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Theodosius II
(Encyclopedia)Theodosius II, 401–50, Roman emperor of the East (408–50), son and successor of Arcadius. He preferred the study of theology and astronomy to public affairs, which he left to the guidance of his s...radar
(Encyclopedia)radar, system or technique for detecting the position, movement, and nature of a remote object by means of radio waves reflected from its surface. Although most radar units use microwave frequencies, ...solstice
(Encyclopedia)solstice sŏlˈstĭs [key] [Lat.,=sun stands still], in astronomy, either of the two points on the ecliptic that lie midway between the equinoxes (separated from them by an angular distance of 90°). ...Copernican system
(Encyclopedia)Copernican system, first modern European theory of planetary motion that was heliocentric, i.e., that placed the sun motionless at the center of the solar system with all the planets, including the ea...Sagan, Carl Edward
(Encyclopedia)Sagan, Carl Edward sāˈgən [key], 1934–96, American astronomer and popularizer of science, b. New York City. Early in his career he investigated radio emissions from Venus and concluded that the c...Struve
(Encyclopedia)Struve shtro͞oˈvə [key], family of astronomers. Friedrich Georg Wilhelm von Struve, 1793–1864, was born in Germany but later lived in Russia. While director (1817–39) of Dorpat Observatory he w...revolution
(Encyclopedia)revolution, in a political sense, fundamental and violent change in the values, political institutions, social structure, leadership, and policies of a society. The totality of change implicit in this...Barnard, Frederick Augustus Porter
(Encyclopedia)Barnard, Frederick Augustus Porter, 1809–89, American educator and mathematician, b. Sheffield, Mass., grad. Yale, 1828. After tutoring at Yale and teaching in institutions for the deaf and mute, he...zero
(Encyclopedia)zero, that number which, when added to any number, leaves the latter unchanged; its symbol is 0. The introduction of zero into the decimal system was the most significant achievement in the developmen...gamma radiation
(Encyclopedia)gamma radiation, high-energy photons emitted as one of the three types of radiation resulting from natural radioactivity. It is the most energetic form of electromagnetic radiation, with a very short ...Browse by Subject
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