Columbia Encyclopedia

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observatory

(Encyclopedia)observatory, scientific facility especially equipped to detect and record naturally occurring scientific phenomena. Although geological and meteorological observatories exist, the term is generally ap...

credit card

(Encyclopedia)credit card, device used to obtain consumer credit at the time of purchasing an article or service. Credit cards may be issued by a business, such as a department store or an oil company, to make it e...

sunspots

(Encyclopedia)sunspots, dark, usually irregularly shaped spots on the sun's surface that are actually solar magnetic storms. The spots are darker because the temperature of the spots is lower than that of the surro...

quantum theory

(Encyclopedia)quantum theory, modern physical theory concerned with the emission and absorption of energy by matter and with the motion of material particles; the quantum theory and the theory of relativity togethe...

tide

(Encyclopedia)tide, alternate and regular rise and fall of sea level in oceans and other large bodies of water. These changes are caused by the gravitational attraction of the moon and, to a lesser extent, of the s...

information theory

(Encyclopedia)information theory or communication theory, mathematical theory formulated principally by the American scientist Claude E. Shannon to explain aspects and problems of information and communication. Whi...

Mound Builders

(Encyclopedia)Mound Builders, in North American archaeology, name given to those people who built mounds in a large area from the Great Lakes to the Gulf of Mexico and from the Mississippi River to the Appalachian ...

broadcasting

(Encyclopedia)broadcasting, transmission, usually using radio frequencies, of sound or images to a large number of radio or television receivers. In the United States the first regularly scheduled radio broadcasts ...

birth

(Encyclopedia)birth or labor, delivery of the fetus by the viviparous mammal. Birth is also known as parturition. Human birth normally occurs about 280 days after onset of the last menstrual period before conceptio...

air navigation

(Encyclopedia)air navigation, science and technology of determining the position of an aircraft with respect to the surface of the earth and accurately maintaining a desired course (see navigation). Basic to air ...