Why is the sky blue?
Sunlight is a mixture of colors, and the atmosphere scatters short-wavelength blue much more than long-wavelength red.
violetscatters most
bluewhat we see
green
yellow
orange
redscatters least
Sunlight is many colors mashed together
What we casually call ‘white’ light is really a stack of every visible wavelength. A prism (or a rainbow) just unstacks it back into a spectrum.
Air scatters small colors more
sun emits all colors
photons hit air molecules
blue scatters in every direction
we look up, blue everywhere
Air molecules are far smaller than the wavelength of visible light, which causes Rayleigh scattering, short-wavelength light bounces off them about ten times more than long-wavelength light.
Why sunsets are red
Near the horizon, sunlight slants through far more atmosphere. Most of the blue has already scattered away by the time the light reaches you, what’s left is the long, warm reds.