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Atmospheric light scattering: Difference between revisions
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Mie scattering in contrast occurs for much larger particles (water droplets for instance). In this limit, the scattering is of equal strength for all wavelength (i.e. pure Mie-scattered light is white), but the scattering is strongly directional - the scattered light prefers to go close to its original direction. Mie scattering thus tends to create bright white halos around light sources. | Mie scattering in contrast occurs for much larger particles (water droplets for instance). In this limit, the scattering is of equal strength for all wavelength (i.e. pure Mie-scattered light is white), but the scattering is strongly directional - the scattered light prefers to go close to its original direction. Mie scattering thus tends to create bright white halos around light sources. | ||
As long as the light scattering effect is weak, a medium is called optically thin. The relevant measure is the ratio of the light attenuation length divided by the size of the medium which must be smaller than one, and the defining characteristic of an optically thin medium is that you can look through. This is certainly true for the upper atmosphere where visibility ranges are easily several hundred kilometers whereas the thickest part of the atmosphere is just about 30 km vertical size. Thus, a dark blue sky is actually the blackness of space, seen through the light blue-white glow of Rayleigh scattering. | |||
As clouds demonstrate quite drastically, water droplets can easily make the atmosphere optically thick. | |||
== Atmospheric haze == | == Atmospheric haze == | ||