Definitions for: Parallax


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



Webster (1913) Definition: 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.

See Also: annual parallax, diurnal parallax, geocentric parallax, heliocentric parallax, optical phenomenon


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