Radio telescope

Source: Wikipedia, the free encyclopedia.
The 64-meter radio telescope at Parkes Observatory as seen in 1969, when it was used to receive live televised video from Apollo 11
UTR-2 low frequency radio telescope, Kharkiv region, Ukraine. Consists of an array of 2040 cage dipole
elements.

A radio telescope is a specialized

optical astronomy
. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night.

Since astronomical radio sources such as planets, stars, nebulas and galaxies are very far away, the radio waves coming from them are extremely weak, so radio telescopes require very large antennas to collect enough radio energy to study them, and extremely sensitive receiving equipment. Radio telescopes are typically large parabolic ("dish") antennas similar to those employed in tracking and communicating with satellites and space probes. They may be used individually or linked together electronically in an array. Radio observatories are preferentially located far from major centers of population to avoid electromagnetic interference (EMI) from radio, television, radar, motor vehicles, and other man-made electronic devices.

Radio waves from space were first detected by engineer

Holmdel, New Jersey using an antenna built to study radio receiver noise. The first purpose-built radio telescope was a 9-meter parabolic dish constructed by radio amateur Grote Reber in his back yard in Wheaton, Illinois
in 1937. The sky survey he performed is often considered the beginning of the field of radio astronomy.

Early radio telescopes

Full-size replica of the first radio telescope, Jansky's dipole array of 1932, preserved at the US Green Bank Observatory in Green Bank, West Virginia.
Reber's "dish" radio telescope, Wheaton, Illinois, 1937

The first radio antenna used to identify an astronomical radio source was built by

Milky Way Galaxy and was strongest in the direction of the center of the galaxy, in the constellation of Sagittarius
.

An amateur radio operator,

very high radio frequencies, discovering other radio sources. The rapid development of radar during World War II created technology which was applied to radio astronomy after the war, and radio astronomy became a branch of astronomy, with universities and research institutes constructing large radio telescopes.[4]

Types

Ooty radio telescope, a 326.5 MHz dipole array in Ooty, India

The range of frequencies in the electromagnetic spectrum that makes up the radio spectrum is very large. As a consequence, the types of antennas that are used as radio telescopes vary widely in design, size, and configuration. At wavelengths of 30 meters to 3 meters (10–100 MHz), they are generally either directional antenna arrays similar to "TV antennas" or large stationary reflectors with movable focal points. Since the wavelengths being observed with these types of antennas are so long, the "reflector" surfaces can be constructed from coarse wire mesh such as chicken wire.[5] [6] At shorter wavelengths parabolic "dish" antennas predominate. The angular resolution of a dish antenna is determined by the ratio of the diameter of the dish to the wavelength of the radio waves being observed. This dictates the dish size a radio telescope needs for a useful resolution. Radio telescopes that operate at wavelengths of 3 meters to 30 cm (100 MHz to 1 GHz) are usually well over 100 meters in diameter. Telescopes working at wavelengths shorter than 30 cm (above 1 GHz) range in size from 3 to 90 meters in diameter.[citation needed]

Frequencies

The increasing use of radio frequencies for communication makes astronomical observations more and more difficult (see Open spectrum). Negotiations to defend the frequency allocation for parts of the spectrum most useful for observing the universe are coordinated in the Scientific Committee on Frequency Allocations for Radio Astronomy and Space Science.

Plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation.

Some of the more notable frequency bands used by radio telescopes include:

Big dishes

Comparison of the Arecibo (top), FAST (middle) and RATAN-600 (bottom) radio telescopes at the same scale

The world's largest filled-aperture (i.e. full dish) radio telescope is the

Guizhou province and cannot move; the feed antenna is in a cabin suspended above the dish on cables. The active dish is composed of 4,450 moveable panels controlled by a computer. By changing the shape of the dish and moving the feed cabin on its cables, the telescope can be steered to point to any region of the sky up to 40° from the zenith. Although the dish is 500 meters in diameter, only a 300-meter circular area on the dish is illuminated by the feed antenna at any given time, so the actual effective aperture is 300 meters. Construction began in 2007 and was completed July 2016[9] and the telescope became operational September 25, 2016.[10]

The world's second largest filled-aperture telescope was the

radar imaging of near-Earth objects (see: radar astronomy); most other telescopes employ passive detection, i.e., receiving only. Arecibo was another stationary dish telescope like FAST. Arecibo's 305 m (1,001 ft) dish was built into a natural depression in the landscape, the antenna was steerable within an angle of about 20° of the zenith by moving the suspended feed antenna
, giving use of a 270-meter diameter portion of the dish for any individual observation.

The largest individual radio telescope of any kind is the

Nizhny Arkhyz, Russia
, which consists of a 576-meter circle of rectangular radio reflectors, each of which can be pointed towards a central conical receiver.

The above stationary dishes are not fully "steerable"; they can only be aimed at points in an area of the sky near the zenith, and cannot receive from sources near the horizon. The largest fully steerable dish radio telescope is the 100 meter Green Bank Telescope in West Virginia, United States, constructed in 2000. The largest fully steerable radio telescope in Europe is the Effelsberg 100-m Radio Telescope near Bonn, Germany, operated by the Max Planck Institute for Radio Astronomy, which also was the world's largest fully steerable telescope for 30 years until the Green Bank antenna was constructed.[11] The third-largest fully steerable radio telescope is the 76-meter Lovell Telescope at Jodrell Bank Observatory in Cheshire, England, completed in 1957. The fourth-largest fully steerable radio telescopes are six 70-meter dishes: three Russian RT-70, and three in the NASA Deep Space Network. The planned Qitai Radio Telescope, at a diameter of 110 m (360 ft), is expected to become the world's largest fully steerable single-dish radio telescope when completed in 2028.

A more typical radio telescope has a single antenna of about 25 meters diameter. Dozens of radio telescopes of about this size are operated in radio observatories all over the world.

Radio Telescopes in space

Since 1965, humans have launched three space-based radio telescopes. The first one, KRT-10, was attached to Salyut 6 orbital space station in 1979. In 1997, Japan sent the second, HALCA. The last one was sent by Russia in 2011 called Spektr-R.

Space radiotelescopes
  • KRT-10 dish of a Salyut-6 on a stamp
    KRT-10 dish of a
    Salyut-6
    on a stamp
  • Japanese HALCA dish
    Japanese HALCA dish
  • Assembled Spektr-R dish (left)
    Assembled Spektr-R dish (left)

Radio interferometry

Main article: Astronomical interferometer
See also: Radio astronomy § Radio interferometry
interferometric array
formed of 27 parabolic dish telescopes.

One of the most notable developments came in 1946 with the introduction of the technique called

interfering) the signal waves from the different telescopes on the principle that waves that coincide with the same phase
will add to each other while two waves that have opposite phases will cancel each other out. This creates a combined telescope that is equivalent in resolution (though not in sensitivity) to a single antenna whose diameter is equal to the spacing of the antennas furthest apart in the array.

sub-millimeter wavelengths

A high-quality image requires a large number of different separations between telescopes. Projected separation between any two telescopes, as seen from the radio source, is called a baseline. For example, the

Cosmic Microwave Background, like the CBI
interferometer in 2004.

The world's largest physically connected telescope, the Square Kilometre Array (SKA), is planned to start operations in 2027, [15] Although the first stations had "first fringes" in 2024.[16]

Astronomical observations

Main article: Radio astronomy

Many astronomical objects are not only observable in

planets.[17][18]

See also

References

  1. ISBN 978-1498770194
    .
  2. ISBN 978-1593394929
    .
  3. ISBN 978-0387683607
    .
  4. ISBN 0-521-25485-X
  5. ^ Ley, Willy; Menzel, Donald H.; Richardson, Robert S. (June 1965). "The Observatory on the Moon". For Your Information. Galaxy Science Fiction. pp. 132–150.
  6. Commonwealth Scientific and Industrial Research Organisation. Archived from the original
    on August 24, 2008. Retrieved October 16, 2008.
  7. ^ "Microstructure". Jb.man.ac.uk. 1996-02-05. Retrieved 2016-02-24.
  8. ^ "China Exclusive: China starts building world's largest radio telescope". English.peopledaily.com.cn. 2008-12-26. Retrieved 2016-02-24.
  9. ^ "China Finishes Building World's Largest Radio Telescope". Space.com. 2016-07-06. Retrieved 2016-07-06.
  10. ^ Wong, Gillian (25 September 2016), China Begins Operating World's Largest Radio Telescope, ABC News
  11. ISBN 978-0-19-960905-5
    .
  12. ^ "Microwave Probing of the Invisible". Archived from the original on August 31, 2007. Retrieved June 13, 2007.
  13. ^ Nature vol.158, p. 339, 1946.
  14. ^ Nature vol.157, p. 158, 1946.
  15. ^ "New Zealand pulls out of the Square Kilometre Array after benefits questioned". Physics World. IOP Publishing. 4 July 2019. Archived from the original on 4 July 2019. Retrieved 5 July 2019.
  16. ^ Wiegert, Theresa (2024-09-24). "SKA telescope gets its '1st fringes'". earthsky.org. Retrieved 2025-02-22.
  17. ^ "What is Radio Astronomy?". Public Website.
  18. ^ "What are Radio Telescopes?".

Further reading

Wikimedia Commons has media related to Radio telescopes.
  • Rohlfs, K., & Wilson, T. L. (2004). Tools of radio astronomy. Astronomy and astrophysics library. Berlin, Germany: Springer.
  • ISBN 0-8038-9347-7
    .
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