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Ulugh-Beg

(Encyclopedia)Ulugh-Beg or Ulug-Beg both: o͞oˈlo͞og bĕg [key], 1394–1449, Timurid ruler and astronomer. The grandson of Timur (or Tamerlane), he succeeded to the Timurid domain in 1447. A patron of the arts a...

electromagnetic radiation

(Encyclopedia)CE5 Electromagnetic spectrum electromagnetic radiation, energy radiated in the form of a wave as a result of the motion of electric charges. A moving charge gives rise to a magnetic field, and if ...

European Space Agency

(Encyclopedia)European Space Agency (ESA), multinational agency dedicated to the promotion, for exclusively peaceful purposes, of cooperation among European states in space research and technology. Member states in...

Al-Farghani

(Encyclopedia)Al-Farghani ălfrəgāˈnəs [key], d. after 861, Arab astronomer. Al-Farghani was born in Farghana, Transoxania (present-day Fergana, Uzbekistan), and died in Egypt. His most important work, written ...

hour circle

(Encyclopedia)hour circle, in astronomy, a secondary axis in the equatorial coordinate system. The hour circle of a celestial body is the great circle on the celestial sphere that passes through both the body and t...

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...

Maclaurin, Colin

(Encyclopedia)Maclaurin, Colin məklôrˈĭn, –lärˈĭn [key], 1698–1746, Scottish mathematician and natural philosopher, one of the greatest mathematicians of his time. He was professor at Aberdeen and from 1...

Rømer, Olaus

(Encyclopedia)Rømer, Olaus or Ole ōläˈo͝os, ōˈlə römˈər [key], 1644–1710, Danish astronomer. He is noted for his discovery that light travels at a definite speed and does not move through space instant...

Brahmagupta

(Encyclopedia)Brahmagupta bräˌməgo͝opˈtə [key], c.598–c.660, Indian mathematician and astronomer. He was among the first to meaningfully discuss the concepts of zero and of negative numbers. He wrote in ver...

Blaeu, Willem Janszoon

(Encyclopedia)Blaeu, Willem Janszoon vĭˈləm yänˈsōn blou [key], 1571–1638, Dutch cartographer and printer. He studied astronomy and instrument making under the Danish astronomer Tycho Brahe. The printing es...