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; ? beside, beyond + ? to change: cf. F. parallaxe. Cf. .] 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.
, 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.
, the apparent difference in position of an object as seen separately by one eye, and then by the other, the head remaining unmoved.
, or , , 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.
, 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.
, the geocentric parallx of a heavenly body when in the horizon, or the angle subtended at the body by the earth's radius.
, the apparent displacement in position undergone by an object when viewed by either eye singly. -Brande & C.
(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.
, the annual parallax of a fixed star.