Why does the Sun look orange at sunrise and sunset?

When the Sun is near the horizon, its light passes through up to 30 times more atmosphere than when it is overhead. Air molecules scatter shorter wavelengths, especially blue and violet, in all directions through Rayleigh scattering. The more air the light passes through, the more blue is removed, so the remaining light that reaches the viewer is dominated by reds and oranges. Dust, pollution and volcanic ash in the atmosphere can scatter even more light, producing deeper reds. High, thin clouds can catch this orange light and glow vividly, creating dramatic sunrise and sunset skies.