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Definition of TELESCOPE
: a usually tubular optical instrument for viewing distant objects by means of the refraction of light rays through a lens or the reflection of light rays by a concave mirror — compare reflector, refractor
: any of various tubular magnifying optical instruments
Device that collects light from and magnifies images of distant objects, undoubtedly the most important investigative tool in astronomy. The first telescopes focused visible light by refraction through lenses; later instruments used reflection from curved mirrors (seeoptics). Their invention is traditionally credited to Hans Lippershey (1570?–1619?), who adapted A. van Leeuwenhoek's use of lenses in microscopes. Among the earliest telescopes were Galilean telescopes, modeled after the simple instruments built by Galileo, who was the first to use telescopes to study celestial bodies. In 1611 Johannes Kepler proposed an improved version that became the basis for modern refracting instruments. The reflecting telescope came into its own after William Herschel (seeHerschel family) used one to discover the planet Uranus in 1781. Since the 1930s radio telescopes have been used to detect and form images from radio waves emitted by celestial objects. More recently, telescopes have been designed to observe objects and phenomena in other parts of the electromagnetic spectrum (seegamma-ray astronomy; infrared astronomy; ultraviolet astronomy; X-ray astronomy). Spaceflight has allowed telescopes to be launched into Earth orbit to avoid the light-scattering and light-absorbing effects of the atmosphere (e.g., the Hubble Space Telescope). See alsobinoculars; observatory.