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Definition of parallax - 7 dictionary results

par⋅al⋅lax

  [par-uh-laks]
Use parallax in a Sentence
–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). Compare parallactic ellipse.
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:
1585–95; < Gk parállaxis change, equiv. to parallak- (s. of parallássein to cause to alternate, equiv. to para- para- 1 + allássein to vary, akin to állos other; see else, allo- ) + -sis -sis

Related forms:
par⋅al⋅lac⋅tic  [par-uh-lak-tik] , adjective
par⋅al⋅lac⋅ti⋅cal⋅ly, adverb
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2009.
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par·al·lax   (pār'ə-lāks')   


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n.  An apparent change in the direction of an object, caused by a change in observational position that provides a new line of sight.

[French parallaxe, from Greek parallaxis, from parallassein, to change : para-, among; see para-1 + allassein, to exchange (from allos, other; see al-1 in Indo-European roots).]
par'al·lac'tic (-lāk'tĭk) adj.
The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2009 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Parallax

Par"al*lax\, n. [Gr. ? alternation, the mutual inclination of two lines forming an angle, fr. ? to change a little, go aside, deviate; ? beside, beyond + ? to change: cf. F. parallaxe. Cf. Parallel.]

1. The apparent displacement, or difference of position, of an object, as seen from two different stations, or points of view.

2. (Astron.) The apparent difference in position of a body (as the sun, or a star) as seen from some point on the earth's surface, and as seen from some other conventional point, as the earth's center or the sun.

Annual parallax, the greatest value of the heliocentric parallax, or the greatest annual apparent change of place of a body as seen from the earth and sun; as, the annual parallax of a fixed star.

Binocular parallax, the apparent difference in position of an object as seen separately by one eye, and then by the other, the head remaining unmoved.

Diurnal, or Geocentric, parallax, the parallax of a body with reference to the earth's center. This is the kind of parallax that is generally understood when the term is used without qualification.

Heliocentric parallax, the parallax of a body with reference to the sun, or the angle subtended at the body by lines drawn from it to the earth and sun; as, the heliocentric parallax of a planet.

Horizontal parallax, the geocentric parallx of a heavenly body when in the horizon, or the angle subtended at the body by the earth's radius.

Optical parallax, the apparent displacement in position undergone by an object when viewed by either eye singly. --Brande & C.

Parallax of the cross wires (of an optical instrument), their apparent displacement when the eye changes its position, caused by their not being exactly in the focus of the object glass.

Stellar parallax, the annual parallax of a fixed star.
Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.
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parallax 
1580, from M.Fr. parallaxe (1557), from Gk. parallaxis "change, alteration, inclination of two lines meeting at an angle," from parallassein "to alter, make things alternate," from para- "beside" + allassein "to change," from allos "other" (see alias).
Online Etymology Dictionary, © 2001 Douglas Harper
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Main Entry: par·al·lax
Pronunciation: 'par-&-"laks
Function: noun
: the apparent displacement or the difference in apparent direction of anobject as seen from two different points not on a straight line with the object 1/4 inches apart; yet the small parallax causedby the slightly different angle of vision enables us to see three-dimensional, plastic images and to judge distances accurately —Erwin Raisz>
Merriam-Webster's Medical Dictionary, © 2002 Merriam-Webster, Inc.
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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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parallax   (pār'ə-lāks')  Pronunciation Key 


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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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