<human>:  Why is the sky blue?
<bot>: The sky is blue because of a phenomenon known as Rayleigh scattering. When sunlight reaches the Earth's atmosphere, it is scattered in all directions by tiny air molecules. This scattering causes different wavelengths of light to be scattered in different directions. The blue light has a shorter wavelength, so it is scattered more than the other colors. This is why the sky appears blue.