opposition
From Glossary of Meteorology
In astronomy, the arrangement of the earth, sun, and one of the other planets or the moon, in which the angle subtended at the earth between the sun and the third body, in the plane of the ecliptic, is 180°.
When this is the case, a superior planet is on the opposite side of the earth from the sun and is most easily observed.
Compare conjunction, quadrature.
