Radio astronomy

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 telescopes use a parabolic dish to reflect the waves to a reciever which detecs and amplifies the signal into usable data. This allows astronomers to see a strip of the radio sky. If they take multiple scans of overlaping strips of the sky they can piece together an image using a false color technique. Radio astronomy is a relatively new field of astronomical research that still has much more to be discovered.

History

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 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 e.g. 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).

Developments

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 thing 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 e.g. 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

Sources of radio emission

• Active galactic nucleii and pulsars have jets of charge particles which emit synchrotron radiation
• The Cosmic microwave background is blackbody radio emission

External links

• History of Radio Astronomy (http://www.nrao.edu/whatisra/history.shtml)History of Radio Astronomy
• The History of the Nancay Radio Observatory (http://www.obs-nancay.fr/usn/a_histor.htm) - a history of French radio astronomy
• Reber Radio Telescope (http://www.cr.nps.gov/history/online_books/butowsky5/astro4o.htm) - National Park Services
• The History of Radio Astronomy (http://web.haystack.mit.edu/education/radiohist.html) - Haystack Observatory, MIT
• History of High-Resolution Radio Astronomy published in the Annual Review of Astronomy and Astrophysics, September 2001 (http://arjournals.annualreviews.org/doi/full/10.1146/annurev.astro.39.1.457?cookieSet=1)
• Radio Telescope Developed (http://edmall.gsfc.nasa.gov/aacps/news/Radio_Telescope.html) - a brief history from NASA Goddard Space Flight Center
• Hanes, Dave, "Physics 014: The Course Notes, Radio Astronomy (http://www.astro.queensu.ca/~hanes/p014/Notes/Topic_048.html)". Astronomy Group and Department of Physics, Queen's University. 2000-2001.bg:Радиоастрономия

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