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glacial periods
(Encyclopedia)glacial periods, times during which large portions of the earth's surface were covered with thick glacial ice sheets. In the Pleistocene epoch, in the Carboniferous and Permian periods of the Paleozoi...Energy, United States Department of
(Encyclopedia)Energy, United States Department of, executive department of the federal government responsible for coordinating national activities relating to the production, regulation, marketing, and conservation...corona, in astronomy
(Encyclopedia)corona, luminous envelope surrounding the sun, outside the chromosphere. Its density is less than one billionth that of the earth's atmosphere. The corona is visible only at the time of totality durin...sidereal year
(Encyclopedia)sidereal year, time required for the earth to complete an orbit of the sun relative to the stars. The sidereal year is 365 days, 6 hr, 9 min, 9.5 sec of mean solar time (see solar time). It is 20 min ...Young, Charles Augustus
(Encyclopedia)Young, Charles Augustus, 1834–1908, American astronomer, b. Hanover, N.H., grad. Dartmouth, 1853. He discovered the reversing layer of the solar atmosphere and proved the gaseous nature of the sun's...pulsar
(Encyclopedia)pulsar, in astronomy, a neutron star that emits brief, sharp pulses of energy instead of the steady radiation associated with other natural sources. The study of pulsars began when Antony Hewish and h...Atacama Desert
(Encyclopedia)Atacama Desert ätäkäˈmä [key], arid region, c.600 mi (970 km) long, N Chile, extending south from the border of Peru. The desert itself, c.2,000 ft (610 m) above sea level, is a series of dry sal...cycle
(Encyclopedia)cycle, in astronomy, period of time required for the recurrence of some celestial event. The length of a cycle may be measured relative to the sun or to the fixed stars (see sidereal time). A frequent...nebular hypothesis
(Encyclopedia)nebular hypothesis: see solar system. ...protoplanet theory
(Encyclopedia)protoplanet theory: see solar system. ...Browse by Subject
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