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parallax

[par-uh-laks] /ˈpær əˌlæks/
noun
1.
the apparent displacement of an observed object due to a change in the position of the observer.
2.
Astronomy. the apparent angular displacement of a celestial body due to its being observed from the surface instead of from the center of the earth (diurnal parallax or geocentric parallax) or due to its being observed from the earth instead of from the sun (annual parallax or heliocentric parallax)
3.
the difference between the view of an object as seen through the picture-taking lens of a camera and the view as seen through a separate viewfinder.
4.
an apparent change in the position of cross hairs as viewed through a telescope, when the focusing is imperfect.
Origin
1585-1595
1585-95; < Greek parállaxis change, equivalent to parallak- (stem of parallássein to cause to alternate, equivalent to para- para-1 + allássein to vary, akin to állos other; see else, allo-) + -sis -sis
Related forms
parallactic
[par-uh-lak-tik] /ˌpær əˈlæk tɪk/ (Show IPA),
adjective
parallactically, adverb
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for parallactic

parallax

/ˈpærəˌlæks/
noun
1.
an apparent change in the position of an object resulting from a change in position of the observer
2.
(astronomy) the angle subtended at a celestial body, esp a star, by the radius of the earth's orbit. Annual or heliocentric parallax is the apparent displacement of a nearby star resulting from its observation from the earth. Diurnal or geocentric parallax results from the observation of a planet, the sun, or the moon from the surface of the earth
Derived Forms
parallactic (ˌpærəˈlæktɪk) adjective
parallactically, adverb
Word Origin
C17: via French from New Latin parallaxis, from Greek: change, from parallassein to change, from para-1 + allassein to alter
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for parallactic

parallax

n.

1570s, from Middle French parallaxe (mid-16c.), from Greek parallaxis "change, alteration, inclination of two lines meeting at an angle," from parallassein "to alter, make things alternate," from para- (see para- (1)) + allassein "to change," from allos "other" (see alias). Related: Parallactic.

Online Etymology Dictionary, © 2010 Douglas Harper
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parallactic in Medicine

parallax par·al·lax (pār'ə-lāks')
n.
The apparent displacement of an object caused by a change in the position from which it is viewed.


par'al·lac'tic (-lāk'tĭk) adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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parallactic in Science
parallax
  (pār'ə-lāks')   

An apparent shift in the position of an object, such as a star, caused by a change in the observer's position that provides a new line of sight. The parallax of nearby stars caused by observing them from opposite points in Earth's orbit around the Sun is used in estimating the stars' distance from Earth through triangulation.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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