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Question about the Spectrum of Radiation Reaching the Earth

  1. Sep 11, 2011 #1
    Radiation with a wavelength in the visible light range is what mainly reaches the earth's surface.

    What is so special about visible light that makes it so easy to reach the surface compared to something like gamma rays with a smaller wavelength or something with a larger wavelength?

    Also, why does light near the 400nm range reach the earth in greater amounts than light near the 700nm range?
     
  2. jcsd
  3. Sep 11, 2011 #2

    phyzguy

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    Science Advisor

    The Earth's atmosphere absorbs most wavelengths of EM radiation before they reach the surface. There are certain 'windows' where the atmosphere is relatively transparent. These are mainly in the optical, the infrared,and the radio. This site has a nice plot of where the atmosphere is transparent:

    http://en.wikipedia.org/wiki/Optical_window

    As to why the Earth's atmosphere is transparent in this range, it is a relatively complex subject of how EM radiation interacts with matter, and what the Earth's atmosphere is made of. For example, X-rays and gamma rays are energetic enough to ionize the gas atoms in the atmosphere, so they lose energy as they ionize the gas atoms along their track until ultimately the energy is all absorbed. By contrast, long-wave infrared radiation is not energetic enough to ionize the gas atoms, but it can excite rotational and vibrational modes of the N2 and O2 gas molecules, and the energy is absorbed in this way.
     
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