User:Milton Beychok/Sandbox: Difference between revisions

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==Why the daytime sky is usually blue==


[[Light]] is [[electromagnetic radiation]] that travels in waves of vibrating electric and [[magnetic field]]s and is a small part of a larger range of vibrating electromagnetic fields called the [[electromagnetic spectrum]]. Visible light is electromagnetic radiation visible to the human eye and is only a small part of the electromagnetic spectrum.
Light from the [[sun]] looks white, but is actually a combination of many [[color]]s. The colors blend continuously into one another. At one end of the spectrum are the red colors which have the highest [[wavelength]] and therefore  the lowest [[frequency]]. At the other end of the spectrum are the blues and violets with the lowest wavelengths and therefore the highest frequency.<ref name=BlueSky>[http://www.sciencemadesimple.com/sky_blue.html Why is the sky blue?]</ref><ref name=BlueSky2>[http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html Why is the sky blue?]</ref>
As light from the sun travels through Earth's atmosphere, it bumps into a bit of dust or a water droplet or a gas [[molecule]]. Dust particles and water droplets are very much larger than the wavelength of visible light. When light bumps into them, it gets reflected and bounced off in a different direction but the reflected light still appears white because it still contains all of the same colors it had before it was reflected.<ref name=BlueSky/><ref name=BlueSky2/>
However, gas molecules are much smaller than the wavelength of visible light. When light bumps into a gas molecule, it behaves differently than it does when it bumps into a dust particle or a water droplet in that some of the colors in the light are actually absorbed by the molecule. Subsequently, the molecule radiates or releases the light in a different direction. The colors in the radiated light are the same colors that were absorbed. The higher frequency colors (blues and violets) are absorbed more often than the lower frequency colors and this phenomena is called [[Rayleigh scattering]]. It was named after [[Lord Rayleigh]], an [[England|English]] physicist who first described it in the 1870's.<ref name=BlueSky/><ref name=BlueSky2/>
Thus, the lower frequency (higher wavelength) red, orange and yellow colors in the light from the sun mostly pass right through the atmosphere and are unaffected by the air. The higher frequency (lower wavelength) green, blue and violet colors in the light from the sun are absorbed by the gas molecules in the air and are then scattered all over the sky. That is why we see the daytime sky as being blue colored.<ref name=BlueSky/><ref name=BlueSky2/>

Revision as of 17:47, 11 March 2010

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