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celestial mechanics

(Encyclopedia)celestial mechanics, the study of the motions of astronomical bodies as they move under the influence of their mutual gravitation. Celestial mechanics analyzes the orbital motions of planets, dwarf pl...

calendar

(Encyclopedia)calendar [Lat., from Kalends], system of reckoning time for the practical purpose of recording past events and calculating dates for future plans. The calendar is based on noting ordinary and easily o...

liturgy, Islamic

(Encyclopedia)liturgy, Islamic, mandatory ritual prayer in Islam (salat) is performed five times a day at dawn, noon, afternoon, sunset, and night. It requires ritual cleanliness, and is preceded by ablutions. The ...

Three Kingdoms

(Encyclopedia)Three Kingdoms, period of Chinese history from 220 to 265, after the collapse of the Han dynasty. The period takes its name from the three states into which China was divided. Wei occupied the north. ...

Wollaston, William Hyde

(Encyclopedia)Wollaston, William Hyde, 1766–1828, English scientist, M.D. Cambridge, 1793. His wide-ranging scientific achievements include the discovery (1802) of the dark lines (Fraunhofer lines) in the solar s...

Brahic, André Fernand

(Encyclopedia)Brahic, André Fernand, 1942–2016, French astrophysicist, b. Paris. He was introduced to astrophysics by Evry Schatzman, a leading French theoretician, and obtained his doctorate from the Univ. of P...

ultraviolet astronomy

(Encyclopedia)ultraviolet astronomy, study of celestial objects by means of the ultraviolet radiation they emit, in the wavelength range from about 90 to about 350 nanometers. Ultraviolet (UV) line spectrum measure...

water, desalination of

(Encyclopedia)water, desalination of, process of removing soluble salts from water to render it suitable for drinking, irrigation, or industrial uses. The principal methods used for desalination include distillatio...

light-year

(Encyclopedia)light-year, in astronomy, unit of length equal to the distance light travels in one sidereal year. It is 9.461 × 1012 km (about 6 million million mi). Alpha Centauri and Proxima Centauri, the stars n...

doldrums

(Encyclopedia)doldrums dŏlˈdrəmz [key] or equatorial belt of calms, area around the earth centered slightly north of the equator between the two belts of trade winds. The large amount of solar radiation that arr...