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lighthouse
(Encyclopedia)lighthouse, towerlike structure erected to give guidance and warning to ships and aircraft by either visible or radioelectrical means. Lighthouses were long built to conform in structure to their geog...green flash
(Encyclopedia)green flash or emerald flash, a refractive phenomenon of the atmosphere where the top edge of the setting (or, less frequently, rising) sun will momentarily turn emerald green. The green color lasts f...sky
(Encyclopedia)sky, apparent dome over the earth, background of the clouds, sun, moon, and stars. The blue color of the clear daytime sky results from the selective scattering of light rays by the minute particles o...ophthalmoscope
(Encyclopedia)ophthalmoscope ŏfthălˈməskōpˌ [key], instrument used for examining the inner structure of the eye. The device was invented by the German physiologist H. L. F. von Helmholtz in 1851. His model co...Orion Nebula
(Encyclopedia)Orion Nebula, bright diffuse nebula in the constellation Orion; also known as the Great Nebula of Orion and cataloged as M42 or NGC 1976. It is located near the middle of the “sword” hanging from ...prism
(Encyclopedia)prism, in optics, a piece of translucent glass or crystal used to form a spectrum of light separated according to colors. Its cross section is usually triangular. The light becomes separated because d...seasonal affective disorder
(Encyclopedia)seasonal affective disorder (SAD), recurrent fall or winter depression characterized by excessive sleeping, social withdrawal, depression, overeating, and pronounced weight gain. SAD effects an estima...aberration
(Encyclopedia) CE5 A. Spherical aberration: Light rays near the edge of the lens are bent more and brought to focus nearer to the lens. B. Chromatic aberration: Shorter wavelengths (higher frequencies) are bent m...chiaroscuro
(Encyclopedia)chiaroscuro kyärōsko͞oˈrō [key] [Ital.,=light and dark], term once applied to an early method of printing woodcuts from several blocks and also to works in black and white or monotone. Today it i...Finsen, Niels Ryberg
(Encyclopedia)Finsen, Niels Ryberg nēls rüˈbĕr fĭnˈsən [key], 1860–1904, Danish physician. He established in Copenhagen an institute of light therapy and wrote several books on his work. He received the 19...Browse by Subject
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