• Question: Why is the sky blue?

    Asked by 10bisbenh to Christina, Colin, Jess, Samaneh, Steve on 24 Jun 2013.
    • Photo: Steven Gardner

      Steven Gardner answered on 24 Jun 2013:

      The sky is blue because of an effect called Rayleigh scattering. The light from the sun hits particles in the atmosphere and is scattered in all directions, some of which ends up being picked up by your eyes. The probability of Rayleigh scattering happening is dependent on the wavelength of the light coming in, basically blue light is more likely to be scattered than red so you see the sky as blue.

      If there were no atmosphere, the sky would be black, because there would be nothing for the light to scatter from, so none of it would reach your eyes.

Comments

  • Photo: spacenut1982

    spacenut1982 commented on :

    What makes say blue more likely to be scattered??

    • Photo: Steve

      Steve commented on :

      rayleigh scattering is strongly wavelength dependent. In mathematical terms, the scattering intensity is inversely proportional to the fourth power of the wavelength. So shorter wavelengths scatter much more.

      The next question you might ask is, “well then why isn’t the sky violet?”, and the answer is that the sun doesn’t actually produce very much violet light. The peak of the sun’s spectrum is in the visible range (which is why we’ve evolved eyes to see it!).