par|al|lax

par|al|lax «PAR uh laks», noun.

1. the apparent change in the position of an object when it is seen or photographed from two different points which are not on a direct line with the object. Parallax is used in surveying to determine distances of objects.

2. Astronomy. the angle between the straight lines that join a heavenly body to two different points of observation, equal to the difference in the directions in which the body is seen from the two points. See also annual parallax (Cf. ↑annual parallax), diurnal parallax. (Cf. ↑diurnal parallax)

3. Photography. the difference between what the viewfinder shows and what the lens records on a film.

4. an apparent shifting of the cross hairs of a telescope, caused by imperfect focusing.

╂[< Greek parállaxis change, alternation, < parallássein to alter < para- beside + allássein to change < állos other]