Editing Green flash (section)

==Explanation==

Green flash occurs because the [[atmosphere]] causes the light from the Sun to [[dispersion (optics)|separate]], or [[refract]], into different frequencies. Green flashes are enhanced by [[Mirage of astronomical objects|mirages]], which increase [[refraction]]. A green flash is more likely to be seen in stable, clear air, when more of the light from the setting sun reaches the observer without being scattered. One might expect to see a blue flash, since blue light is refracted most of all and the blue component of the sun's light is therefore the last to disappear below the horizon, but the blue is preferentially [[Rayleigh scattering|scattered out of the line of sight]], and the remaining light ends up appearing green.<ref name="Explaining Green Flashes">{{cite web |url=http://mintaka.sdsu.edu/GF/explain/explain.html |title=Explaining Green Flashes |author=Andy Young |website=mintaka.sdsu.edu}}</ref>

With slight [[magnification]], a green rim on the top of the [[sun|solar disk]] may be seen on most clear-day sunsets, although the flash or ray effects require a stronger layering of the atmosphere and a mirage, which serves to magnify the green from a fraction of a second to a couple of seconds.<ref name="Explaining Green Flashes"/>

While simple atmospheric refraction or lensing explains the background gradient of red-amber twilight, the primary potential cause of the bright, verdant discontinuity from that gradient known as the Green Flash may be due to naturally-occurring coherent (laser) light. Part of this phenomenon was recently discovered by researchers at the [[Washington University School of Medicine]], regarding infrared-laser light converting-up (or upconverting) to visible-green laser light, causing what researchers there call "a double hit" of photons on the retina, creating the perception of bright neon green from an originally invisible infrared laser.<ref name="The human eye can see ‘invisible’ infrared light">{{cite web |url=https://source.wustl.edu/2014/12/the-human-eye-can-see-invisible-infrared-light/ |title=The human eye can see 'invisible' infrared light |website=source.wustl.edu |author=Jim Dryden |date=December 1, 2014 |access-date=2025-01-25}}</ref> 

Doubling the wavelength of green light yields roughly 1000-1100 nm infrared light, so the most likely hypothesis is that the Green Flash is coherent upconverted infrared (laser) light that "double-hits" the retina or camera lens, creating the effect of bright green (additionally, this explains why the Green Flash is also sometimes blue or purple; coherent infrared light can upconvert to any color of visible light if the conditions are met).