PhysicsThe Human Eye and the Colourful World

Tyndall & Sky Colour

Rayleigh scattering ∝ 1/λ⁴ explains the blue sky and red sunset.

Wavelength450 nm

Air path length1 ×

Relative scattering

5.86× red

Perceived sky

Blue (noon)

Scattering5.86

Scattering of light (Tyndall effect)Relative scattering: 5.86 × red

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Blue light scatters ~5.5× more than red, so the sky looks blue overhead and red at sunset.

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