![Radio telescope system.[Credits : Encyclopædia Britannica, Inc.]](http://media-2.web.britannica.com/eb-media/34/4634-003-7EA37D44.gif)
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.
![Lovell Telescope, a fully steerable radio telescope at Jodrell Bank, Macclesfield, Cheshire, Eng.[Credits : Jodrell Bank Science Centre]](http://media-2.web.britannica.com/eb-media/90/3690-003-3BF38FFC.gif)
The first radio telescope, built in 1937 by Grote Reber 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, Cheshire, Eng., has a steerable paraboloid antenna 76 m (250 feet) in diameter. The reflecting surface of the telescope at Arecibo, 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.
Radio interferometers 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 | |||||
| name | diameter of dish (metres) | short wavelength limit (cm) | location | ||
| Filled-aperture telescopes | |||||
| Arecibo Observatory | 305 | 6 | Arecibo, P.R. | ||
| Green Bank Telescope | 110 x 100 | 0.3 | Green Bank, W.Va., U.S. | ||
| Effelsberg Radio Telescope | 100 | 1 | Effelsberg, Ger. | ||
| Lovell Telescope | 76 | 6 | Jodrell Bank, Cheshire, Eng. | ||
| Parkes Observatory | 64 | 1 | Parkes, N.S.W., Austl. | ||
| IRAM Pico Veleta Observatory | 30 | 0.1 | Pico Veleta, Spain | ||
| Haystack Radio Telescope | 37 | 0.3 | Westford, Mass., U.S. | ||
| RATAN-600 | 576 | 1 | Zelenchukskaya, Russia | ||
| Nobeyama Radio Observatory 45-m Telescope | 45 | 0.1 | Nobeyama, Japan | ||
| Caltech Submillimeter Observatory | 10 | 0.05 | Mauna Kea, Hawaii, U.S. | ||
| James Clerk Maxwell Telescope | 15 | 0.04 | Mauna Kea, Hawaii, U.S. | ||
| Heinrich Hertz Submillimeter Telescope | 10 | 0.06 | Mount Graham, Ariz., U.S. | ||
| name | size of array (km) | number of dishes | diameter of dish (metres) | short wavelength limit (cm) | location |
| Arrays | |||||
| Very Large Array | 36 | 27 | 25 | 0.7 | Socorro, N.M., U.S. |
| Westerbork Synthesis Radio Telescope | 3.2 | 14 | 25 | 6 | Westerbork, Neth. |
| Australia Telescope Compact Array | 3 | 6 | 22 | 0.3 | Narrabari, N.S.W., Austl. |
| Very Long Baseline Array | 8,000 | 10 | 25 | 0.3 | U.S. Virgin Islands to Hawaii |
| Combined Array for Research in Millimeter-wave Astronomy | 2 | 16 | 6 x 10 m, 10 x 6 m | 0.1 | Big Pine, Calif., U.S. |
| Submillimeter Array | 0.5 | 8 | 6 | 0.03 | Mauna Kea, Hawaii, U.S. |
| Giant Metrewave Wavelength Telescope | 25 | 30 | 45 | 21 | Pune, India |
| Multi-Element Radio Linked Interferometer Network | 217 | 7 | 1 x 76 m, 1 x 32 m, 1 x (32 x 25) m, 4 x 25 m | 1.3 | southern England |
| IRAM Plateau de Bure Interferometer | 0.4 | 6 | 15 | 0.1 | Plateau de Bure, France |
| Nobeyama Millimeter Array | 0.6 | 6* | 10 | 0.1 | Nobeyama, Japan |
| *Sometimes the Nobeyama 45-metre filled-aperture telescope is used as a seventh dish of this array. | |||||
Radio-telescope-systemRadio telescope system.[Credits : Encyclopædia Britannica, Inc.]
Lovell-Telescope-a-fully-steerable-radio-telescope-at-Jodrell-BankLovell Telescope, a fully steerable radio telescope at Jodrell Bank, Macclesfield, Cheshire, Eng.[Credits : Jodrell Bank Science Centre]
VLA-image-of-an-interacting-twin-jet-radio-galaxyVLA (Very Large Array) image of an interacting twin-jet radio galaxy. The two black dots (at the …[Credits : Courtesy of the National Radio Astronomy Observatory/Associated Universities, Inc.]
The-Very-Large-Array-near-Socorro-NMThe Very Large Array near Socorro, N.M.[Credits : NRAO—AUI/Dave Finley]
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