The sky appears blue to us because of the way Earth's atmosphere scatters sunlight. When sunlight reaches Earth's atmosphere, it is made of a spectrum of colors, with shorter wavelengths like blue and violet being scattered more easily than longer wavelengths like red and yellow. As sunlight moves through the atmosphere, the shorter blue wavelengths are scattered in all directions by the gases and particles in the air. This scattering causes the blue light to spread across the sky, making it appear blue to our eyes.
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