Why does the sky change color at sunset?

At sunset, sunlight has to pass through much more atmosphere before it reaches you. The shorter blue and violet wavelengths get scattered out of the direct beam, so the remaining light is richer in red, orange, and pink. Dust, pollution, and water droplets can intensify those colors by scattering and filtering the light further.

Clouds can also light up because they reflect and scatter the warm-colored sunlight. That’s why sunsets can look especially dramatic when the air has some haze or thin clouds.