Radiation Damping; Light Scattering: Feynman's Physics Explained

Feynman Vol I8-9

An accelerating electron radiates light, and therefore radiates energy, so it must be losing energy — an effect that acts like a friction, or 'radiation damping,' on its motion. This is why an excited atom eventually stops glowing. Light scattering is just air molecules absorbing and re-radiating sunlight; blue light, with its higher frequency, scatters more strongly than red, which is why the sky is blue and sunsets are red.

The big idea

Atoms scatter blue light most — that's why the sky is blue.

Think about it

If air scatters blue light away in every direction, why does the setting Sun look red?

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