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midnight sun
(Encyclopedia)midnight sun, phenomenon in which the sun remains visible in the sky continuously for 24 hr or longer, occurring only in the polar regions. The midnight sun is due to the fact that the plane of the ea...snowball earth
(Encyclopedia)snowball earth, hypothesized condition in which the earth was covered completely by ice during several periods in the Proterozoic. The hypothesis was originally developed to explain evidence of the co...geodesy
(Encyclopedia)geodesy jēŏdˈĭsē [key] or geodetic surveying, theory and practice of determining the position of points on the earth's surface and the dimensions of areas so large that the curvature of the earth...zone
(Encyclopedia)zone [Gr.,=girdle], in geography, area with a certain physical and/or cultural unity that distinguishes it from other areas. The division of the earth into five climatic zones probably originated (5th...Roe v. Wade
(Encyclopedia)Roe v. Wade, case decided in 1973 by the U.S. Supreme Court. Along with Doe v. Bolton, this decision legalized abortion in the first trimester of ...frost
(Encyclopedia)frost or hoarfrost, ice formed by the condensation of atmospheric water vapor on a surface when the temperature of the surface is below 32℉ (0℃). In the formation of frost, a gas (water vapor) is ...Paleocene epoch
(Encyclopedia)Paleocene epoch pāˈlēəsēnˌ [key], first epoch of the Tertiary period in the Cenozoic era of geologic time (see geologic timescale) between 60 to 66 million years ago. In W North America, the upl...wind
(Encyclopedia)wind, flow of air relative to the earth's surface. A wind is named according to the point of the compass from which it blows, e.g., a wind blowing from the north is a north wind. The diurnal, or dai...daylight saving time
(Encyclopedia)daylight saving time (DST), time observed when clocks and other timepieces are set ahead so that the sun will rise and set later in the day as measured by civil time. The amount of daylight on a given...seasons
(Encyclopedia)CE5 The seasons are caused by the tilt of the earth's axis to the plane of its orbit about the sun. The Northern Hemisphere is tilted toward the sun in the summer and receives more direct rays than...Browse by Subject
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