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Webster 1913 Edition


Parallax

Par′al-lax

,
Noun.
[Gr. [GREEK] alternation, the mutual inclination of two lines forming an angle, fr. [GREEK] to change a little, go aside, deviate;
παρά
beside, beyond + [GREEK] 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; it is equivalent to the parallax of an astronomical object which would be observed by taking observations of the object at two different points one astronomical unit (the distance of the Earth from the sun) apart, if the line joining the two observing points is perpendicular to the direction to the observed object;
as, the
annual parallax
of a fixed star
. The distance of an astronomical object from the Earth is inversely proportional to the
annual parallax
. A star which has an annual parallax of one second of an arc is considered to be one parsec (3.26 light years) distant from the earth; a star with an annual parallax of one-hundredth second of an arc is 326 light years distant. See
parsec
in the vocabulary, and
stellar parallax
, below.
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 parallax
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 1828 Edition


Parallax

PAR'ALLAX

,
Noun.
[Gr. to vary, to decline or wander; beyond, and to change.] In astronomy, the change of place in a heavenly body in consequence of being viewed from different points.
Diurnal parallax, the difference between the place of a celestial body, as seen from the surface, and from the center of the earth, at the same instant.
Annual parallax, the change of place in a heavenly body, in consequence of being viewed at opposite extremities of the earth's orbit.

Definition 2024


parallax

parallax

English

Noun

parallax (plural parallaxes)

  1. An apparent shift in the position of two stationary objects relative to each other as viewed by an observer, due to a change in observer position.
    • 2008, Bernard Perron, ‎Mark J. P. Wolf, The Video Game Theory Reader 2 (page 157)
      Planes farther back on the z-axis scroll more slowly than those in front of them, producing a parallax effect. Early games with parallax scrolling tended to have their action taking place all in the forefront plane []
  2. The angle of seeing of the astronomical unit.

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