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perturbation

(Encyclopedia)perturbation pŭrˌtərbāˈshən [key], in astronomy and physics, small force or other influence that modifies the otherwise simple motion of some object. The term is also used for the effect produce...

Egyptian architecture

(Encyclopedia)Egyptian architecture, the architecture of the ancient Egyptians, formulated prior to 3000 b.c. and lasting through the Ptolemaic period (323–30 b.c.). Egyptian architectural development parallel...

Galileo

(Encyclopedia)Galileo (Galileo Galilei) gălˌĭlēˈō; gälēlĕˈō gälēlĕˈē [key], 1564–1642, great Italian astronomer, mathematician, and physicist. By his persistent investigation of natural laws he la...

universe

(Encyclopedia)universe, totality of matter and energy in existence. The study of the origin of the universe, or cosmos, is known as cosmogony, and that of its structure and evolution, cosmology. The age of the univ...

migration of animals

(Encyclopedia)migration of animals, movements of animals in large numbers from one place to another. In modern usage the term is usually restricted to regular, periodic movements of populations away from and back t...

Field, Marshall

(Encyclopedia)Field, Marshall, 1834–1906, American merchant, b. Conway, Mass. In 1856, after five years' apprenticeship in a general store in Pittsfield, Mass., he went to Chicago and became a clerk for Cooley, W...

Grand Canyon

(Encyclopedia)Grand Canyon, great gorge of the Colorado River, one of the natural wonders of the world; c.1 mi (1.6 km) deep, from 4 to 18 mi (6.4–29 km) wide, and 217 mi (349 km) long, NW Ariz. The canyon shows ...

neutrino astronomy

(Encyclopedia)neutrino astronomy, study of stars by means of their emission of neutrinos, fundamental particles that result from nuclear reactions and are emitted by stars along with light. Approximately 100 billio...

Pachacamac

(Encyclopedia)Pachacamac päˌchäkämäkˈ [key], ruins of a walled Native American settlement, Peru, about 25 mi (40 km) SE of Lima in the Lurin Valley. This site, which contains a number of pyramids, was conside...

Pawnee

(Encyclopedia)Pawnee pônēˈ [key], Native North Americans whose language belongs to the Caddoan branch of the Hokan-Siouan linguistic stock (see Native American languages). At one time the Pawnee lived in what is...