View source for Astronomy:Cosmic background radiation

{{Short description|Electromagnetic radiation from the Big Bang}}
{{Physical cosmology}}
[[Image:Cobe-cosmic-background-radiation.gif|thumb|256px|Temperature of the cosmic background radiation spectrum based on [[Astronomy:Cosmic Background Explorer|COBE]] data: uncorrected (top); corrected for the dipole term due to our peculiar velocity (middle); corrected additionally for contributions from our galaxy (bottom).]]

'''Cosmic background radiation''' is [[Physics:Electromagnetic radiation|electromagnetic radiation]] that fills all space. The origin of this radiation depends on the region of the [[Physics:Electromagnetic spectrum|spectrum]] that is observed. One component is the [[Astronomy:Cosmic microwave background|cosmic microwave background]]. This component is redshifted [[Physics:Photon|photon]]s that have freely streamed from an [[Astronomy:Recombination (cosmology)|epoch when the Universe became transparent]] for the first time to radiation. Its discovery and detailed observations of its properties are considered one of the major confirmations of the [[Astronomy:Big Bang|Big Bang]]. The discovery (by chance in 1965) of the cosmic background radiation suggests that the early universe was dominated by a radiation field, a field of extremely high temperature and pressure.<ref>{{cite news|url=http://whatisusa.info/the-first-minutes-of-the-big-bang/|title=First minutes of the Big Bang|publisher=What is USA News|date=12 March 2014|access-date=2013-11-19|archive-url=https://web.archive.org/web/20140312121214/http://whatisusa.info/the-first-minutes-of-the-big-bang/|archive-date=12 March 2014|url-status=dead}}</ref>

The [[Astronomy:Sunyaev–Zel'dovich effect|Sunyaev–Zel'dovich effect]] shows the phenomena of radiant cosmic background radiation interacting with "[[Physics:Electron|electron]]" clouds distorting the spectrum of the radiation.

There is also background radiation in the [[Physics:Infrared|infrared]], [[Physics:X-ray|x-ray]]s, etc., with different causes, and they can sometimes be resolved into an individual source. See [[Astronomy:Cosmic infrared background|cosmic infrared background]] and [[Astronomy:X-ray background|X-ray background]]. See also [[Astronomy:Cosmic neutrino background|cosmic neutrino background]] and [[Astronomy:Extragalactic background light|extragalactic background light]].

==Timeline of significant events==

1896: 
[[Biography:Charles Édouard Guillaume|Charles Édouard Guillaume]] estimates the "radiation of the stars" to be 5.6&nbsp;[[Kelvin|K]].<ref name="history">{{cite journal|url=http://redshift.vif.com/JournalFiles/Pre2001/V02NO3PDF/V02N3ASS.PDF|title=History of the 2.7 K Temperature Prior to Penzias and Wilson|first1=A. K. T.|last1=Assis|first2=M. C. D.|last2=Neves|journal=Apeiron|volume=2|number=3|date=3 July 1995}}</ref>

1926: 
Sir [[Biography:Arthur Eddington|Arthur Eddington]] estimates the non-thermal radiation of [[Astronomy:Starlight|starlight]] in the galaxy has an effective temperature of 3.2&nbsp;K. [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1927Sci....66...81E&amp;db_key=AST&amp;data_type=HTML&amp;format=&amp;high=42ca922c9c22437]

1930s:
[[Biography:Erich Regener|Erich Regener]] calculates that the non-thermal spectrum of cosmic rays in the galaxy has an effective temperature of 2.8&nbsp;K.<ref name="history"/>

1931:
The term ''microwave'' first appears in print: "When trials with wavelengths as low as 18&nbsp;cm were made known, there was undisguised surprise that the problem of the micro-wave had been solved so soon." ''Telegraph & Telephone Journal'' XVII. 179/1"

1938:
[[Biography:Walther Nernst|Walther Nernst]] re-estimates the cosmic ray temperature as 0.75&nbsp;K.<ref name="history"/>

1946:
The term "[[Physics:Microwave|microwave]]" is first used in print in an astronomical context in an article "Microwave Radiation from the Sun and Moon" by Robert Dicke and Robert Beringer.

1946:
Robert Dicke predicts a microwave background radiation temperature of 20&nbsp;K (ref: Helge Kragh)

1946:
Robert Dicke predicts a microwave background radiation temperature of "less than 20&nbsp;K" but later revised to 45&nbsp;K (ref: Stephen G. Brush).

1946:
[[Biography:George Gamow|George Gamow]] estimates a temperature of 50&nbsp;K.<ref name="history"/>

1948:
Ralph Alpher and [[Biography:Robert Herman|Robert Herman]] re-estimate Gamow's estimate at 5&nbsp;K.<ref name="history"/>

1949:
Ralph Alpher and Robert Herman re-re-estimate Gamow's estimate at 28&nbsp;K.

1960s:
Robert Dicke re-estimates a MBR (microwave background radiation) temperature of 40&nbsp;K (ref: Helge Kragh).

1965:
Arno Penzias and [[Biography:Robert Woodrow Wilson|Robert Woodrow Wilson]] measure the temperature to be approximately 3&nbsp;K. Robert Dicke, P. J. E. Peebles, P. G. Roll and [[Biography:David Todd Wilkinson|D. T. Wilkinson]] interpret this radiation as a signature of the Big Bang.<ref name="history"/>

==See also==
* [[Astronomy:Hot dark matter|Hot dark matter]]
* [[Biology:Irradiation|Irradiation]]
* [[Physics:Unruh effect|Unruh effect]]

==References==
{{reflist}}

==External links==
*[https://web.archive.org/web/20111017181402/http://heasarc.nasa.gov/docs/objects/background/background.html The Diffuse X-ray and Gamma-ray Background & Deep Fields]

[[Category:Cosmic background radiation| ]]
[[Category:Observational astronomy]]
[[Category:Physical cosmology]]
[[Category:Electromagnetic radiation]]

{{Sourceattribution|Cosmic background radiation}}