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heath, tract of open land
(Encyclopedia)heath, tract of open land characterized by a few scattered trees, abundant moss cover, and numerous low shrubs, principally of the heath family (see heath, in botany). In high-latitude regions with mi...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 ...Picard, Jean
(Encyclopedia)Picard, Jean, 1620–82, French astronomer, noted for having made the first accurate measurement of a degree of the earth's meridian. The figures he established were of great value to Newton in his ca...snow line
(Encyclopedia)snow line, altitude above which or latitude beyond which snow does not melt in summer (usually called the permanent snow line), or, in winter, the line to which snow extends at a given point in time. ...galactic coordinate system
(Encyclopedia)galactic coordinate system, astronomical coordinate system in which the principal axis is the galactic equator (the intersection of the plane of the Milky Way with the celestial sphere) and the refere...timberline
(Encyclopedia)timberline, elevation above which trees cannot grow. Its location is influenced by the various factors that determine temperature, including latitude, prevailing wind directions, and exposure to sunli...Tropic of Cancer
(Encyclopedia)Tropic of Cancer, parallel of latitude at 23°30′ north of the equator; it is the northern boundary of the tropics. This parallel marks the farthest point north at which the sun can be seen directly...Tropic of Capricorn
(Encyclopedia)Tropic of Capricorn, parallel of latitude at 23°30′ south of the equator; it is the southern boundary of the tropics. This parallel marks the farthest point south at which the sun can be seen direc...celestial pole
(Encyclopedia)celestial pole, one of the two points at which the earth's axis of rotation intersects the celestial sphere. The celestial pole is important as a reference point in the equatorial coordinate system; t...navigation
(Encyclopedia)navigation, science and technology of finding the position and directing the course of vessels and aircraft. The next great revolution in navigation occurred in the 20th cent., when radio signals ...Browse by Subject
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