Some sunsets exhibit a phenomenon called "green flash," where there is a quick flash of green light right as the sun is setting. I have seen this myself several times, and sort of understand it. I am a bit frustrated at my inability to explain it better to my family.

I understand how Rayleigh scattering would make the dominant color shift towards the blue just after the sun passes below the horizon. How does mirage cause the green light to refract more than the blue? Is there an easy way to use the two effects to estimate the wavelength of the flash?


Refraction causes the shift to shorter wavelength, but scattering causes the shortest wavelengths to usually not be observed, as explained by astronomer Andrew Young here.

In rare instances the flash can be blue, as seen in these photographs at Atmospheric Optics.

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    $\begingroup$ maybe you should expand a bit using the explanation in your first link. It seems that the color sequence dispersion of the images of the sun always leaves the image of the sun in the largest wavelengths disappear first. "at sunset, the refractive delay of the sunset is usually a second or two longer for blue and violet " Inversion layers create mirages that magnify this effect." $\endgroup$ – anna v Mar 10 '14 at 4:53

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