human
I've always wondered: Why is the sky blue?
assistant
The sky is blue because of Rayleigh scattering. When sunlight reaches Earth’s atmosphere, it is scattered in all directions by molecules of air. This scattering causes some of the light to be shifted towards the red end of the spectrum, and the rest to be shifted towards the blue end of the spectrum. This effect is strongest at shorter wavelengths, so the blue end of the visible spectrum is scattered more than the other colors.