PAR'ALLAX, n. [Gr. to vary, to decline or wander; beyond, and to change.] In astronomy, the change of place in a heavenly body in consequence of being viewed from different points.
Diurnal parallax, the difference between the place of a celestial body, as seen from the surface, and from the center of the earth, at the same instant.
Annual parallax, the change of place in a heavenly body, in consequence of being viewed at opposite extremities of the earth's orbit.