radio telescope

radio telescope
a system consisting of an antenna, either parabolic or dipolar, used to gather radio waves emitted by celestial sources and bring them to a receiver placed in the focus.
[1925-30]

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Combination of radio receiver and antenna, used for observation in radio and radar astronomy.

Radio telescopes vary widely, but all have two basic components: a large radio antenna or an antenna array and a radiometer or radio receiver. Because some astronomical radio sources are extremely weak, radio telescopes are usually very large, and only the most sensitive radio receivers are used. The first large fully steerable radio telescope was completed in 1957 at Jodrell Bank, Eng. The world's largest fully steerable radio telescope is the 360 × 330-ft (110 × 100-m) off-axis antenna operated by the National Radio Astronomy Observatory in Green Bank, W.Va. The largest single radio telescope is the 1,000-ft (305-m) fixed spherical reflector at the Arecibo Observatory in Puerto Rico. The world's most powerful radio telescope is the Very Large Array in New Mexico, made up of 27 separate mobile parabolic antennas that together provide the angular resolution of a single antenna 22 mi (35 km) in diameter.

Lovell Telescope, a fully steerable radio telescope at Jodrell Bank, Macclesfield, Cheshire, Eng.

Jodrell Bank Science Centre

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▪ astronomical instrument
 astronomical instrument consisting of a radio receiver and an antenna system that is used to detect radio-frequency radiation emitted by extraterrestrial sources. Because radio wavelengths are much longer than those of visible light, radio telescopes must be very large in order to attain the resolution of optical telescopes.

      A brief treatment of radio telescopes follows. For full treatment, see telescope.

 The first radio telescope, built in 1937 by Grote Reber (Reber, Grote) of Wheaton, Ill., U.S., was a steerable paraboloid—i.e., a device with a parabolically shaped reflector, dubbed the “dish,” that focuses the incoming radio waves onto a small pickup antenna, or “feed.” The radio telescope at Jodrell Bank (Jodrell Bank Observatory), Cheshire, Eng., has a steerable paraboloid antenna 76 m (250 feet) in diameter. The reflecting surface of the telescope at Arecibo (Arecibo Observatory), P.R., fills a naturally occurring bowl-shaped depression 305 m (1,000 feet) in diameter. The Arecibo installation is equipped with a radar transmitter for the study of radar signals reflected from such celestial objects as planets and their satellites.

       Some important radio telescopesRadio interferometers (radio interferometer) consist of two or more widely separated antennas connected by transmission lines. With their greatly increased resolving power, they can be used to determine the position or diameter of a radio source or to separate two closely spaced sources. Phase-array telescopes consist of large numbers of relatively small antenna elements arranged in any of various configurations over a relatively large area, yielding the effective sensitivity and resolution of an antenna much larger than could practicably be built. An example of such a system is the 27-antenna Very Large Array near Socorro, N.M., which is one of the world's largest and most sensitive radio telescopes. See also telescope. Some important radio telescopes

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