Free Astronomy Quiz

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  2. Terminology - C

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 'C' :



Celestial sphere : an imaginary sphere around the Earth used to determine the position of objects in the sky.

Cepheid : variable star used to measure the distance of galaxies or star clusters. Cepheid variable stars change their brightness at regular intervals and therefore are highly predicable. By observing them we can determine their apparent magnitude, compare that to their absolute magnitude, and determine distance.

Charge-Coupled Device (CCD) : an imaging device used in most areas of astronomy. Its movement of electrical charges can then be converted to digital values to build images.

Chromosphere : part of the Sun's atmosphere, it is the second most outer layer which is a few thousand kilometers thick. It has a low density and is fairly transparent; however it is visible during total solar eclipses.

Circumpolar star : a star near a celestial pole which can be observed all year round as it never dips below the horizon.

Clusters : a group of stars, clouds or galaxies held together by their gravity.

Collimation : adjusting the line of sight of a telescope by aligning the optical elements so that they point in the same direction. This is done to improve the performance of a telescope and by using a collimator.

Color index : a numerical measure looking at the color of an astronomical object in order to determine its temperature.

Coma : as a comet approaches the Sun, it develops a cometary coma around the nucleus. It is a hazy patch of gas and dust around the comet.

Comet : a small astronomical object made of ice and rocky debris which orbits the Sun in a highly eccentric orbit. As it approaches the Sun in its orbit, the ice in the nucleus evaporates and forms a coma and a tail.

Conjunction : when two astronomical objects have the same right ascension. This means that they all lie in a straight line, as seen from Earth.

Constellation : a grouping of stars forming a recognizable patter in the sky. The stars are not part of a group as they are usually at various distances from each other. There are 88 recognized constellations.

Corona : part of the Sun's atmosphere, it is the outermost layer.

Cosmic rays : subatomic particles traveling at high speed in space.

Cosmology : the study of the formation, evolution and future of the universe.

Culmination : when an astronomical object crosses the meridian above an observer.




Resources :


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


  • Articles - Alongside the quizzes, you'll find short articles on related topics, to help widen your knowledge of that area.

  • Calendar - Our calendar will let you keep up to date with what's happening in the night sky, and with many space mission events

  • Glossary - As with any field of scientific study astronomy has a long list of important terminology. So we've put together a glossary where you can check you fully understand the meaning of the more unusual words!