Editing Radio telescope (section)

==Early radio telescopes==
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| image1   = Janksy Karl radio telescope.jpg
| caption1 = Full-size replica of the first radio telescope, Jansky's [[dipole antenna|dipole]] array of 1932, preserved at the US [[Green Bank Observatory]] in Green Bank, West Virginia.
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| image2   = Grote Antenna Wheaton.gif
| caption2 = [[Grote Reber|Reber]]'s "dish" radio telescope, Wheaton, Illinois, 1937
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The first radio antenna used to identify an astronomical radio source was built by [[Karl Guthe Jansky]], an engineer with [[Bell Labs|Bell Telephone Laboratories]], in 1932. Jansky was assigned the task of identifying sources of [[static (radio)|static]] that might interfere with [[radiotelephone]] service. Jansky's antenna was an array of [[dipole]]s and [[Reflector (antenna)|reflectors]] designed to receive [[short wave]] radio signals at a [[frequency]] of 20.5 [[Megahertz|MHz]] (wavelength about 14.6 meters). It was mounted on a turntable that allowed it to rotate in any direction, earning it the name "Jansky's merry-go-round." It had a diameter of approximately {{convert|100|ft|m|-1|abbr=on}} and stood {{convert|20|ft|m|0|abbr=on}} tall. By rotating the antenna, the direction of the received interfering radio source (static) could be pinpointed. A small shed to the side of the antenna housed an [[Analog device|analog]] pen-and-paper recording system. After recording signals from all directions for several months, Jansky eventually categorized them into three types of static: nearby thunderstorms, distant thunderstorms, and a faint steady hiss above [[shot noise]], of unknown origin. Jansky finally determined that the "faint hiss" repeated on a cycle of 23 hours and 56 minutes. This period is the length of an astronomical [[sidereal day]], the time it takes any "fixed" object located on the [[celestial sphere]] to come back to the same location in the sky. Thus Jansky suspected that the hiss originated outside of the [[Solar System]], and by comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the [[Milky Way Galaxy]] and was strongest in the direction of the center of the galaxy, in the [[constellation]] of [[Sagittarius (constellation)|Sagittarius]].

An amateur radio operator, [[Grote Reber]], was one of the pioneers of what became known as [[radio astronomy]]. He built the first parabolic "dish" radio telescope, {{convert|9|m|ft|0}} in diameter, in his back yard in Wheaton, Illinois in 1937. He repeated Jansky's pioneering work, identifying the Milky Way as the first off-world radio source, and he went on to conduct the first sky survey at [[VHF|very high]] radio frequencies, discovering other radio sources. The rapid [[History of radar|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.<ref>Sullivan, W.T. (1984). ''The Early Years of Radio Astronomy''. Cambridge University Press. {{ISBN|0-521-25485-X}}</ref>