Science & history · The Sun and Earth's sky
Why the sky is blue and sunsets are red
Sunlight is scattered by the gases and particles in the atmosphere, and blue light is scattered most.
Blue overhead
Blue light travels as shorter, smaller waves and is scattered more than red, so blue light reaches you from every part of the sky.
Red at the horizon
When the Sun is low, its light passes through much more of the atmosphere to reach you. Even more blue is scattered out of the beam, and the reds and yellows are what get through. Dust and haze can deepen the colours.
Sources
- NASA Space Place Why Is the Sky Blue? (opens in a new tab) for scattering of shorter wavelengths; redder low Sun · checked 2 October 2026