Why the Sky Is Blue: Scattering of Sunlight

The sky looks blue because sunlight scatters off air molecules in Earth’s atmosphere.
This effect is called Rayleigh scattering, which favors shorter wavelengths like blue and violet.
Our eyes are more sensitive to blue than violet, so the sky appears blue instead of purple.
At sunrise and sunset, sunlight travels through more atmosphere, scattering blue away and leaving reds and oranges.
Scattering works best when particles are much smaller than the wavelength of light.
The Moon’s daytime sky looks black because it has no atmosphere to scatter sunlight.
Pollution and dust can shift sky colors, sometimes making them whitish or hazy.
The deep blue of high-altitude skies comes from thinner air scattering less overall light.
Astronauts orbiting Earth see a thin blue halo around the planet—our scattering atmosphere.
Without scattering, the daytime sky would look as black as outer space.