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 'R' :

Red dwarf : a small, low surface temperature main sequence star. They are quite faint, smaller than our Sun, and evolve very slowly. Red giant : a star of low to intermediate mass in the late stage of its evolution with low temperature hence its colour.

Reflector : a telescope that uses a mirror or a combination of mirrors to gather light.

Refractor : a telescope that uses a lens to gather light.

Retrograde : the motion of one object in reverse motion to the one it orbits. For example most of the planets move in a prograde motion compared to the Sun; that is they orbit the sun in the same direction as the Sun’s rotation. Triton has a retrograde motion compared to Neptune.

Right Ascension (R.A.) : a coordinate used to define the position of an object on the celestial sphere. It's the equivalent of longitude,, and is measured in hours, minutes and seconds.

Resources :

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