C
calcium K
A narrow wavelength of blue light which is emitted and absorbed by ions of the element calcium.
caldera
A large, basin-shaped volcanic depression that is more or less circular in form. Most volcanic calderas are produced by collapse of the roof of a magma chamber due to removal of magma by voluminous eruptions or subterranean withdrawal of the magma, although some calderas may be formed by explosive removal of the upper part of a volcano.
carbonate
A compound containing carbon and oxygen; an example is calcium carbonate (limestone).
Cassini, Giovanni Domenico 1625-1712
(Aka Jean Dominique) Italian-born French astronomer. Cassini was the first director of the Royal Observatory in Paris. He discovered four of Saturn's moons (Tethys, Dione, Rhea and Iapetus) and the major gap in its rings.
cataclastic
A texture found in metamorphic rocks in which brittle minerals have been broken, crushed and flattened during shearing.
catena
A chain of craters.
cavus
Hollows, irregular depressions.
central peak
The exposed core of uplifted rocks in complex meteorite impact craters; the central peak material typically shows evidence of intense fracturing, faulting and shock metamorphism.
chaos
A distinctive area of broken terrain.
chasma
A canyon.
chromosphere
The lower level of the solar atmosphere between the photosphere and the corona.
cinders
Loose, vesicular volcanic ejecta 4 to 32 millimeters (.16 to 1.28 inches) in diameter.
cinder cone
A conical hill formed by the accumulation of pyroclastic fragments that fall to the ground in an essentially solid condition.
clast
A fragment of rock that has been transported, either by volcanic or sedimentary processes.
colles
A small hill or knob.
coma
The dust and gas surrounding an active comet's nucleus.
composite volcano
A volcano composed of interbedded lava and pyroclastic material commonly with steep slopes.
convection
Fluid circulation driven by large temperature gradients; the transfer of heat by this automatic circulation (see also Educator's Guide to Convection).
Copernicus, Nicolaus 1473-1543
Polish astronomer who advanced the heliocentric theory that the earth and other planets revolve around the Sun. This was highly controversial at the time; the Ptolemaic view of the universe, which was the prevailing theory for more than 1000 years, was deeply ingrained in the prevailing philosophy and religion.
corona
1) The upper level of the solar atmosphere, characterized by low densities and high temperatures (> 1.0E+06 K); it is not visible from the Earth except during a total eclipse of the sun or by use of special telescopes called coronagraphs. 2) An ovoid-shaped feature.
coronagraph
A special telescope which blocks light from the disk of the Sun in order to study the faint solar atmosphere.
cosmic ray
Electromagnetic rays of extremely high frequency and energy; cosmic rays usually interact with the atoms of the atmosphere before reaching the surface of the Earth. Some cosmic rays come from outside the solar system while others are emitted from the Sun and pass through holes in the corona.
crater
1) A depression formed by the impact of a meteorite. 2) A depression around the orifice of a volcano.
cratons
The relatively stable portions of continents composed of shield areas and platform sediments; typically, cratons are bounded by tectonically active regions characterized by uplift, faulting and volcanic activity.
Cretaceous period
A geological term denoting the interval of Earth history beginning around 144 million years ago and ending 66 million years ago.
Cretaceous-Tertiary boundary
A major stratigraphic boundry on Earth marking the end of the Mesozoic Era, best known as the age of the dinosaurs. The boundary is defined by a global extinction event that caused the abrupt demise of the majority of all life on Earth.
crystalline
Rock types made up of crystals or crystal fragments, such as metamorphic rocks that recrystallized in high temperature or pressure environments, or igneous rocks that formed from cooling of a melt.