C

Cardinal points

The four principal points of the compass: north, south, east, and west.

 

Cassegrain focus

A telescope arrangement in which a convex hyperboloidal secondary mirror reflects the beam back through an opening in the primary mirror, where the image is formed and viewed. Since the image is formed at the back of the telescope, it is easier to mount and use equipment.

 

Cassini division

The 4800 km (3000 mi) gap between the outer and the middle ring of saturn.

 

Celestial equator

The projection of the earth's equator on tha celestial sphere. It is a great circle whose points are 90^o from the north and south celestial poles.

 

Celestial horizon

The great circle on the celestial sphere whose points are 90o from the zenith and nadir.

 

Celestial mechanics

A branch of astronomy that deals with the gravitation and motion of bodies in space.

 

Celestial meridian

The great circle on the celestial sphere that passes through the zenith and nadir and crosses the observer's horizon at 90^o.

 

Celestial poles

The points on the celestial sphere established by the extension of the earth's axis of rotation.

 

Celestial sphere

An apparent sphere of infinite radius at whose center the observer is located and on whose surface the celestial bodies appear to be located.

 

Center of mass (center of gravity)

One point in a single body or within a system of several bodies that remains fixed or moves uniformly through space as through the entire mass of the body or system were concentrated at that point.

 

Centrifugal force

A term used to describe the resistance of a particle to being accelerated along a curved path.

 

Centripetal force

A center-directed force which diverts a body from a straight-line path into a curved path.

 

Cepheid variable

A yellow giant or supergiant pulsating star whose brigthness varies because it expands and contracts periodically.

 

Ceres

The first and largest asteroid (minor planet) discovered.

 

Chromatic aberration

The failure of a simple lens to bring visible light to a single focus because it refracts the wavelengths of visible light differently, producing a dispersion.

 

Chromosphere

The nearly transparent, hot layer of the sun's atmosphere that lies directly above the solar visible surface, or photosphere.

 

Circumpolar star

Stars whose angular distances from the north or south celestial poles are less than the latitude of the observer, so that they always remain above the horizon.

 

Cluster of stars

A group of stars with a common region, bound together by mutual gravitation, and moving in space along nearly parallel paths at about the same speed.

 

Cluster variables

A class of high-velocity pulsating stars (RR Lyrae stars) with period of less than one day. They are very numerous in the Milky Way and in globular clusters.

 

Coelostat

An instrument that permit the sun's image to be viewed in a fixed positon throughout the day. This is accomplished by use of a telescope with an equatorially mounted, clock-driven plane mirrror that follows the sun and a fixed mirror that directs the sunlight to the objective of a fixed tower telescope.

 

Collimator

A lens system that renders a diverging beam of light into parallel beam.

 

Color index

The different between the photographic and photovisual magnitudes of a star. C.I.= m_pg - m_pv.

 

Comparison spectrum

The spectrum of a vaporized element (often iron) photographed next to a stellar spectrum for comparison and identification of their spectral line.

 

Coma (comet)

The diffuse gaseous shell around the nucleus. The nucleus and coma comprise the head of the comet.

 

Coma (optical)

An optical defect in which light rays that strike a lens or mirror at an angle to its axis are not focused at the same place.

 

Configuration

A special orientation of a planet or the moon with respect to the sun.

 

Conjunction

A configuration of two or more celestial bodies that are in line longitudinally and have the same right ascension.

 

Constellation

A configuration of stars with which the ancients associated the name and shape of a person, animal, or object in their mythology. Today, it designates the definite are in the sky in which the configuration is located.

 

Continuous spectrum

The spectrum of light that appears as a continuous blend of colors emitted by an incandescent solid, liquid, or gas under pressure.

 

Coordinates

Angular distances that are used to locate points on the terrestrial sphere (longitude and latitude) and positions of celestial bodies on the celestial sphere (right ascension and declination).

 

Core

The central part of any celestial body.

 

Coriolis effect

The deflection with respect to the earth's surface of a moving body, air, or water, due to the earth's rotation. The deflection is to the right in the northern hemisphere and to the left in the southern hemisphere.

 

Corona

The tenuous outer layer of the sun's atmosphere that is visible during a total solar eclipse or with a coronagraph.

 

Coronagraph

An instrument for photographing the sun's corona whenever the sun is visible.

 

Corpuscolar radiation

Charged particles, such as atomic nuclei and electrons. The solar wind and cosmis rays are sometimes so termed.

 

Cosmic rays

High energy particles (mostly protons) from space that strike the earth's atmosphere and produce secondary particles. They are believed to originate in supernova explosions, although some are produced in solar flares.

 

Cosmogony

The study of the creation and evolution of the universe.

 

Cosmological principle

The assumption that the universe at any time is the same from any position and in any direction.

 

Cosmology

The study of design, character, and extent of the universe.

 

Coude focus

A secondary optical system in a reflecting telescope that directs the reflected light down the telescope's polar axis to a focus that remains fixed regardless of any movement of the telescope.