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altitude

(Encyclopedia)altitude, vertical distance of an object above some datum plane, such as mean sea level or a reference point on the earth's surface. It is usually measured by the reduction in atmospheric pressure wit...

synchrotron radiation

(Encyclopedia)synchrotron radiation, in physics, electromagnetic radiation emitted by high-speed electrons spiraling along the lines of force of a magnetic field (see magnetism). Depending on the electron's energy ...

chlorophyll

(Encyclopedia)CE5 chlorophyll klôrˈəfĭlˌ [key], green pigment that gives most plants their color and enables them to carry on the process of photosynthesis. Chemically, chlorophyll has several similar forms...

thallium

(Encyclopedia)thallium thălˈēəm [key], metallic chemical element; symbol Tl; at. no. 81; interval in which at. wt. ranges 204.382–204.385; m.p. 303.5℃; b.p. about 1,457℃; sp. gr. 11.85 at 20℃; valence +...

Lewis, Sir George Cornewall

(Encyclopedia)Lewis, Sir George Cornewall, 1806–63, English statesman and man of letters. Entering Parliament as a Liberal in 1847, he served as chancellor of exchequer (1855–58), home secretary (1859–61), an...

Amici, Giovanni Battista

(Encyclopedia)Amici, Giovanni Battista jōvänˈnē bät-tēsˈtä ämēˈchē [key], 1786–1863, Italian astronomer, mathematician, and naturalist. He became director of the observatory and professor of astronomy...

Apianus, Petrus

(Encyclopedia)Apianus, Petrus pāˈtər bēˈnəvĭts, bĕnˈəvĭts [key], 1495–1552, German cosmographer and mathematician. He was professor of mathematics at Ingolstadt and was noted for his knowledge of astro...

quadrature

(Encyclopedia)quadrature, in astronomy, arrangement of two celestial bodies at right angles to each other as viewed from a reference point. If the reference point is the earth and the sun is one of the bodies, a pl...

Abbo of Fleury

(Encyclopedia)Abbo of Fleury äbōˈ, flörēˈ [key], Fr. Abbon de Fleury, 945?–1004, French monk at the abbey of Fleury (at present-day Saint-Benoît-sur-Loire, France). Head of the monastery school, he later t...

blink microscope

(Encyclopedia)blink microscope, in astronomy, device for determining a change in position or magnitude (brightness) of a star relative to other stars in the background. Two photographs of the same field or area of ...