As light moves through the atmosphere, it continues to go straight until it bumps into a bit of dust or a gas molecule. Then what happens to the light depends on its wave length and the size of the thing it hits. Dust particles and water droplets are much larger than the wavelength of visible light. When light hits these large particles, it gets reflected, or bounced off, in different directions.
The different colors of light are all reflected by the particle in the same way. The reflected light appears white because it still contains all of the same colors. Gas molecules are smaller than the wavelength of visible light. If light bumps into them, it acts differently.
When light hits a gas molecule, some of it may get absorbed. After awhile, the molecule radiates releases, or gives off the light in a different direction.
The color that is radiated is the same color that was absorbed. The different colors of light are affected differently. All of the colors can be absorbed. But the higher frequencies blues are absorbed more often than the lower frequencies reds. This process is called Rayleigh scattering. It is named after Lord John Rayleigh, an English physicist, who first described it in the 's.
The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through.
Little of the red, orange and yellow light is affected by the air. However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions.
It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue. As you look closer to the horizon, the sky appears much paler in color. To reach you, the scattered blue light must pass through more air. When we look at an arbitrary point in the sky, away from the sun, we see only the light that was redirected by the atmosphere into our line of sight.
Because that occurs much more often for blue light than for red, the sky appears blue. Violet light is actually scattered even a bit more strongly than blue. More of the sunlight entering the atmosphere is blue than violet, however, and our eyes are somewhat more sensitive to blue light than to violet light, so the sky appears blue.
When we view the setting sun on the horizon, the opposite occurs. We see only the light that has not been scattered into other directions. The red wavelengths of sunlight that pass through the atmosphere without being scattered much reach our eyes, while the strongly scattered blue light does not. The longer distance that the sunlight travels through the atmosphere when it is on the horizon amplifies the effect--there are more opportunities for blue light to be scattered than when the sun is overhead.
Thus, the setting sun appears reddish. In a polluted sky, small aerosol particles of sulfate, organic carbon, or mineral dust further amplify the scattering of blue light, making sunsets in polluted conditions sometimes spectacular. Clouds, on the other hand, are made of water droplets that are much larger than the wavelengths of visible light.
The way they scatter sunlight is determined by how the light is refracted and internally reflected by, and diffracted around, the cloud droplets. For these particles the difference between the scattering of blue and red light is not nearly so large as it is for gas molecules. Hence, our eyes receive substantial scattered light at all visible wavelengths, causing clouds to appear more white than blue, especially when viewed against a blue sky background.
General Science. AdaMcVean Leave a comment! Is it true that the Beatles wrote a song about LSD? Is it true that you cannot eat polar bear liver? What is Guarana? Are You Left-Handed? Facebook Twitter YouTube Instagram. Accessibility Log in.
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