Editing Rayleigh scattering (section)

== Cause of the blue color of the sky==
{{Main|Diffuse sky radiation}}

[[File:CircularPolarizer.jpg|thumb|right|Scattered blue light is [[Polarization (waves)|polarized]]. The picture on the right is shot through a [[Polarizing filter (photography)|polarizing filter]]: the [[polarizer]] transmits light that is [[Linear polarization|linearly polarized]] in a specific direction.]]
The blue color of the sky is a consequence of three factors:<ref name=SmithAJP2005>{{Cite journal |last=Smith |first=Glenn S. |date=2005-07-01 |title=Human color vision and the unsaturated blue color of the daytime sky |url=https://pubs.aip.org/ajp/article/73/7/590/1056162/Human-color-vision-and-the-unsaturated-blue-color |journal=American Journal of Physics |language=en |volume=73 |issue=7 |pages=590–597 |doi=10.1119/1.1858479 |bibcode=2005AmJPh..73..590S |issn=0002-9505}}</ref> 
*the [[blackbody radiation | blackbody]] spectrum of [[sunlight]] coming into the Earth's atmosphere, 
*Rayleigh scattering of that light off oxygen and nitrogen molecules, and 
*the response of the human visual system.

The strong wavelength dependence of the Rayleigh scattering (~''λ''<sup>−4</sup>) means that shorter ([[blue]]) wavelengths are scattered more strongly than longer ([[red]]) wavelengths. This results in the indirect blue and violet light coming from all regions of the sky. The human eye responds to this wavelength combination as if it were a combination of blue and white light.<ref name=SmithAJP2005/>

Some of the scattering can also be from sulfate particles. For years after large [[Plinian eruption]]s, the blue cast of the sky is notably brightened by the persistent sulfate load of the [[stratospheric]] gases. Some works of the artist [[J. M. W. Turner]] may owe their vivid red colours to the eruption of [[Mount Tambora]] in his lifetime.<ref name="zerefos">{{Citation
 | last1 = Zerefos | first1 = C. S.
 | last2 = Gerogiannis | first2 = V. T.
 | last3 = Balis | first3 = D.
 | last4 = Zerefos | first4 = S. C.
 | last5 = Kazantzidis | first5 = A.
 | title = Atmospheric effects of volcanic eruptions as seen by famous artists and depicted in their paintings
 | journal= Atmospheric Chemistry and Physics
 | volume = 7
 | number = 15
 | date = 2007 
 | pages = 4027–4042
 | doi = 10.5194/acp-7-4027-2007 | bibcode = 2007ACP.....7.4027Z
 |url=http://hal.archives-ouvertes.fr/docs/00/30/27/17/PDF/acpd-7-5145-2007.pdf
 | doi-access = free
 }}</ref>

In locations with little [[light pollution]], the moonlit night sky is also blue, because moonlight is reflected sunlight, with a slightly lower [[color temperature]] due to the brownish color of the Moon. The moonlit sky is not perceived as blue, however, because at low light levels human vision comes mainly from [[rod cells]] that do not produce any color perception ([[Purkinje effect]]).<ref>{{Citation |last=Choudhury |first=Asim Kumar Roy |title=Unusual visual phenomena and colour blindness |date=2014 |url=https://linkinghub.elsevier.com/retrieve/pii/B978085709229850005X |work=Principles of Colour and Appearance Measurement |pages=185–220 |publisher=Elsevier |language=en |doi=10.1533/9780857099242.185 |isbn=978-0-85709-229-8 |access-date=2022-03-29}}</ref>