An inferior conjunction occurs when a Solar System body lies along a straight line between the Earth and the Sun. At this point, the elongation is zero degrees, and the body will have the same right ascension on the celestial sphere as the Sun.

Only the inferior planets, and asteroids or comets which have part or all of their orbits between the Sun and the Earth, can undergo an inferior conjunction.

A planet at inferior conjunction, on a line between the Earth and the Sun.