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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...

earth, in geology and astronomy

(Encyclopedia)CE5 A. Cross section of the earth, showing its shells B. Detailed cross section of the crust and upper mantle: The lithosphere consists of the hard rock in the crust and upper mantle, lying above t...

Arctic, the

(Encyclopedia)CE5 Arctic, the northernmost area of the earth, centered on the North Pole. The arctic regions are not coextensive with the area enclosed by the Arctic Circle (lat. 66°30′N) but are usually defi...

Maya, indigenous people of Mexico and Central America

(Encyclopedia)Maya mīˈə, Span. mäˈyä [key], indigenous people of S Mexico and Central America, occupying an area comprising the Yucatán peninsula and much of the present state of Chiapas in Mexico, Guatemala...

Hapsburg

(Encyclopedia)Hapsburg or Habsburg both: hăpsˈbûrg, Ger. häpsˈbo͝ork [key], ruling house of Austria (1282–1918). In the 19th cent. the Hapsburg position was challenged in Germany by Prussia, in Italy b...

Washington, D.C.

(Encyclopedia)Washington, D.C., capital of the United States, coextensive (since 1878, when Georgetown became a part of Washington) with the District of ...

nucleus, in physics

(Encyclopedia)nucleus, in physics, the extremely dense central core of an atom. Following the discovery of radioactivity by A. H. Becquerel in 1896, Ernest Rutherford identified two types of radiation given off b...

Delaware, state, United States

(Encyclopedia)CE5 Delaware dĕlˈəwâr, –wər [key], one of the Middle Atlantic states of the United States, the country's second smallest state (after Rhode Island). It is bordered by Maryland (W, S), and th...

Maryland

(Encyclopedia)CE5 Maryland mârˈələnd [key], one of the Middle Atlantic states of the United States. It is bounded by Delaware and the Atlantic Ocean (E), the District of Columbia (S), Virginia and West Virgi...

Mauritania

(Encyclopedia)CE5 Mauritania môrĭtāˈnēə [key], officially Islamic Republic of Mauritania, republic (2015 est. pop. 4,182,000), 397,953 sq mi (1,030,700 sq km), NW Africa. It borders on the Atlantic Ocean i...