from The American Heritage® Dictionary of the English Language, 4th Edition

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

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The change of angular position of two stationary points relative to each other as seen by an observer, due to the motion of an observer.
  • n. The apparent shift of an object against a background due to a change in observer position.
  • n. The angle of seeing of the astronomical unit.

from the GNU version of the Collaborative International Dictionary of English

  • n. The apparent displacement, or difference of position, of an object, as seen from two different stations, or points of view.
  • n. 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.
  • n. The annual parallax. See annual parallax, below.

from The Century Dictionary and Cyclopedia

  • n. An apparent displacement of an object observed, due to real displacement of the observer, so that the direction of the former with reference to the latter is changed.
  • n. In optics, an apparent shifting of the spider-lines in a telescope-reticle as the eye is moved before the eyepiece: it is due to the non-coincidence of the threads with the focal plane of the object-glass.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. the apparent displacement of an object as seen from two different points that are not on a line with the object


from The American Heritage® Dictionary of the English Language, 4th Edition

French parallaxe, from Greek parallaxis, from parallassein, to change : para-, among; see para-1 + allassein, to exchange (from allos, other).


  • "Do not let us fear," wrote Lalande in his _Astronomie des Dames_, "do not let us fear to use the term parallax, despite its scientific aspect; it is convenient, and this term explains a very simple and very familiar effect."

    Astronomy for Amateurs

  • I get the impression the author in the last link should have actually read the Wikipedia article he linked to, because what he calls parallax it calls stereopsis.

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  • The term parallax proving “caviare to the general,” they further explained that it meant the angle formed by the inclination of two straight lines drawn from either extremity of the earth’s radius to the moon.

    From the Earth to the Moon

  • If they do, the parallax is not set for the range of the target you are using.

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  • Not to mention that a fixed 10 power scope with no adjustable parallax is problematic at best, in an urban combat environment.

    Marines Get New Sniper Scope

  • They were as much puzzled about the meaning of the word parallax as I had been with regard to the word algebra, and only learnt what it meant when Brewster went to study for the kirk in Edinburgh.

    Personal Recollections, from Early Life to Old Age, of Mary Somerville

  • To be able to do this, astronomers have developed what's known as parallax, which is then used to calibrate distance indicators for objects further away, which are then used to calibrate even further objects, etc ....

    Angry Astronomer

  • All the planets have disappeared, the moon’s phases are screwy, and the sun’s parallax is too large.

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  • If that doesn’t impress you, consider the vertical and horizontal parallax is so smooth and perfect you’ll be able to walk around the setup and swear you could reach out and touch it.

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  • One method uses what is known as a parallax barrier in front of a conventional liquid-crystal display screen, a layer of material with precisely placed slits that allow each eye to see a different set of pixels on the display.

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  • par all ax

    November 21, 2013

  • Super-important in astronomy...and target practice with your .22!

    January 4, 2007