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Sky color

  1. Dec 18, 2012 #1
    I have a novice question.

    I know that the sky color is blue (at noon, when there is no clouds), because the air particles (mostly N2 and a little O2 ...and other) scatter short-wavelength light more than longer wavelengths.

    That is why we can't see the stars trought the atmosphere in daytime (the scattered light is with much more intensity then the light emmited from the brightest star).

    The question is why the stars can see us? All the pictures taken from above the atmosphere show the landscape of earth trought the atmosphere, where in the landscape is noon.
  2. jcsd
  3. Dec 18, 2012 #2


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    Staff: Mentor

    When viewed from say, the moon, the eart is much, much brighter than any star.
  4. Dec 18, 2012 #3
    So the reflected light from earth is brighter then the scattered light from atmosphere?
  5. Dec 18, 2012 #4
    Yes. Although when it comes to stars it is possible to view the brighter stars during the day even with just a amateur telescope due to how extended sources (the sky) and point sources (stars) behave with increased magnification.

    Note: If you don't know what you are doing never use a telescope while the sun is up...
  6. Dec 19, 2012 #5
    Compare Moon in daytime sky. It is clearly visible against blue sky - although not as bright as many objects on ground or in sky lit by the same sunlight.

    In clear sky, the disc of Sun is easily visible against blue sky, too. Since stars are inherently as hot as Sun, or slightly hotter or cooler, you should be able to magnify stars even in daytime sky to be almost as bright and distinctive, or even brighter and more distinctive, than Sun. Provided you are applying magnification starting hundreds of thousands of times, and apertures matching this (i. e. over a kilometre).
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