grrlscientist writes "How birds grow colored plumages, especially violet, blue and white.
From the story: Because blue light have very short wavelengths, it is reflected more easily than other colors of light with longer wavelengths. This was first understood in 1869, when scientist John Tyndall noted that miniscule particles in earth's atmosphere preferentially scattered blue light resulting in the familiar "sky blue" of a clear summer day. Shortly afterward, Rayleigh demonstrated that Tyndall's "fine particles" are actually gas molecules in Earth's atmosphere, specifically, nitrogen and oxygen. Tyndall's contribution is widely recognized by describing this phenomenon as "Tyndall scattering" and referring to structural blue colors as "Tyndall Blues.""
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