth-Moon distance." Dates of electronic publication and latest update are unknown (not on webpage or embedded). Division of Educational Programs. Accessed on May 5, 2008. http://www.newton.dep.anl.gov/newton/askasci/1995/astron/AST046.HTM Plait, Phil. "Blue Skies." 2008. BadAstronomy.com. Last modified December 21, 2004. Accessed on May 5, 2008 http://www.badastronomy.com/bad/misc/blue_sky.html SandlotScience.com. "Moon Illusion Demonstration". Tony Azevedo 2000. Artist: R. Ausbourne. SandlotScience.com. Dates of electronic publication and latest update are unknown (not on site or embedded). Accessed May 5, 2008. http://www.sandlotscience.com/Moonillusion/Moon_Illusion_Demo.htm Simanek, Donald E. "The Moon Illusion, An Unsolved Mystery." LHUP.edu. January 11, 2002. Several paragraphs under subheadings about geometry. Lock Haven University of Pennsylvania. Accessed on May 5, 2008. http://www.lhup.edu/dsimanek/3d/moonillu.htm Read More