As with any field of scientific study, astronomy has a long list of important terminology. So we've put together this glossary where you can check you fully understand the meaning of the common terms, as well as some of the more unusual words.

A -- B -- C -- D -- E -- F -- G -- H -- I -- J -- K -- L -- M -- N -- O -- P -- Q -- R -- S -- T -- U -- V -- W -- X -- Y -- Z

Words beginning with 'O' :

Objective : the light gathering element of a telescope. It’s a lens in a refractor and a mirror in a reflector. A telescope’s main light-gathering lens or mirror.

Occultation : when an astronomical object passes directly in front of another object.

Opposition : when a planet, comet or asteroid is directly opposite the Sun with the Earth in between.

Orbit : the path taken by an astronomical object which can be calculated if the masses and separation of the objects are known. The path is usually repeated and follow Kepler’s laws of planetary motion.

Orbital speed : the speed at which an astronomical object orbits the center of mass of a system. It is usually around another (usually more massive) object.

Resources :

To support the quizzes in each section, we've put together some extra resources to provide further information: