Geocentric 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.

### Look at other dictionaries:

• geocentric parallax — noun the parallax of a celestial body using two points on the surface of the earth as the earth rotates • Syn: ↑diurnal parallax • Hypernyms: ↑parallax • Hyponyms: ↑horizontal parallax, ↑solar parallax * * * noun …   Useful english dictionary

• geocentric parallax — parinis paralaksas statusas T sritis fizika atitikmenys: angl. diurnal parallax; geocentric parallax vok. Tagesparallaxe, f rus. суточный параллакс, m pranc. parallaxe diurne, f …   Fizikos terminų žodynas

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

• geocentric parallax — /dʒioʊˌsɛntrɪk ˈpærəlæks/ (say jeeoh.sentrik paruhlaks) noun See parallax (def. 2) …   Australian English dictionary

• geocentric 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 — [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 — 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

• parallax — /ˈpærəlæks / (say paruhlaks) noun 1. a misalignment in the comparison of two locations due to the relative position of the observer. 2. diurnal parallax or geocentric parallax, the apparent displacement of a heavenly body due to its being… …   Australian English dictionary