Astronomy: Conjunction and Opposition

When two Solar System bodies straddle Earth they are said to be in opposition, and when they are in line with Earth they are said to be in conjunction. The Sun and Earth always lie on the ecliptic plane. During Earth’s orbit, the Moon sometimes comes close to the ecliptic plane. When it is between the Sun and Earth (conjunction) there will be an eclipse of the Sun, and when it is on the side of Earth remote from the Sun (opposition) there will be an eclipse of the Moon; hence the name ‘ecliptic’. A heliacal setting is the last visible sighting of a celestial object in the evening sky before its conjunction with the Sun, and a heliacal rising is the first visible sighting of a celestial object in the morning sky after the conjunction.