The change in the relative positions of objects when they are viewed from different places. The actual angular shift measured when a viewpoint is changed is also described as trigonometric parallax. In the case of astronomical objects, such changes are measurable only for relatively nearby objects in relation to the more distant stars. However, the measurement of parallaxes, where possible, is important since it is one of the most direct methods of determining astronomical distances. In astronomy, the word parallax is often used synonymously with distance. The rotation of the Earth produces a diurnal parallax effect, and the Earth’s orbital motion around the Sun causes annual parallax. See also: statistical parallax.