Radio telescope

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The 64 metre radio telescope at Parkes Observatory, New South Wales, Australia
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The 64 metre radio telescope at Parkes Observatory, New South Wales, Australia

In contrast to an "ordinary" telescope, which produces visible light images, a radio telescope "sees" radio waves emitted by radio sources, typically by means of a large parabolic ("dish") antenna, or arrays of them. The first of these was the 9m telescope constructed by Grote Reber in 1937. In the early 1950s the Cambridge Interferometer mapped the radio sky to produce the famous 2C and 3C surveys of radio sources. In the late 1950s and early 1960s the largest single-dish radio telescope in the world was the 76 metre telescope at Jodrell Bank, which became operational in 1957. This was just the latest of many radio telescopes constructed during the middle of the 20th Century, and has been surpassed by more modern telescopes and arrays of telescopes.

The Very Large Array. As with many radio telescopes, this is an interferometric array formed from many smaller telescopes.
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The Very Large Array. As with many radio telescopes, this is an interferometric array formed from many smaller telescopes.

The largest individual radio telescope is the RATAN-600 (Russia) with 576 meter diameter of circular antenna (RATAN-600 description). The largest radio telescope in Europe is the 100 meter diameter antenna in Effelsberg, Germany, which also was the largest fully steerable telecope for 30 years until the Green Bank Telescope was opened in 2000. The largest radio telescope in the United States until 1998 was Ohio State University's The Big Ear. A typical size of the single antenna of a radio telescope is 25 metre, dozens of radio telescopes with comparable sizes are operated in radio observatories all over the world.

The best-known (although only steerable within about 20° of the zenith) radio telescope probably is the Arecibo radio telescope located in Arecibo, Puerto Rico.

Another well-known radio telescope is the Very Large Array (VLA), in Socorro, New Mexico. This telescope consists of an interferometric array formed from several receivers. The largest exisiting radio telescope array is the Giant Metrewave Radio Telescope, located in Pune, India. A larger array, LOFAR (the 'LOw Frequency ARray') is currently being constructed in western Europe, consisting of 25000 small antennas over an area of several 100s of kilometres in diameter.

The sub-field of astronomy related to observations made through radio telescopes is known as radio astronomy.

Another common design of radio telescope is called a cylindrical paraboloid telescope (actually the receiver shape is a parabolic prism, in this case constructed from wire mesh)
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Another common design of radio telescope is called a cylindrical paraboloid telescope (actually the receiver shape is a parabolic prism, in this case constructed from wire mesh)

Many celestial objects, such as pulsars or active galaxies (like quasars), produce radio-frequency radiation and so are best "visible" or even only visible in the radio region of electromagnetic spectrum. By examining the frequency, power and timing of radio emissions from these objects, astronomers can improve our understanding of the Universe.

Radio telescopes are also occasionally involved in SETI and tracking space probes (see Deep Space Network).

Beginnings

Grote Reber (December 22, 1911 – December 20, 2002) was one of the pioneers of radio astronomy. He was instrumental in repeating Karl Guthe Jansky's pioneering but somewhat simple work, and conducted the first sky survey in the radio frequencies.

See also

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