# quadrature

quadrature, in astronomy, arrangement of two celestial bodies at right angles to each other as viewed from a reference point. If the reference point is the earth and the sun is one of the bodies, a planet is in quadrature when its elongation is 90°. As viewed from the earth, the half-moon is in quadrature to the sun. The inferior planets (Mercury and Venus) never reach quadrature; the superior planets each have two points of quadrature in their orbits.

*The Columbia Electronic Encyclopedia,* 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

#### More on *quadrature* from Fact Monster:

- elongation - elongation elongation, in astronomy, the angular distance between two points in the sky as measured ...
- John Wallis - Wallis, John Wallis, John , 1616–1703, English mathematician. He was Savilian professor of ...
- phase, in astronomy - phase phase, in astronomy, the measure of how much of the illuminated surface of a planet or ...
- geometric problems of antiquity - geometric problems of antiquity geometric problems of antiquity, three famous problems involving ...
- Archimedes - Archimedes Archimedes , 287–212 B.C., Greek mathematician, physicist, and inventor. He is ...