The sky appears blue because
- A. the atmosphere is blue in colour
- B. shorter wavelengths are scattered more strongly by air molecules
- C. the sea reflects onto the sky
- D. the Sun emits mostly blue light
Explanation
Rayleigh scattering varies as the inverse fourth power of wavelength, so blue is scattered far more than red and reaches the eye from all directions. At sunset the light travels a longer path through the atmosphere, so most of the blue is scattered away and the transmitted light appears red. The Sun's own output peaks in the green yellow region.
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