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 Spanish - Chinese The Optics Book - Scattering&Spectrum Written by:Karen
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In this section:

The Optics Book

Spectrum
Scattering
Green water
Fog Lights
8. Color
9. Interferences & difraction
10. Polarization
11. Quantic Optics

Scattering

Did you ever wonder why the sky was blue?

In 1971, the English scientist, Lord Rayleigh explained the scattering of Light.  The scattering of particles smaller than a wavelength is now also referred to as Rayleigh scattering.

The air is filled with thousands of molecules of nitrogen and oxygen.  These molecules are spread out randomly.  Photons of Light can set these molecules into an oscillation.  When this happens, the molecules will absorb and emit photons.  The emitted photons are scattered in a random manner because of the random placement of the molecules themselves.

Light, which is closer to the ultraviolet part of the electromagnetic spectrum, will scatter more widely than Light that is closer to the infrared part of the electromagnetic spectrum.  This is because the molecules of nitrogen and oxygen have natural frequencies that are in the ultraviolet zone.  The closer a frequency gets to the natural frequency of the object, the larger the amplitude of the oscillation will be.  As the frequency of the Light approaches that of the UV frequency (this would mean the colors like blue and violet), the amplitude of the oscillation would be larger, and the photons would be scattered more widely.

The sky therefore appears to be blue because when the white Light of the sun is scattered, the blue color is scattered the most.  It does not appear to be violet, although violet would scatter the most, because there is not much violet in the sunLight.  The red side of the spectrum can travel through the atmosphere farther because it does not scatter as much.  But, the sky is not always blue.  For instance, during sunrise and sunset, the sky appears to be reddish.  This is because the rays from the sun approach the earth at closer angles to the atmosphere, and have more molecules to penetrate through.  The blue Light is scattered very far about, and the red and orange Lights are the only ones that are able to get through the atmosphere.