= Why the sky is blue
In a clear <terrestrial atmosphere>, <Rayleigh scattering> by air <molecules> redirects some sunlight toward an observer looking away from the <Sun>. Shorter <wavelengths> are preferentially scattered, enriching the scattered <light> in blue compared with the incoming sunlight. Along the longer atmospheric path to the low <Sun>, more short-<wavelength> <light> is removed from the direct beam, helping produce red sunsets. https://spaceplace.nasa.gov/blue-sky/en/[NASA Space Place, Why Is the Sky Blue?: scattered sunlight and red sunsets]{ref}.
Violet <light> has an even shorter <wavelength> than blue <light>, so the <Rayleigh scattering wavelength dependence> alone cannot predict the perceived sky color. The incoming solar <optical spectrum> and the eye's differing response to <wavelengths> both matter; human vision is less sensitive to violet than to blue. https://www.weather.gov/fgz/SkyBlue[NOAA National Weather Service, Why Is The Sky Blue?: solar spectrum and visual response]{ref}. <Multiple scattering> and other atmospheric particles also affect the observed sky. Cloud droplets are generally too large for this simple <Rayleigh scattering> model: <Mie scattering> describes spherical droplets, with much weaker visible <wavelength> selectivity, while repeated scattering helps make clouds appear white. https://www.giss.nasa.gov/edu/icp/research/ppa/1997/reyes/[NASA GISS, Aerosols in the Atmosphere: particle size, Mie scattering and white clouds]{ref}.
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