Astronomy & telescopes glossary - C

Astronomy & Telescopes Glossary - C

Catadioptric telescope - A telescope that uses both lenses and mirrors to form an image. Common catadioptric telescopes include Schmidt-Cassegrain and Schmidt-Maksutov telescopes.

Cassegrain telescope - A wide-angle reflecting telescope with a concave mirror that receives light and focuses the image. A second mirror reflects the light through a gap in the primary mirror, allowing the eyepiece or camera to be mounted at the back end of the tube.

Cassini Division - The main division between Saturn's largest rings (A and B rings).

Cassini-Huygens mission - The NASA Cassini-Huygens spacecraft was launched on October 1997 and arrived at Saturn in 2006.

CCD - Abbreviation for charge-coupled device, which is a semiconductor chip found in digital cameras that takes the place of film.

Celestial coordinates - Pairs of numbers (right ascension and declination) used to locate celestial objects. They are similar to longitude and latitude on Earth.

Celestial sphere - All celestial bodies are assigned a two-dimensional coordinate location on the surface of this imaginary sphere.

Chromatic aberration - A type of distortion in lenses whereby the lens will bend light of different colors by unequal amounts. A well-made lens reduces this problem.

Chromosphere - The inner layer in the Sun's atmosphere between the photosphere and the corona. The chromosphere is visible during a total solar eclipse.

Cislunar - The space between the Earth and the orbit of the Moon.

Coated optics - An antireflection coating in lenses and mirrors.

Collimation - The process of aligning the optics of a reflector telescope.

Coma - The gas cloud that surrounds the nucleus of a comet.

Comet - A celestial body that orbits around the sun that is made up of frozen ice, gas and dust. A comet becomes visible when it gets closer to the Sun.

Compound telescope - A telescope in which a secondary mirror makes a change in the focal length. Compound telescopes include Schmidt-Cassegrain and Schmidt-Maksutov telescopes.

Conjunction - A planet is in conjunction when the Sun is exactly between the planet and the Earth or when a planet, the Sun, and the Earth are lined up.

Constellation - A group of stars that form a pattern as seen from the Earth. There are 88 constellations.

Corona - The top layer of the sun's atmosphere. During a complete solar eclipse, the corona is visible.

Crepe ring - The Crêpe ring, or C ring, is the inner ring of Saturn's three major rings. It is visible in small telescopes.

Crescent moon - A moon that is between a half moon and a new moon.