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Radio astronomy uses radio telescopes to hear the universe.

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Radio astronomy is the study of celestial phenomena through measurement of radio waves emitted by physical processes occurring in space and the universe. Radio waves have a much greater wavelength than light waves. In order to receive signals with large signal-to-noise ratio, radio astronomy requires a large antenna or an array of smaller antennas working together (for example, the Very Large Array). Most of these Radio telescopes use a parabolic dish to reflect the waves to a receiver which detects and amplifies the signal into usable data. This allows astronomers to see a region of the radio sky. If they take multiple scans of overlapping strips of the sky they can piece together an image ('mosaicing'). Radio astronomy is a relatively new field of astronomical research that still has much more to be discovered.

Radio astronomy: astronomical sources.

Radio Astronomy Observatory.
A 151 MHz map of the region: 140º to 180º galactic longitude; -5º to 5º galactic latitude from the CLFST at the Mullard Radio Astronomy Observatory. Just like in the visible, at low radio frequencies the sky is dominated by small bright sources, but the sources are typically active galaxies and supernova remnants rather than stars.

Radio astronomy has led to substantial increases in astronomical knowledge, particularly with the discovery of several classes of new objects, including pulsars, quasars and radio galaxies. This is because radio astronomy allows us to see things that are not detectable in optical astronomy. Such objects represent some of the most extreme and energetic physical processes in the universe.

Radio astronomy is also partly responsible for the idea that Dark matter is an important component of our universe; radio measurements of the rotation of galaxies suggest that there is much more mass in galaxies than has been directly observed (see Vera Rubin). The cosmic microwave background radiation was also first detected using radio telescopes. However, radio telescopes have also been used to investigate objects much closer to home, including observations of the Sun and solar activity, and radar mapping of the planets.

Radio astronomy: other sources include:

  • Active galactic nuclei and pulsars have jets of charged particles which emit synchrotron radiation.
  • Merging galaxy clusters often show diffuse radio emission.
  • Supernova remnants can also show diffuse radio emission.
  • The Cosmic microwave background is blackbody radio emission.

Observational techniques of Radio astronomy.

Radio telescopes can now be found all over the world (see List of radio telescopes). Most are designed for microwave radiation. Widely separated telescopes are often combined using a technique called interferometry in order to obtain observations with much higher resolution than could be obtained using a single receiver. Initially telescopes within a few kilometers of each other were combined (see, for example, the Mullard Radio Astronomy Observatory), but since the 1970s telescopes from all over the world (and even in Earth orbit) have been combined to perform Very Long Baseline Interferometry.

The United States government has established an institution to conduct radio astronomy research in the US, titled the National Radio Astronomy Observatory (commonly abbreviated as NRAO). This institution controls various radio telescopes around the United States included the world's largest fully mobile radio telescope, the Green Bank Telescope. The United States government has also set aside a national radio quiet zone for radio astronomy research centered around Green Bank, West Virginia. As a result, Green Bank is now the home of NRAO's primary facility.

Historical development of radio astronomy.

Modern radio astronomy started with a serendipitous discovery by Karl Guthe Jansky, an engineer with Bell Telephone Laboratories, in the early 1930s. Jansky was investigating static that interfered with short wave voice transmissions using a turntable mounted 100 ft. by 20 ft. directional antenna working at a frequency of 20.5 MHz (wavelength about 14.6 meters). By rotating the antenna the direction of a received "static" could be pinpointed. A small shed to the side of the antenna housed an analog pen-and-paper recording system. After sorting out signals from nearby and distant thunderstorms, Jansky continued to investigate a faint steady hiss of unknown origin. Jansky finally determined that the signal repeated on a cycle of 23 hours and 56 minutes. This four-minute lag is typical of an astronomical source "fixed" on the celestial sphere rotating in sync with sidereal time. By comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way and was strongest in the direction of the center the galaxy, in the constellation of Sagittarius.

Grote Reber helped pioneer radio astronomy when he built the first parabolic "dish" radio telescope (9m in diameter) in 1937. He was instrumental in repeating Karl Guthe Jansky's pioneering but somewhat simple work, and went on to conduct the first sky survey in the radio frequencies. On February 27, 1942, J.S. Hey, a British Army research officer, helped progress radio astronomy further, when he discovered that the sun emitted radio waves. 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 the technique called astronomical interferometry where many radio telescopes are combined in a large array to achieve much higher resolutions. Martin Ryle's group in Cambridge obtained a Nobel Prize for this and later Aperture synthesis work. The Lloyd's mirror interferometer was also developed independently in 1946 by Joseph Pawsey's group at the CSIR, (later CSIRO) in Sydney. In the early 1950s the Cambridge Interferometer mapped the radio sky to produce the famous 2C and 3C surveys of radio sources. Two issues, one astronomical and one technical, dominated the research in Cambridge, from the late 1940's for more than thirty years. What was the nature of the discrete radio sources, or `radio stars'? Where were they, what were they, what were their properties, how many were there, how did they work and what was their significance in the Universe? Of parallel importance was the puzzle of how to devise new kinds of radio telescope which would elucidate these astronomical questions.

Earliest observation with radio astronomy.

In 1899, the eccentric Nikola Tesla, in accord with many other plans of his, planned to build a tower in a experimental station at Colorado topped by a copper ball that he would turn into a sensitive Radio telescope. While investigating atmospheric electricity in 1900, Tesla noted repetitive signals that he deduced must be coming from a non-terrestrial source. Although Tesla mistook this to be radio communication from intelligent beings living on Venus or Mars it may have been the earliest observation of an astronomical radio source (A 1996 analysis indicated Tesla may have been observing Jovian plasma torus signals).

Radio astronomy extra pages.

Giant Magellan Telescope.

Oct 28, 2005 Workers at the University of Arizona Steward Observatory Mirror Lab have cast the first mirror for the Giant Magellan Telescope. By the time they're complete, the lab will cast a total of 7 of these enormous 8.4-metre (27-foot) mirrors, giving the enormous observatory the equivalent of a 22-metre aperture. The Giant Magellan telescope will be constructed in Northern Chile by 2016.

Links For Radio Astronomy.

Jupiter Space Station Radio Observatory - The JSS is a radio astronomy experimental research group working in solar physics as well as hydrogen and methanol radio emissions.
Make More Miles on VHF - Information / hotlinks for VHF radio amateurs/ VHF weak signal / meteorscatter, listing of amateur radio stations qrv for meteorscatter
Project S.T.R.A.T. Earth Station One - Project S.T.R.A.T. (Special Telemetry Research and Tracking) was established in the spring of 1972. By the summer of 1972 the first ulf (ultra-Low Frequency, 40 hertz to 15 kilohertz) radio marker beacon started broadcasting a 150-watt ulf sequence of el
Radio-Sky Publishing - Radio astronomy resources for teachers, students, and amateurs.
Society of Amateur Radio Astronomers - a dedicated group of people that formed an international society to learn, trade technical information and do their own observations of the radio sky.
University of Alberta Radio Astronomy Group
VE3EAP's Home Page - Amateur Radio Directory: information, frequency listings, & personal stuff about VE3EAP. Designed for IE
Ventspils International Radio Astronomy Center - VIRAC - a space information center. Main instruments: 32m and 16m fully steerable radiotelescopes, geodynamical station (LV-04 Irbene).
Alaska SAR Facility's Homepage
Amateur Radio Astronomy
Arecibo Observatory
Berkeley Illinois Maryland Association
Big Ear Radio Telescope
Bologna Institute of Radioastronomy
CAT homepage
Cygnus-Quasar Books
Hartebeesthoek Radio Astronomy
Institut de RadioAstronomie Millimétrique
Jodrell Bank
Large Millimeter and Sub Millimeter Array
Max Planck Institute for Radio Astronomy
Metsahovi Radio Astronomy
National Center for Radio Astrophysics
National Radio Astronomy Observatory
NFRA Homepage
Nobeyama Radio Observatory
OVRO Homepage
Pisgah Astronomical Research Institute
Space Very Long Baseline Interferometry Project
University of Calgary Radio Astronomy Page
University of Tasmania - Radio Astronomy Group

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