conjunction

conjunction in astronomy, alignment of two celestial bodies as seen from the earth. Conjunction of the moon and the planets is often determined by reference to the sun. When a body is in conjunction with the sun, it rises with the sun, and thus cannot be seen; its elongation is 0°. The moon is in conjunction with the sun when it is new; if the conjunction is perfect, an eclipse of the sun will occur. Mercury and Venus, the two inferior planets, have two positions of conjunction. When either lies directly between the earth and the sun, it is in inferior conjunction; when either lies on the far side of the sun from the earth, it is in superior conjunction.

conjunction The occasion when two Solar System bodies have the same celestial longitude as seen from Earth; the bodies may be a planet and the Sun, two planets, or the Moon and a planet. Superior planets (i.e. those with orbits outside that of the Earth) are at conjunction when they lie directly behind the Sun as seen from Earth. Mercury and Venus, which are closer to the Sun, have two conjunctions; inferior conjunction, when they lie between the Earth and Sun; and superior conjunction, when they lie on the far side of the Sun.