Editing Cosmic noise

{{Short description|Physical phenomenon from outside of the Earth's atmosphere}}
'''Cosmic noise''', also known as '''galactic radio noise''', is radio-frequency electromagnetic radiation from sources [[Outer space|outside of the Earth's atmosphere]]. Its characteristics are comparable to those of [[thermal noise]]. Cosmic noise occurs at frequencies above about 15&nbsp;[[Hertz|MHz]] when highly directional antennas are pointed toward the Sun or other regions of the sky, such as the [[Galactic Center|center of the Milky Way Galaxy]]. Celestial objects like [[quasar]]s, which are super dense objects far from Earth, emit electromagnetic waves in their full spectrum, including radio waves. The fall of a [[meteorite]] can also be heard through a radio receiver; the falling object burns from friction with the Earth's atmosphere, ionizing surrounding gases and producing [[radio waves]]. [[Cosmic microwave background radiation]] (CMBR) from [[outer space]] is also a form of cosmic noise. CMBR is thought to be a relic of the [[Big Bang]], and pervades the space almost homogeneously over the entire [[celestial sphere]]. The [[Bandwidth (signal processing)|bandwidth]] of the CMBR is wide, though the peak is in the microwave range.

== History ==
[[Karl Guthe Jansky|Karl Jansky]], an American physicist and radio engineer, first discovered [[radio wave]]s from the [[Milky Way]] in August, 1931. At [[Bell Labs|Bell Telephone Laboratories]] in 1932, Jansky built an antenna designed to receive radio waves at a frequency of 20.5&nbsp;[[Hertz|MHz]], which is a wavelength of approximately 14.6&nbsp;meters.

After recording signals with this antenna for several months, Jansky categorized them into three types: nearby thunderstorms, distant thunderstorms, and a faint steady hiss of an unknown origin. He discovered the location of maximum intensity rose and fell once a day, which led him to believe he was detecting radiation from the [[Sun]].

A few months went by following this signal thought to be from the Sun, and Jansky found that the brightest point moved away from the Sun and concluded the cycle repeated every 23 hours and 56 minutes. After this discovery, Jansky concluded the radiation was coming from the [[Milky Way]] and was strongest in the direction of the center of the [[galaxy]].

Jansky's work helped to distinguish between the radio sky and the [[Optics|optical]] sky. The optical sky is what is seen by the human eye, whereas the radio sky consists of daytime meteors, solar bursts, quasars, and gravitational waves.

Later in 1963, American physicist and radio astronomer [[Arno Allan Penzias]] (born April 26, 1933) discovered  [[Cosmic microwave background|cosmic microwave background radiation]]. Penzias's discovery of  cosmic microwave background radiation helped establish the [[Big Bang]] theory of cosmology. Penzias and his partner, [[Robert Woodrow Wilson]] worked together on ultra-sensitive cryogenic [[microwave]] receivers, originally intended for radio astronomy observations. In 1964, upon creating their most sensitive antenna/receiver system, the [[Holmdel Horn Antenna]], the two discovered a radio noise they could not explain. After further investigation, Penzias contacted [[Robert H. Dicke|Robert Dicke]], who suggested it could be the background radiation predicted by cosmological theories, a radio remnant of the [[Big Bang]]. Penzias and Wilson won the [[Nobel Prize in Physics]] in 1978.

=== NASA's work ===
The [[ARCADE|Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission]] (ARCADE) is a device designed to observe the transition out of the "cosmic dark ages" as the first stars ignite in nuclear fusion and the [[universe]] begins to resemble its current form.<ref>{{Cite web |title=ARCADE – Absolute Radiometer for Cosmology, Astrophysics, Diffuse Emission |url=https://asd.gsfc.nasa.gov/archive/arcade/ |access-date=2021-04-09 |website=asd.gsfc.nasa.gov}}</ref>

ARCADE consists of 7 precision [[radiometer]]s carried to an altitude of over 35&nbsp;km (21&nbsp;miles) by a [[Research balloon|scientific research balloon]]. The device measures the tiny heating of the early [[universe]] by the first generation of stars and galaxies to form after the [[Big Bang]].

== Sources of cosmic noise ==
Cosmic noise refers to the [[Radio frequency|background radio frequency]] radiation from [[Galaxy|galactic sources]], which have constant intensity during [[geomagnetic]]ally quiet periods.<ref name=":2">{{Cite journal |date=2018-06-01 |title=Solar flare induced cosmic noise absorption |journal=NRIAG Journal of Astronomy and Geophysics |language=en |volume=7 |issue=1 |pages=31–39 |doi=10.1016/j.nrjag.2018.03.002 |issn=2090-9977 |doi-access=free |last1=Ogunmodimu |first1=Olugbenga |last2=Honary |first2=Farideh |last3=Rogers |first3=Neil |last4=Falayi |first4=E. O. |last5=Bolaji |first5=O. S. |bibcode=2018JAsGe...7...31O}}</ref>

=== Sun flares ===
Cosmic noise can be traced from [[solar flares]], which are sudden explosive releases of stored [[magnetic energy]] in the atmosphere of the Sun, causing sudden brightening of the [[photosphere]]. Solar flares can last from a few minutes to several hours.

During solar flare events, particles and electromagnetic emissions can affect [[Earth]]'s atmosphere by fluctuating the level of [[ionization]] in the Earth's [[ionosphere]]. Increased ionization results in absorption of the cosmic radio noise as it passes through the ionosphere.

=== Solar wind ===
[[Solar wind]] is a flux of particles, [[proton]]s and [[electron]]s together with [[Atomic nucleus|nuclei]] of heavier elements in smaller numbers, that are accelerated by the high temperatures of the [[solar corona]] to velocities large enough to allow them to escape from the Sun's gravitational field.<ref>{{Cite web |title=Solar wind |url=https://www.britannica.com/science/solar-wind |access-date=2021-04-09 |website=Encyclopedia Britannica |language=en}}</ref>

Solar wind causes sudden bursts of cosmic noise absorption in the Earth's ionosphere. These bursts can only be detected only if the magnitude of the geomagnetic field perturbation caused by the solar wind shock is large enough.<ref>{{cite journal |last1=Osepian |first1=A. |last2=Kirkwood |first2=S. |title=Cosmic radio-noise absorption bursts caused by solar wind shocks |journal=Annales Geophysicae |date=7 September 2004 |volume=22 |issue=8 |pages=2973–2987 |doi=10.5194/angeo-22-2973-2004 |bibcode=2004AnGeo..22.2973O |s2cid=55842333 |url=https://angeo.copernicus.org/articles/22/2973/2004/angeo-22-2973-2004.pdf |archive-url=https://web.archive.org/web/20200921072326/https://angeo.copernicus.org/articles/22/2973/2004/angeo-22-2973-2004.pdf |archive-date=2020-09-21 |url-status=live |access-date=9 November 2022 |language=en |doi-access=free }}</ref>

==See also==
* {{annotated link|Intergalactic space}}
* {{annotated link|Interplanetary space}}
* {{annotated link|Interstellar medium}}
* {{annotated link|Radio astronomy}}

== References ==
{{Reflist}}

{{Noise}}
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[[Category:Astronomical radio sources]]
[[Category:Noise]]