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light-year
light-year in astronomy, unit of length equal to the distance light travels in one sidereal year . It is 9.461 × 10 12 km (about 6 million million mi). Alpha Centauri and Proxima Centauri, the stars nearest our solar system, are about 4.3 light-years distant. See also parsec .
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Malayo-Polynesian languages
Malayo-Polynesian languages , sometimes also called Austronesian languages , family of languages estimated at from 300 to 500 tongues and understood by approximately 300 million people in Madagascar; the Malay Peninsula; Indonesia and New Guinea; the Philippines; Taiwan; the Melanesian, Micronesi...
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dating, radioactive
dating, radioactive (radiometric dating) Any of several methods using radioactive decay to assess the ages of archaeological remains, fossils and rocks. The specimens must contain a very long-lived radioisotope of known half-life (time taken for one half of its nuclei to decay), which, with a measu...
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refugee
refugee one who leaves one's native land either because of expulsion or to escape persecution. The legal problem of accepting refugees is discussed under asylum ; this article considers only mass dislocations and the organizations that help refugees.
The Rise of International Refugee Organiz...
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Bantu languages
Bantu languages group of African languages forming a subdivision of the Benue-Niger division of the Niger-Congo branch of the Niger-Kordofanian language family (see African languages ). Bantu contains hundreds of languages that are spoken by 120 million Africans in the Congo Basin, Angola, the Rep...
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wilderness
wilderness land retaining its primeval character with the imprint of humans minimal or unnoticeable. In the United States, the Wilderness Act of 1964 established the National Wilderness Preservation System with a nucleus of 9 million acres (3.6 million hectares) of land in 54 different areas, mostl...
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Cenozoic era
Cenozoic era , last major division of geologic time (see Geologic Timescale , table) lasting from 65 million years ago to the present. The Cenozoic is divided into the Tertiary (from 65 million years ago until 2 million years ago) and Quaternary (2 million years ago to the present) periods. Early i...
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airline industry
airline industry the business of transporting paying passengers and freight by air along regularly scheduled routes, typically by airplanes but also by helicopter.
Ferdinand Graf von Zeppelin set up the first commercial airline in 1912, using a form of the dirigible to transport more than 34...
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migration
migration of people, geographical movements of individuals or groups for the purpose of permanently resettling.
Early History
Migrations have occurred throughout history and have played an important part in the peopling of all the areas of the earth. Primitive migrations were usually in s...
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Earth
Earth The third planet in the solar system, outwards from the Sun. The mean distance of the Earth from the Sun is 149.6 × 106 km. This distance provides the standard ‘astronomical unit’ (AU) of measurement. The Earth has a mean radius of 6371 km, density of 5517 kg/m3, and a mass ...
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