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C

Caldera
A type of volcanic crater that is extremely large, usually formed by the collapse of a volcanic cone or by a violent volcanic explosion. Crater Lake is one example of a caldera on Earth.

Catena
A series or chain of craters.

Cavus
A hollow, irregular depression.

Celestial Equator
An imaginary line that divides the celestial sphere into a northern and southern hemisphere.

Celestial Poles
The North and South poles of the celestial sphere.

Celestial Sphere
An imaginary sphere around the Earth on which the stars and planets appear to be positioned.

Cepheid Variable
This is a variable star whose light pulsates in a regular cycle. The period of fluctuation is linked to the brightness of the star. Brighter Cepheids will have a longer period.

Chaos
A distinctive area of broken terrain.

Chasma
Another name used to describe a canyon.

Chondrite
A meteorite that contains chondrules.

Chondrule
Small, glassy spheres commonly found in meteorites.

Chromosphere
The part of the Sun's atmosphere just above the surface.

Circumpolar Star
A star that never sets but always stays above the horizon. This depends on the location of the observer. The further South you go the fewer stars will be circumpolar. Polaris, the North Star, is circumpolar in most of the northern hemisphere.

Circumstellar Disk
A torus or ring-shaped accumulation of gas, dust, or other debris in orbit around a star in different phases of its life cycle.

Coma
An area of dust or gas surrounding the nucleus of a comet.

Comet
A gigantic ball of ice and rock that orbit the Sun in a highly eccentric orbit. Some comets have an orbit that brings them close to the Sun where they form a long tail of gas and dust as they are heated by the Sun's rays.
Cosmic Ray
Conjunction
An event that occurs when two or more celestial objects appear close close together in the sky.

Constellation
A grouping of stars that make an imaginary picture in the sky.

Corona
The outer part of the Sun's atmosphere. The corona is visible from Earth during a total solar eclipse. It is the bright glow seen in most solar eclipse photos.


Cosmic String
A tube-like configuration of energy that is believed to have existed in the early universe. A cosmic string would have a thickness smaller than a trillionth of an inch but its length would extend from one end of the visible universe to the other.

Cosmogony
The study of celestial systems, including the Solar System, stars, galaxies, and galactic clusters.

Cosmology
A branch of science that deals with studying the origin, structure, and nature of the universe.

Crater
A bowl-shaped depression formed by the impact of an asteroid or meteoroid. Also the depression around the opening of a volcano.

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