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Words begining with "C"


Act of comparing an instrument's measuring accuracy to a known standard.


The amount of heat needed to raise the temperature of one gram of water at 15 degrees centigrade one degree centigrade. Compare with British Thermal Unit.


A man-made watercourse designed to carry qoods or water.


The layer formed naturally by the leaves and branches of trees and plants.


A large but narrow gorge with deep sides.

Cape (or Point)

A piece of land extendinq into water.

Carbon Cycle

All parts (reservoirs) and fluxes of carbon. The cycle is usually thought of as four main reservoirs of carbon interconnected by pathways of exchange. The reservoirs are the atmosphere, terrestrial biosphere (usually includes freshwater systems), oceans, and sediments (includes fossil fuels). The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological, and biological processes. The ocean contains the largest pool of carbon near the surface of the Earth, but most of that pool is not involved with rapid exchange with the atmosphere.

Carbon Dioxide (CO2)

A minor but very important component of the atmosphere, carbon dioxide traps infrared radiation. Atmospheric CO2 has increased about 25 percent since the early 1800s, with an estimated increase of 10 percent since 1958 (burning fossil fuels is the leading cause of increased CO2, deforestation the second major cause). The increased amounts of CO2 in the atmosphere enhance the greenhouse effect, blocking heat from escaping into space and contributing to the warming of Earth's lower atmosphere.


Radio frequency capable of being modulated with some type of information. See modulation.

Carrying Capacity

The steady-state density of a given species that a particular habitat can support.

Catalog Number

A five-digit number assigned to a cataloged orbiting object. This number may be found in the NASA Satellite Situation Report and on the NASA Prediction Bulletins.

Cathode Ray Tube (CRT)

A television picture tube for image display.


Temperature scale proposed by Swedish astronomer Anders Celsius in 1742. A mixture of ice and water is zero on the scale; boiling water is designated as 100 degrees. A degree is defined as one hundredth of the difference between the two reference points, resulting in the term centigrade (100th part).

To convert centigrade to Fahrenheit multiply the centigrade temperature by 1.8 and add 32.

F = 9/5 C + 32

To convert Fahrenheit to centigrade: subtract 32 from the Fahrenheit temperature and divide the quantity by 1.8.

C = (F -32) / 1.8.

Central Processing Unit (CPU)

Main part of a computer consisting of an arithmetic logic unit and a control unit. See microprocessor.

Chlorofluorocarbon (CFC)

A family of compounds of chlorine, fluorine, and carbon, entirely of industrial origin. CFCs include refrigerants, propellants for spray cans {this usage is banned in the U.S., although some other countries permit it) and for blowing plastic-foam insulation, styrofoam packaging, and solvents for cleaning electronic circuit boards. The compounds' lifetimes vary over a wide ranae, exceedinq 100 years in some cases.

CFCs' ability to destroy stratophpeic ozone through catalytic cycles is contributing to the depletion of ozone worldwide. Because CFCs are such stable molecules, they do not react easily with other chemicals in the lower atmosphere. One of the few forces that can break up CFC molecules is ultraviolet radiation, however the ozone layer protects the CFCs from ultraviolet radiation in the lower atmosphere. CFC molecules are then able to migrate intact into the stratosphere, where the molecules are bombarded by ultraviolet rays, causing the CFCs to break up and release their chlorine atoms. The released chlorine atoms participate in ozone destruction, with a single atom of chlorine able to destroy ozone molecules over and over again.

International attention to CFCs resulted in a meeting of diplomats from around the world in Montreal in 1987. They forged a treaty that called for drastic reductions in the production of CFCs. In 1990, diplomats met in London and voted to significantly strengthen the Montreal Protocol by calling for a complete elimination of CFCs by the year 2000. See Montreal Protocal.

Circadian Rhythm

The cyclical changes in physiological processes and functions that are related to the 24-hour diurnal cycle.


The complete path of an electric current; an assemblage of electronic elements; a means of two-way communication between two points - comprised of associated "go" and "return" channels.

Circular Polarized RF

Radio frequency transmissions where the wave energy is divided equally between a vertically and a horizontally-polarized component.

Clarke Belt

A belt 22,245 miles (35,800 kilometers) directly above the equator where a satellite orbits the Earth at the same speed the Earth is rotating. Science fiction writer and scientist Arthur C. Clarke wrote about this belt in 1945, hence the name.


The average weather conditions in an area determined over a period of years.


Science dealing with climate and climate phenomena.


A person or thing very much like another, e.g., a copy of another manufacturer's computer.


Any sudden, heavy rain shower.


A visible mass of water vapor suspended in the atmosphere above Earths surface. Clouds form in areas where air rises and cools. The condensing water vapor forms small droplets of water (0.012 mm) that, when combined with billions of other droplets, form clouds. Clouds can form along warm and cold fronts, where air flows up the side of the mountain and cools as it rises higher into the atmosphere, and when warm air blows over a colder surface, such as a cool body of water.

Clouds fall into two general categories: sheetlike or layer-looking stratus clouds (stratus means layer) and cumulus clouds {cumulus means piled up). These two cloud types are divided into four more groups that describe the clouds altitude

High clouds form above 20,000 feet in the cold region of the troposphere, and are denoted by the prefix CIRRO or CIRRUS. At this altitude water almost always freezes so clouds are composed of ice crystals. The clouds tend to be wispy, are often transparent, and include cirrus, cirrocumulus, and cirrostratus.

Middle clouds form between 6,500 and 20,000 feet and are denoted by the prefix ALTO. They are made of water droplets and include altostratus and altocumulus

Low clouds are found up to 6,500 feet and include the stratocumulus and nimbostratus clouds. When stratus clouds contact the ground they are called fog.

Vertical clouds, such as cumulus, rise far above their bases and can form at many heights. Cumulonimbus clouds, or thunderheads, can start near the ground and soar up to 75.000 feet.

Cloud Streets

Lines or rows of cumuliform clouds.

Coastal Zone Color Scanner (CZCS)

The first spacecraft instrument devoted to measurement of ocean color. Although instruments on other satellites have sensed ocean color, their spectral bands, spatial resolution, and dynamic range were optimized for geographical or meteorological use. In the CZCS, every parameter is optimized for use over water to the exclusion of any other type of sensing. The CZCS flew on the Nimbus-7 spacecraft.

Coaxial Cable

A hollow copper cylinder, or other cylindrical conductor, surrounding a single-wire conductor having a common axis (hence coaxial). The space between the cylindrical shell and the inner conductor is filled with an insulator which may be plastic or mostly air, with supports separating the shell and the inner conductor every inch or so. The cable is used to carry radio frequency signals to or from antennas, etc.

Comma Cloud

Band of organized cumuliform clouds that look like a comma from a satellites perspective. Comma clouds are indicators of heavy storms.

Common Business Oriented Language (COBOL)

A computer programming language written for business application.

Compact Disk-Read Only Memory (CD-ROM)

Type of computer memory that reads and uses information, but does not allow information to be added, changed, or erased. Digital information is read by laser. CD-ROM does not depend upon any proprietary hardware or software, making it an accessible vehicle for electronic publishing.


Electronic machine capable of performing calculations and other manipulations of various types of data, under the control of a stored set of instructions. The machine itself is the hardware; the instructions are the program or software. Depending upon size, computers are called mainframes, minicomputers, and microcomputers. Microcomputers include desk-top and portable personal computers.


Change of a substance to a denser form, such as gas to a liquid. The opposite of evaporation.


The transfer of heat from one substance to another by direct contact. Denser substances are better conductors; the transfer is always from warmer to colder substances.


Condensation trails. Artificial clouds made by the exhaust of jet aircraft.


The rising of warm air and the sinking of cool air. Heat mixes and moves air. When a layer of air receives enough heat from the Earth's surface, it expands and moves upward. Colder, heavier air flows under it which is then warmed, expands, and rises. The warm rising air cools as it reaches higher, cooler regions of the atmosphere and begins to sink. Convection causes local breezes, winds, and thunderstorms.

Coordinated Universal Time (UTC)

(aka Greenwich Mean Time [GMT]) Local time at zero degrees longitude at the Greenwich Observatory, England. UTC uses a 24-hour clock, i.e., 2:00 a.m. is 0200 hours, 2:00 p.m. is 1400 hours, midnight is 2400 or 0000 hundred hours.


One of the large, continuous areas of the Earth into which the land surface is divided. The six geographically defined continents are politically defined as seven:

  1. Africa
  2. Asia
  3. Australia
  4. Europe
  5. North America
  6. South America
  7. Antarctica

Coriolis Force

The apparent tendency of a freely moving particle to swing to one side when its motion is referred to a set of axes that is itself rotating in space, such as Earth. The acceleration is perpendicular to the direction of the speed of the article relative to the Earth's surface and is directed to the right in the northern hemisphere. Winds are affected by rotation of the Earth so that instead of a wind blowing in the direction it starts, it turns to the right of that direction in the northern hemisphere; left in the southern hemisphere.

Coupled System

Two or more processes that affect one another.

Crop Calendar

The schedule of the maturing and harvesting of seasonal crops.


One of the interrelated components of the Earths system, the cryosphere is frozen water in the form of snow, permanently frozen ground (permafrost), floating ice, and glaciers. Fluctuations in the volume of the cryosphere cause changes in ocean sea-level, which directly impact the atmosphere and biosphere.


The point at which a satellite reaches its highest position or elevation in the sky, relative to an observer (aka the closest point of approach).


An area of low pressure where winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. See anticyclone, wind.


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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: May 13 2021

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