Radio telescope
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 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. 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 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) |
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.
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.
Grote Reber (December 22, 1911 â€" 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*
Radio astronomy*
Aperture synthesis*
Complete list of radio telescopes on Wikipedia* Alternative, smaller
list of radio telescopes
