Editing Karl Guthe Jansky (section)

== Radio astronomy ==
[[File:JanskyatAntenna hi.tif|thumb|Jansky and his rotating directional radio antenna (early 1930s), the world's first radio telescope.]]
<!-- Deleted image removed: [[File:Karl Guthe Jansky radio telescope.jpeg|thumb|right|Karl Jansky makes adjustments to his antenna, used to identify radio waves from outer space for the first time.]]  -->
At Bell Telephone Laboratories, Jansky built a [[directional antenna]] designed to receive radio waves at a [[frequency]] of 20.5 [[megaHertz|MHz]] (wavelength about 14.6 meters). It had a diameter of approximately 100&nbsp;ft. (30 meters) and stood 20&nbsp;ft. (6 meters) tall. It was mounted on top of a turntable on a set of four Ford [[Model-T]] wheels, which allowed it to be rotated in the azimuthal direction, earning it the nickname "Jansky's merry-go-round" (the cost of which was later estimated to be less than $1000).<ref name="50th" />{{rp|vii}}  By rotating the antenna, the direction of a received signal could be pinpointed. The intensity of the signal was recorded by an [[analog signal|analog]] pen-and-paper recording system housed in a small shed to the side of the antenna.<ref name="kraus 1981">{{cite web |last1=Kraus |first1=John |title=The First 50 Years of Radio Astronomy, Part 1: Karl Jansky and His Discovery of Radio Waves from Our Galaxy |url=http://www.bigear.org/CSMO/HTML/CS12/cs12p08.htm |publisher=North American AstroPhysical Observatory (NAAPO). Cosmic Search, Vol. 3, No. 4 |access-date=21 September 2021 |date=Fall 1981 |quote=In 1930 essentially all that we knew about the heavens had come from what we could see or photograph. Karl Jansky changed all that. A universe of radio sounds to which mankind had been deaf since time immemorial now suddenly burst forth in full chorus.}}</ref>

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 static or "hiss" of unknown origin. He spent over a year investigating the source of the third type of static. The location of maximum intensity rose and fell once a day, leading Jansky to surmise initially that he was detecting radiation from the Sun.

After a few months of following the signal, however, the point of maximum static moved away from the position of the Sun. Jansky also determined that the signal repeated on a cycle of 23 hours and 56 minutes. Jansky discussed the puzzling phenomena with his friend the astrophysicist Albert Melvin Skellett, who pointed out that the observed time between the signal peaks was the exact length of a [[sidereal time|sidereal day]]; the time it took for "fixed" astronomical objects, such as a star, to pass in front of the antenna every time the Earth rotated.<ref name="bookrags.com">{{cite book | url = http://www.bookrags.com/biography/karl-jansky-wsd/ | title = World of Scientific Discovery on Karl Jansky | access-date = 2010-04-09}}</ref> By comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the [[Milky Way]] and was strongest (7:10 p.m. on September 16, 1932) in the direction of the center of the galaxy, in the [[constellation]] of [[Sagittarius (constellation)|Sagittarius]].

Jansky announced his discovery at a meeting in Washington D.C. in April 1933 to a small audience who could not comprehend its significance.<ref>{{Citation |editor-first=W. T. |editor-last=Sullivan |title=The Early Years of Radio Astronomy: Reflections Fifty Years After Jansky's Discovery |publisher=Cambridge University Press |year=1984 |isbn=978-0-521-61602-7 }}</ref> His discovery was widely publicized, appearing in the ''[[New York Times]]'' of May 5, 1933,<ref>{{cite news | author = Smothers, Ronald | title = Commemorating a Discovery in Radio Astronomy |date = June 9, 1998 |work = [[New York Times]] | url = https://query.nytimes.com/gst/fullpage.html?res=9804E3DE153AF93AA35755C0A96E958260 | access-date = 2008-08-14}}</ref> and he was interviewed on a special NBC program on "Radio sounds from among the stars".<ref name="kraus 1981" /> In October 1933, his discovery was published in a journal article entitled "Electrical disturbances apparently of extraterrestrial origin" in the ''[[Proceedings of the Institute of Radio Engineers]]''.<ref>{{cite journal |last1=Karl Jansky |title=Electrical Disturbances Apparently of Extraterrestrial Origin |journal=Proceedings of the Institute of Radio Engineers |date=Oct 1933 |volume=21 |issue=10 |pages=1387–1398 |doi=10.1109/JRPROC.1933.227458|url=https://ieeexplore.ieee.org/document/681378}} See also {{cite journal |last1=Karl Jansky |title=Radio Waves from Outside the Solar System |journal=Nature |date=Jul 8, 1933 |volume=132 |issue=3323 |page=66 |doi=10.1038/132066a0 |bibcode=1933Natur.132...66J |s2cid=4063838 |url=https://www.nature.com/articles/132066a0.pdf}}</ref>

If the radio sources were from the stars, the Sun should also be producing radio noise, but Jansky found that it did not. In the early 1930s, the Sun was at an inactive phase in its sunspot cycle. In 1935 Jansky made the suggestion that the strange radio signals were produced from interstellar gas, in particular, by "thermal agitation of charged particles."<ref name="bookrags.com" /> Jansky accomplished these investigations while still in his twenties with a bachelor's degree in physics.

Jansky wanted to further investigate the Milky Way radio waves after 1935 (he called the radiation "Star Noise" in the thesis he submitted to earn his 1936 University of Wisconsin Masters degree),<ref name="MagL-Jansky">{{cite web |title=Karl Jansky |url=https://nationalmaglab.org/education/magnet-academy/history-of-electricity-magnetism/pioneers/karl-jansky |website=MagLab |publisher=National High Magnetic Field Laboratory. |access-date=17 June 2022}}</ref><ref>{{cite web |title=Jansky, Karl (1905–1950) |url=https://www.encyclopedia.com/people/science-and-technology/electrical-engineering-biographies/karl-jansky |website=Encyclopedia.com |access-date=17 June 2022 |date=17 May 2018}}</ref> but he found little support from either astronomers, for whom it was completely foreign, or Bell Labs, which could not justify, during the [[Great Depression]], the cost of research on a phenomenon that did not significantly affect trans-Atlantic communications systems.