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Radio telescope

2007 Schools Wikipedia Selection. Related subjects: Engineering; Space
(Astronomy)

   The 64 metre radio telescope at Parkes Observatory
   Enlarge
   The 64 metre radio telescope at Parkes Observatory
   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)
   Enlarge
   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)

   A radio telescope is a form of radio receiver used in astronomy. In
   contrast to an "ordinary" telescope, which receives visible light, 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 largest individual radio telescope is the RATAN-600 (Russia) with
   576 meter diameter of circular antenna ( RATAN-600 description). Other
   two individual radio telescopes at Pushchino Radio Astronomy
   Observatory, Russia, designed specially for the low frequency
   observations, are between the largest in their class. LPA ( LPA
   description (in Russian)) is 187 x 384 m size phased array meridional
   radio telescope, and DKR-1000 is 1000 x 1000 m cross radio telescope (
   DKR-1000 description (in Russian) ). 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.
   Other well known disk radio telescopes include the Arecibo radio
   telescope located in Arecibo, Puerto Rico, which is steerable within
   about 20° of the zenith, and the fully steerable Lovell telescope at
   Jodrell Bank in the United Kingdom . 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.

   An example of the array-type radio telescope is the Very Large Array
   (VLA), in Socorro, New Mexico, which is an interferometric array formed
   from 27 individual antennas. 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 25 000 small antennas over
   an area several hundreds of kilometres in diameter.

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

   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 the primary means to track space probes (see
   Deep Space Network), and are used in the SETI project.

Beginnings

   Nikola Tesla in the Colorado Springs lab recorded cosmic waves emitting
   from interstellar clouds and red giant stars. He observed repeating
   signals conducted by his transceiver. He announced that he received
   extraterrestrial radio signals. Tesla stated that he received signals
   from planets in some of the scientific journals of the time. The
   scientific community did not believe him, primarily because research of
   cosmic signals did not exist (what is known today as radio astronomy),
   and the community of science rejected Tesla's data. Tesla spent the
   latter part of his life trying to signal Mars.

   One of the earliest modern investigations into extraterrestrial sources
   of radio waves were by Karl Guthe Jansky, an engineer with Bell
   Telephone Laboratories, in the early 1930s. The first object actually
   detected was the centre of the Milky Way, followed by the sun. 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. After World War II, substantial
   improvements in radio astronomy technology were made by astronomers in
   Europe, Australia and the United States, and the field of radio
   astronomy began to blossom.

   One of the most notable developments came in 1946 with the introduction
   of radio interferometry (see, for example, Nature 158 pp 339 1946) by
   Martin Ryle's group in Cambridge (who obtained a nobel prize for this
   and later aperture synthesis work), also the Lloyd's mirror
   interferometer developed independently in 1946 by Joseph Pawsey's group
   at the University of Sydney (see Nature 157 pp 158 1946).

   See also: History of astronomical interferometry

   Retrieved from " http://en.wikipedia.org/wiki/Radio_telescope"
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   with only minor checks and changes (see www.wikipedia.org for details
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