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Light sky under primary rainbowwhy?

  1. Jun 30, 2012 #1
    Hello Forum,
    I understand how the primary rainbow is formed: dispersion by water droplets suspended in the air. A single internal reflection takes place. Red color (wavelength) emerges at about 42 degrees with respect to the observer....

    but why is the sky below the primary rainbow not showing dispersion? There are water droplets also below the rainbow....It is said that the rays emerger rather horizontally for those droplets...
    Perceiving white light means that emerging rays of different wavelengths are more or less overlapping each other..

  2. jcsd
  3. Jun 30, 2012 #2


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    The drops below the part where you see the rainbow reflect the light with this angle, too. They are visible as part of the rainbow for observers somewhere else.
  4. Jul 1, 2012 #3


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    From the title, you seem to be asking about the bright area below the rainbow. To a large extent it's not so much that this area is bright as that the area of the rainbow is dark. See http://en.wikipedia.org/wiki/Alexander's_band
  5. Jul 2, 2012 #4

    Andy Resnick

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    There is- recall that rainbows are an example of a caustic- constructive interference, if you like.

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