• Question: Why is the sky blue?

    Asked by giuola to Meeks, Pete, Stephen, Steve, Tom on 22 Jun 2010 in Categories: . This question was also asked by isabella.
    • Photo: Marieke Navin

      Marieke Navin answered on 21 Jun 2010:

      Hey Giuola and Isabella – scattering! (it’s called Rayleigh scattering). Sunlight is scattered off molecules of air and this effects the short wavelength (blue) light the most. As you look to the horizon the sky looks less blue and more white because even more of the light is being scattered as it has more air to go through.

      There is one other reason as well that my chemistry teacher at school told me. Oxygen isn’t a clear gas, but blue and you are also looking through a lot of oxygen when you look at the sky.

    • Photo: Stephen Curry

      Stephen Curry answered on 21 Jun 2010:

      The sky is blue because the molecules in the air in the upper atmosphere scatter the sunlight that passes through it.

      That means that the light bounces off in all directions. But the efficiency with which light is scattered depends on the wavelength of the light. Shorter wavelengths, at the blue end of the spectrum, are scattered more efficiently than red light. So the blue light predominates the colours that we see in the sky.

    • Photo: Steve Roser

      Steve Roser answered on 22 Jun 2010:

      The colour of the sky comes from scattered light from the sun – that is light that is being bounced off something – the something in this case is atoms in the atmosphere. It turns out that light of shorter wavelength (the blue end) is scattered more than teh long wavelength (the red end) (this is called Rayleighs Law) so we see more blue scattered light. At dusk, light from the sun passes thru a thicker layer of air, so more light is scattered, and all that is left is red – hence we get red sky at night coming straight from the sun.

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