Editing Radio telescope (section)

==Types==
[[File:Ooty_Radio_Telescope.jpg|thumb|upright=0.8|[[Ooty Radio Telescope|Ooty radio telescope]], a 326.5&nbsp;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&nbsp;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]].<ref name="galaxy196506">{{Cite magazine
 |last1=Ley
 |first1=Willy
 |last2=Menzel
 |first2=Donald H.
 |last3=Richardson
 |first3=Robert S.
 |date=June 1965
 |title=The Observatory on the Moon
 |department=For Your Information
 |url=https://archive.org/stream/Galaxy_v23n05_1965-06#page/n131/mode/2up
 |magazine=Galaxy Science Fiction
 |pages=132–150
}}</ref>
<ref>{{cite web|title=The Dish turns 45|url=http://www.csiro.au/files/files/pbhq.rtf|author=CSIRO|access-date=October 16, 2008|publisher=[[Commonwealth Scientific and Industrial Research Organisation]]|url-status=dead |archive-url=https://web.archive.org/web/20080824003225/http://www.csiro.au/files/files/pbhq.rtf |archive-date=August 24, 2008 }}</ref> At shorter wavelengths [[parabolic antenna|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&nbsp;cm (100&nbsp;MHz to 1&nbsp;GHz) are usually well over 100 meters in diameter. Telescopes working at wavelengths shorter than 30&nbsp;cm (above 1&nbsp;GHz) range in size from 3 to 90 meters in diameter.{{citation needed|date=August 2016}}<!-- unclear if this is original research or not; how many radio telescopes are there that are >90m in diameter?  If only one, or a few, then the prose statement here does not make sense.  "usually"? -->

===Frequencies===
The increasing use of radio frequencies for communication makes astronomical observations more and more difficult (see [[open spectrum#Radio astronomy needs|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.
[[File:Atmospheric electromagnetic opacity.svg|thumb|upright=1.8|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:
* Every frequency in the [[United States National Radio Quiet Zone]]
* [[Channel 37]]: 608 to 614&nbsp;MHz
* The "[[Hydrogen line]]", also known as the "21 centimeter line": 1,420.40575177&nbsp;MHz, used by many radio telescopes including [[The Big Ear]] in its discovery of the [[Wow! signal]]
* 1,406&nbsp;MHz and 430&nbsp;MHz <ref>{{cite web|url=http://www.jb.man.ac.uk/~pulsar/Education/Tutorial/tut/node115.html |title=Microstructure |website=Jb.man.ac.uk |date=1996-02-05 |access-date=2016-02-24}}</ref>
* The [[Waterhole (radio)|Waterhole]]: 1,420 to 1,666&nbsp;MHz
* The [[Arecibo Observatory]] had several receivers that together covered the whole 1–10&nbsp;GHz range.
* The [[Wilkinson Microwave Anisotropy Probe]] mapped the [[cosmic microwave background radiation]] in 5 different frequency bands, centered on 23&nbsp;GHz, 33&nbsp;GHz, 41&nbsp;GHz, 61&nbsp;GHz, and 94&nbsp;GHz.

===Big dishes===
{{comparison_FAST_Arecibo_Observatory_profiles.svg}}

The world's largest filled-aperture (i.e. full dish) radio telescope is the [[Five-hundred-meter Aperture Spherical Telescope]] (FAST) completed in 2016 by [[People's Republic of China|China]].<ref>{{cite web|url=http://english.peopledaily.com.cn/90001/90776/90881/6562884.html |title=China Exclusive: China starts building world's largest radio telescope |website=English.peopledaily.com.cn |date=2008-12-26 |access-date=2016-02-24}}</ref> The {{convert|500|m|ft|sp=us|adj=mid|-diameter}} dish with an area as large as 30 football fields is built into a natural [[karst]] depression in the landscape in [[Guizhou province]] and cannot move; the [[Antenna feed|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&nbsp;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&nbsp;meters. Construction began in 2007 and was completed July 2016<ref>{{cite web|url=http://www.space.com/33357-china-largest-radio-telescope-alien-life.html |title=China Finishes Building World's Largest Radio Telescope |website=[[Space.com]] |date=2016-07-06 |access-date=2016-07-06}}</ref> and the telescope became operational September 25, 2016.<ref>{{citation|last=Wong|first=Gillian|title=China Begins Operating World's Largest Radio Telescope|publisher=ABC News|date=25 September 2016|url=https://abcnews.go.com/Technology/wireStory/china-begins-operating-worlds-largest-radio-telescope-42339475}}</ref>

The world's second largest filled-aperture telescope was the [[Arecibo radio telescope]] located in [[Arecibo, Puerto Rico]], though it suffered catastrophic collapse on 1 December 2020. Arecibo was one of the world's few radio telescope also capable of active (i.e., transmitting) [[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 {{convert|305|m|ft|abbr=on}} 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 [[antenna feed|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 [[RATAN-600]] located near [[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.<ref name="Ridpath2012">{{cite book|last=Ridpath|first=Ian|title=A Dictionary of Astronomy|url=https://books.google.com/books?id=O31j9UJ3U4oC&pg=PA139|year=2012|publisher=OUP Oxford|isbn=978-0-19-960905-5|page=139}}</ref> 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 {{convert|110|m|ft|abbr=on}}, 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.

====Gallery of big dishes====
<gallery mode="packed" heights="200px">
File:FastTelescope*8sep2015.jpg|alt=Five-hundred-meter Aperture Spherical Telescope under construction|The 500 meter [[Five-hundred-meter Aperture Spherical Telescope]] (FAST), under construction, China (2016)
<!--File:|alt=Qitai Radio Telescope|The 110 meter [[Qitai Radio Telescope|Qitai]], China, (planned)-->
File:GBT.png|alt=Green Bank Telescope|The 100 meter<!--by 110m--> [[Green Bank Telescope]], Green Bank, West Virginia, US, the largest fully steerable radio telescope dish (2002)
File:DSCN6149_Effelsberg_totale.jpg|alt=Effelsberg 100-m Radio Telescope|The 100 meter [[Effelsberg 100-m Radio Telescope|Effelsberg]], in Bad Münstereifel, Germany (1971)
File:Lovell Telescope 5.jpg|alt=Lovell Telescope|The 76 meter [[Lovell Telescope|Lovell]], Jodrell Bank Observatory, England (1957)
File:Goldstone DSN antenna.jpg|alt=DSS 14 "Mars" antenna at Goldstone Deep Space Communications Complex|The 70 meter DSS 14 "Mars" antenna at [[Goldstone Deep Space Communications Complex]], Mojave Desert, California, US (1958)
File:70-м антенна П-2500 (РТ-70).jpg|alt=Yevpatoria RT-70 radio telescope|The 70 meter [[Yevpatoria RT-70 radio telescope|Yevpatoria RT-70]], Crimea, first of three [[RT-70]] in the former Soviet Union, (1978)<!--remove RT-70 list when image of third used-->
File:Антенна П-2500 (РТ-70) ВЦДКС - panoramio (2).jpg|The 70 meter [[Galenki RT-70 radio telescope|Galenki RT-70]], Galenki, Russia, second of three [[RT-70]] in the former Soviet Union, (1984)<!--remove RT-70 list when image of third used-->
<!--File:|alt=Suffa RT-70 radio telescope under construction|The 70 meter [[Suffa RT-70 radio telescope|Suffa RT-70]], Suffa plateau, Uzbekistan, third of three [[RT-70]] in the former Soviet Union, (under construction)--><!--remove RT-70 list when image of third used-->
</gallery>

===Radio Telescopes in space===
{{Update section|date=October 2024}}
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]].
{{gallery|mode=packed
| title    = Space radiotelescopes
|File:Rus Stamp GSS-Lyahov-Rumin.jpg|KRT-10 dish of a [[Salyut-6]] on a stamp
|File:Haruka HALCA VSOP MUSES-B deployment test.jpg|Japanese [[HALCA]] dish
|File:RIAN archive 930415 Russian Spektr R space-born radio telescope.jpg|Assembled [[Spektr-R]] dish (left)
}}