Quadrature (astronomy)
In spherical astronomy, quadrature is the configuration of a celestial object in which its elongation is perpendicular to the direction of the Sun. It is applied especially to the position of a superior planet or the Moon at its first and last quarter phases.
As shown in the diagram above, a planet can be at the western quadrature or at the eastern quadrature. Note that an inferior planet can never be at quadrature to the reference planet.
