Editing Optical window

{{For|the optical element|Window (optics)}}
[[File:Atmospheric electromagnetic opacity.svg|thumb|301x301px|Rough plot of Earth's atmospheric [[transmittance]] (or opacity) to various wavelengths of electromagnetic radiation, including visible light.]]

The '''optical window''' is the portion of the [[optical spectrum]] that is {{em|not}} blocked by the [[Earth]]'s [[atmosphere]]. The window runs from around 300 [[nanometer]]s ([[Ultraviolet|ultraviolet-B]]) up into the range the [[human eye]] can detect, roughly 400–700 nm and continues up to approximately 2 [[Micrometre|μm]].<ref>{{Cite book|last=Dwivedi|first=Ravi Shankar|url=http://www.worldcat.org/oclc/959595730|title=Remote Sensing of Soils|publisher=Springer|year=2017|isbn=978-3-662-53740-4|pages=13|oclc=959595730|language=en}}</ref><ref>{{Cite book|last=Thorne|first=Anne P.|url=http://www.worldcat.org/oclc/906664124|title=Spectrophysics|publisher=Springer Science & Business Media|year=2012|isbn=978-94-009-1193-2|pages=3|oclc=906664124|language=en}}</ref> Sunlight mostly reaches the ground [[Rayleigh scattering|through]] the optical atmospheric window;<ref name=":1">{{Cite book|url=http://www.worldcat.org/oclc/4611045|title=Fluorocarbons, Environmental and Health Implications: Environmental Impact Statement|publisher=Food and Drug Administration|year=1978|pages=79|oclc=4611045|language=en}}</ref><ref>{{Cite book|last=Stergis|first=Christos G.|url=http://www.worldcat.org/oclc/1037802615|title=Rayleigh Scattering in the Upper Atmosphere|publisher=Air Force Cambridge Research Laboratories, Office of Aerospace Research, United States Air Force|year=1966|pages=273|oclc=1037802615|language=en}}</ref> the Sun is particularly active in most of this range (44% of the radiation emitted by the Sun falls within the visible spectrum and 49% falls within the infrared spectrum).<ref>{{Cite web|title=Climate Science Investigations South Florida - Energy: The Driver of Climate|url=http://www.ces.fau.edu/nasa/module-2/radiation-sun.php|access-date=2021-12-26|website=www.ces.fau.edu}}</ref>

==Definition==
The Earth's atmosphere is not totally transparent and is in fact 100% [[Opacity (optics)|opaque]] to many wavelengths (see plot of Earth's opacity); the wavelength ranges to which it is transparent are called [[Atmospheric window|atmospheric windows]].<ref>{{Cite web|last=|first=|title=The Atmospheric Window {{!}} US Department of Commerce, NOAA|url=https://www.weather.gov/jetstream/absorb|access-date=2021-12-26|website=www.weather.gov|language=EN-US}}</ref>  

=== Disambiguation of the term 'optical spectrum' ===
Although the word ''optical'', deriving from [[Ancient Greek]] ὀπτῐκός (optikós, "of or for sight"), generally refers to something visible or visual,<ref>{{Cite web|title=Definition of OPTICAL|url=https://www.merriam-webster.com/dictionary/optical|access-date=2021-12-27|website=www.merriam-webster.com|language=en}}</ref> the term ''optical spectrum'' is used to describe the sum of the [[Visible spectrum|visible]], the [[ultraviolet]] and the [[infrared]] spectra (at least in this context).<ref>{{Cite book|last1=Pedrotti|first1=Frank L.|url=http://www.worldcat.org/oclc/1029320342|title=Introduction to optics|last2=Pedrotti|first2=Leno Matthew|last3=Pedrotti|first3=Leno S.|date=2018|publisher=[[Cambridge University Press]]|isbn=978-1-108-42826-2|pages=7–8|language=English|oclc=1029320342}}</ref><ref>{{Cite book|last=Mazda|first=F. F.|url=http://www.worldcat.org/oclc/1100870227|title=Electronics Engineer's Reference Book|publisher=Butterworth-Heinemann|year=2013|isbn=978-1-4831-6106-8|pages=9/3|oclc=1100870227|language=en}}</ref> 

=== Optical atmospheric window ===
[[File:Solar_spectrum_en.svg|thumb|301x301px|Solar [[irradiance]] spectrum above atmosphere and at surface. Extreme UV and [[X-ray|X-rays]] are produced (at left of wavelength range shown) but comprise very small amounts of the Sun's total output power.]]
The optical atmospheric window is the optical portion of the [[electromagnetic spectrum]] that passes through the Earth's atmosphere, excluding its infrared part;<ref>{{Cite book|last=Kartalopoulos|first=Stamatios V.|url=http://www.worldcat.org/oclc/773844977|title=Free space optical networks for ultra-broad band services|publisher=Wiley-Blackwell/IEEE|year=2011|isbn=978-0-470-64775-2|location=Oxford|pages=33|language=English|oclc=773844977}}</ref> although, as mentioned before, the optical spectrum also includes the IR spectrum and thus the optical window could include the [[infrared window]] (8 – 14 μm), the latter is considered separate by convention, since the visible spectrum is not contained in it.<ref>{{Cite book|last=United States Congress {{!}} Committee on Science and Astronautics|url=http://www.worldcat.org/oclc/968587432|title=1970 NASA Authorization. hearings before the United States House Committee on Science and Astronautics, Ninety-First Congress, first session, on Mar. 4, 5, 1969. Part 1|publisher=U.S. G.P.O.|year=1973|location=Washington|pages=981|language=English|oclc=968587432}}</ref>

== Historical importance for observational astronomy ==
Up until the 1940s, astronomers could only use the visible and near infrared portions of the optical spectrum for their observations. The first great astronomical discoveries such as the ones made by the famous [[Italian language|Italian]] [[polymath]] [[Galileo Galilei]] were made using [[Optical telescope|optical telescopes]] that received light reaching the ground through the optical window.<ref>{{Cite book|last=Drake|first=Stillman|url=http://archive.org/details/galileoatwork00stil|title=Galileo at work : his scientific biography|publisher=Chicago : University of Chicago Press|others=Internet Archive|year=1978|isbn=978-0-226-16226-3|pages=146|language=English}}</ref> After the 1940s, the development of radio telescopes gave rise to the even more successful field of [[radio astronomy]] that utilized the [[radio window]].<ref>{{Cite book|last=Wilson |first=Thomas |url=http://worldcat.org/oclc/954868912|title=Tools of Radio Astronomy |publisher=[[Springer Science+Business Media |Springer-Verlag GmbH]]|year=2016|isbn=978-3-662-51732-1|pages=1–2|oclc=954868912}}</ref> 

==See also==
*[[Infrared window|Infrared (atmospheric) window]]
*[[Optical window in biological tissue]]
*[[Radio window]]

==References==
{{Reflist}}

{{DEFAULTSORT:Optical Window}}
[[Category:Electromagnetic spectrum]]
[[Category:Observational astronomy]]