Annual parallax
Parallax Par"al*lax, n. [Gr. ? alternation, the mutual inclination of two lines forming an angle, fr. ? to change a little, go aside, deviate; para` 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. [1913 Webster]

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. [1913 Webster]

3. (Astron.) The annual parallax. See {annual parallax}, below. [PJC]

{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. [1913 Webster]

The Collaborative International Dictionary of English. 2000.

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• annual parallax — noun the parallax of a celestial body using two points in the earth s orbit around the sun as the baseline • Syn: ↑heliocentric parallax • Hypernyms: ↑parallax • Hyponyms: ↑stellar parallax * * * noun …   Useful english dictionary

• annual parallax — metinis paralaksas statusas T sritis fizika atitikmenys: angl. annual parallax; heliocentric parallax vok. heliozentrische Parallaxe, f; Jahresparallaxe, f; jährliche Parallaxe, f rus. гелиоцентрический параллакс, m; годовой параллакс, m pranc.… …   Fizikos terminų žodynas

• annual parallax. — See under parallax (def. 2). * * * …   Universalium

• annual parallax. — See under parallax (def. 2) …   Useful english dictionary

• Parallax — Par al*lax, n. [Gr. ? alternation, the mutual inclination of two lines forming an angle, fr. ? to change a little, go aside, deviate; para beside, beyond + ? to change: cf. F. parallaxe. Cf. {Parallel}.] 1. The apparent displacement, or… …   The Collaborative International Dictionary of English

• Parallax of the cross wires — Parallax Par al*lax, n. [Gr. ? alternation, the mutual inclination of two lines forming an angle, fr. ? to change a little, go aside, deviate; para beside, beyond + ? to change: cf. F. parallaxe. Cf. {Parallel}.] 1. The apparent displacement, or… …   The Collaborative International Dictionary of English

• parallax second — par al*lax sec ond, n. An {annual parallax} of one second of an arc; applied to celestial objects outside the solar system. It is used to measure the distance of an astronomical object from the Earth. A star which has an annual parallax of one… …   The Collaborative International Dictionary of English

• parallax — [par′ə laks΄] n. [Fr parallaxe < Gr parallaxis < parallassein, to vary, decline, wander < para ,PARA 1 + allassein, to change < allos, other: see ELSE] 1. the apparent change in the position of an object resulting from the change in… …   English World dictionary

• Parallax — For other uses, see Parallax (disambiguation). A simplified illustration of the parallax of an object against a distant background due to a perspective shift. When viewed from Viewpoint A , the object appears to be in front of the blue square.… …   Wikipedia

• parallax — parallactic /par euh lak tik/, adj. parallactically, adv. /par euh laks /, n. 1. the apparent displacement of an observed object due to a change in the position of the observer. 2. Astron. the apparent angular displacement of a celestial body due …   Universalium