Have you ever wondered why the sky is blue? The sunlit sky is blue because air scatters short-wavelength light more than longer wavelengths. Since blue light is at the short-wavelength end of the visible spectrum, it is more strongly scattered in the atmosphere than long-wavelength red light. The result is that when looking toward parts of the sky other than the sun, the human eye perceives them to be blue. The color perceived is similar to that obtained by a monochromatic blue of a wavelength of 474–476 nm mixed with white light, i.e., an unsaturated blue light. The explanation of the blue color by Rayleigh in 1871 is one of the most famous examples of the application of dimensional analysis in solving a problem in physics.