Radio astronomy
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Microwave image of 3C353 galaxy at 8.4 GHz (36 mm). The overall linear size of the radio structure is 120 kpc. |
Radio astronomy is the study of celestial phenomena through measurement of the characteristics of
radio waves emitted by physical processes occurring in space. Radio waves are much longer than
light waves. In order to receive good signals, radio astronomy requires large antennas, or arrays of smaller antennas all working together (The
Very Large Array near Socorro, New Mexico is an example of this). Most
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 overlaping 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.
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 center of the
Milky Way, followed by the
sun. These early discoveries were confirmed by
Grote Reber by 1938. After
World War II, substantial improvements in radio astronomy technology were made by astronomers in Australia, Europe 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
CSIR, later CSIRO in Sydney (see Nature 157 pp 158 1946). 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.
See also:
*
History of astronomical interferometry |
A 151 MHz map of the region: 140° to 180° galactic longitude; -5° to 5° 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 remnents 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 telescopes can now be found all over the world (see
List of radio telescopes). 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 kilometres 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.
See also:*
Very Long Baseline Interferometry*
Aperture synthesis*
Active galactic nuclei and
pulsars have jets of charged particles which emit
synchrotron radiation* Merging
galaxy clusters often show diffuse radio emission[
1]
*
Supernova remnants can also show diffuse radio emission
* The
Cosmic microwave background is
blackbody radio emission
*
History of Radio AstronomyHistory of Radio Astronomy
*
The History of the Nancay Radio Observatory - a history of
French radio astronomy
*
Reber Radio Telescope - National Park Services
*
The History of Radio Astronomy -
Haystack Observatory,
MIT*
History of High-Resolution Radio Astronomy published in the Annual Review of Astronomy and Astrophysics, September 2001*
Radio Telescope Developed - a brief history from
NASA Goddard Space Flight Center* Hanes, Dave,
"Physics 014: The Course Notes, Radio Astronomy". Astronomy Group and Department of Physics, Queen's University. 2000-2001.
