Atmospheric Optics
Light is all around us, from both natural and artificial sources, during the day and the night. We think we understand it, and that what we see by it is an exact representation of what we are looking at. However we can be mistaken; the setting sun seen on the horizon has in fact already dropped below the horizon. Twinkling stars are also an effect of this same process, called refraction.
Light passing through a medium such as air or water can be absorbed and scattered by the molecules in the medium or refracted by changes in air density. Earth's atmosphere contains air, water and dust molecules that cause light rays from the sun to change direction as they pass through slightly different densities of air - this is known as refraction. The amount of refraction of light is dependent on the refractive index (a measure of how much a substance bends light, dependent on its density and the type of molecules) and the incident angle at which the light enters the substance. Denser substances such as water will bend the light more than a less dense substance like air, and light entering a substance at an angle will refract more than entering perpendicular to the substance's surface. Air itself can have different indices- air that is warm will be less dense and so will refract light less.
Looking up in the direction of the zenith, an observer will look through one air mass- ie the minimum amount of air that light from the sun will travel through to the surface. Light at an angle z from the zenith will pass through more air, so travels through an equivalently greater air mass at a greater incidence angle z. Roughly, the air mass varies with secant z,
as cos(z)=1 airmass / n airmasses in a first-order case,
although...
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...ed at the same time. There is also a chance that light from another point on the disk would be refracted into the line-of-sight so the intensity of light would not change.
An observer, therefore, can only be sure that what he is looking at is a true representation of an object if he is looking straight up to the zenith. Any view towards the horizon will be subject to increasing refractive and scattering effects, that can cause disparity in an object's position, changes in the colour of the incoming light and minute changes in the quality of light causing twinkling.
Sources:
David K Lynch and William Livingston; Color and Light in Nature, Cambridge University Press, 2nd Ed. 2001
Fraknoi, Morrison, Wolff; Voyages through the Universe, Saunders College Publishing, 2nd Ed. 2000
Scientific American: Ask The Experts
Astronomy Picture of the Day: Why Stars Twinkle
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Newton, Henry, and William Winsor. "Spotlight on Colour: Flake White." Winsor&Newton. N.p., 2011. Web. 30 Apr. 2014.
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Refraction is what happens to light when it passes from one medium to another. For example, things appear differently from the bottom of a swimming pool than on the top. Simplistically, refraction is the bending of light. The explanation for this phenomenon, however, can be described with light as rays and light as waves. No matter the case, it is important to remember that the speed of light is constant in every homogeneous medium, regardless of shape, size or form.
The optical lenses of the eyes are used to focus light. The light that penetrates the lens is controlled by the iris, which constricts and dilates in response to varying light conditions. Controlling the amount of light that reaches the lens, and subsequently the photoreceptors in the pigmented retina, is not enough to adequately discern images in three dimensions. The lens is therefore responsible for adjusting to conditions based on how far away or near an object is that is being viewed. To view something relatively close, the lens is bent to form a more spherical shape by the ciliary body muscles. Likewise, to view further distanced objects, the lens must undergo accommodation
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Refraction of Light Aim: To find a relationship between the angles of incidence and the angles of refraction by obtaining a set of readings for the angles of incidence and refraction as a light ray passes from air into perspex. Introduction: Refraction is the bending of a wave when it enters a medium where it's speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media and is described quantitatively by Snell's Law. (Refer to diagram below)
Klosowski, John E. "The Color Purple and Its True Color." Houston Cronicle. December 14, 1995 : 42-44.
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which can be up to 100ft high. The sun was now beginning to set. It
atmosphere. If there is more carbon dioxide in the atmosphere more rays from the sun are