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astronomical refraction

noun, Astronomy.
refraction (def 3).


[ri-frak-shuh n] /rɪˈfræk ʃən/
Physics. the change of direction of a ray of light, sound, heat, or the like, in passing obliquely from one medium into another in which its wave velocity is different.
  1. the ability of the eye to refract light that enters it so as to form an image on the retina.
  2. the determining of the refractive condition of the eye.
  1. Also called astronomical refraction. the amount, in angular measure, by which the altitude of a celestial body is increased by the refraction of its light in the earth's atmosphere, being zero at the zenith and a maximum at the horizon.
  2. the observed altered location, as seen from the earth, of another planet or the like due to diffraction by the atmosphere.
Origin of refraction
First recorded in 1570-80, refraction is from the Late Latin word refrāctiōn- (stem of refrāctiō). See refract, -ion
Related forms
refractional, adjective
nonrefraction, noun
nonrefractional, adjective
Can be confused Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for astronomical-refraction


(physics) the change in direction of a propagating wave, such as light or sound, in passing from one medium to another in which it has a different velocity
the amount by which a wave is refracted
the ability of the eye to refract light
the determination of the refractive condition of the eye
(astronomy) the apparent elevation in position of a celestial body resulting from the refraction of light by the earth's atmosphere
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin and History for astronomical-refraction



1570s, from Late Latin refractionem (nominative refractio) "a breaking up," noun of action from past participle stem of Latin refringere "to break up," from re- "back" (see re-) + comb. form of frangere "to break" (see fraction).

Online Etymology Dictionary, © 2010 Douglas Harper
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astronomical-refraction in Medicine

refraction re·frac·tion (rĭ-frāk'shən)

  1. The turning or bending of any wave, such as a light or sound wave, when it passes from one medium into another of different density.

  2. The ability of the eye to bend light so that an image is focused on the retina.

  3. Determination of the refractive characteristics of the eye and often the correction of refractive defects with lenses. Also called refringence.

re·frac'tion·al or re·frac'tive adj.
re·frac'tive·ness or re'frac·tiv'i·ty (rē'frāk-tĭv'ĭ-tē) n.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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astronomical-refraction in Science

  1. The bending of a wave, such as a light or sound wave, as it passes from one medium to another medium of different density. The change in the angle of propagation depends on the difference between the index of refraction of the original medium and the medium entered by the wave, as well as on the frequency of the wave. Compare reflection. See also lens, wave.

  2. The apparent change in position of a celestial body caused by the bending of light as it enters the Earth's atmosphere.

Our Living Language  : The terms refraction and reflection describe two ways that waves, as of sound or light, change course upon encountering a boundary between two media. The media might consist of two different substances, such as glass and air, or a single substance in different states in different regions, such as air at different temperatures or densities in different layers. Reflection occurs, as in a mirror, when a wave encounters the boundary but does not pass into the second medium, instead immediately changing course and returning to the original medium, typically reflecting from the surface at the same angle at which it contacted it. Refraction occurs, as in a lens, when a wave passes from one medium into the second, deviating from the straight path it otherwise would have taken. The amount of deviation or "bending" depends on the indexes of refraction of each medium, determined by the relative speed of the wave in the two media. Waves entering a medium with a higher index of refraction are slowed, leaving the boundary and entering the second medium at a greater angle than the incident wave. Waves entering a medium with a lower index are accelerated and leave the boundary and enter the second medium at a lesser angle. Incident light waves tend to be fully reflected from a boundary met at a shallow angle; at a certain critical angle and at greater angles, some of the light is also refracted; looking at the surface of water from a boat, for instance, one can see down into the water only out to where the sight line reaches the critical angle with the surface. Light passing through a prism is mostly refracted, or bent, both when it enters the prism and again when it leaves the prism. Since the index of refraction in most substances depends on the frequency of the wave, light of different colors is refracted by different amounts—hence the colorful rainbow effect of prisms. The boundary between media does not have to be abrupt for reflection or refraction to occur. On a hot day, the air directly over the surface of an asphalt road is warmer than the air higher up. Light travels more quickly in the lower region, so light coming down from the sky (from not too steep an angle) is refracted back up again, giving a "blue puddle" appearance to the asphalt—a mirage.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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astronomical-refraction in Culture

refraction definition

A change of direction that light undergoes when it enters a medium with a different density from the one through which it has been traveling — for example, when, after moving through air, it passes through a prism. (Compare reflection.)

Note: Lenses and other optical instruments work through refraction of light.
The New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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