Rayleigh_sunset-ISS_Lalique-fish

Left: An image of a the setting sun photographed from the International Space Station [ISS015-E-10464, 3 June 2007, courtesy of NASA]. This illustrates the interplay between the direct and Rayleigh scattered light from the almost hidden Sun and the subsequent losses from the beam by absorption and scattering during its passage through different levels in the atmosphere. This process produces a sequence of colours that we call a 'Rayleigh spectrum'. The 'dirty' yellow band in the middle of the spectrum is produced by ozone absorption high in the atmospere. The ozone layer protects life at lower levels from dangerous ultraviolet radiation. This ring of light around the Earth is the source that illiminates the 'copper Moon' during a total Lunar eclipse.

Right: A similar palette of 'twilight' colours generated by shining a beam of white light through a glass fish (by Lalique, Paris: glass with a metal 'vapour' resulting in a perfect Rayleigh scatterer). The blue light scatters most strongly and is followed by the sequence of green-yellow, orange and red as the light penetrates deeper into the glass.

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