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focus

(Encyclopedia)focus, in optics, the point at which rays converge after reflection by a concave mirror or refraction by a convex lens, also known as a real focus. The point from which rays appear to diverge after re...

Antarctic Circle

(Encyclopedia)Antarctic Circle, imaginary circle on the surface of the earth at 661⁄2°S lat., i.e., 231⁄2° north of the South Pole. It marks the southernmost point at which the sun can be seen at the winter s...

Arctic Circle

(Encyclopedia)Arctic Circle, imaginary circle on the surface of the earth at 661⁄2°N latitude, i.e., 231⁄2° south of the North Pole. It marks the northernmost point at which the sun can be seen at the winter ...

Pelotas

(Encyclopedia)Pelotas pəlôˈtəsh [key], city (1991 pop. 291,100), Rio Grande do Sul state, S Brazil, an inland port on the São Gonçalo canal. It is a major export point for the stock-raising region of S Rio Gr...

Campina Grande

(Encyclopedia)Campina Grande kəmpēˈnä gränˈdĭ [key], city, Paraíba state, NE Brazil, on the...

lubrication

(Encyclopedia)lubrication, introduction of a substance between the contact surfaces of moving parts to reduce friction and to dissipate heat. A lubricant may be oil, grease, graphite, or any substance—gas, liquid...

circle

(Encyclopedia)CE5 Circle circle, closed plane curve consisting of all points at a given distance from some fixed point, called the center. A circle is a conic section cut by a plane perpendicular to the axis of...

United States Military Academy

(Encyclopedia)United States Military Academy, at West Point, N.Y.; for training young men and women to be officers in the U.S. army; founded and opened in 1802. The original act provided that the Corps of Engineers...

antifreeze

(Encyclopedia)antifreeze, substance added to a solvent to lower its freezing point. The solution formed is called an antifreeze mixture. Antifreeze is typically added to water in the cooling system of an internal-c...

altazimuth coordinate system

(Encyclopedia)altazimuth coordinate system ăltăzˈəməth [key] or horizon coordinate system, astronomical coordinate system in which the position of a body on the celestial sphere is described relative to an obs...