• Question: why is the sky blue?

    Asked by SAYr9 to Ellen, Elliot, Hazel, Rupesh, Thomas on 11 Jun 2016.
    • Photo: Elliot Jokl

      Elliot Jokl answered on 11 Jun 2016:

      Hello and thanks for the question!

      If you shine a light through a prism, it splits up into the different colours of the rainbow. This is because the light bends (refracts) differently depending on the wavelength of the light. So red light, which has longer wavelengths, bends less than blue light, which has shorter wavelengths.

      A similar kind of thing happens in our atmosphere when the sunlight passes through it – the blue light is scattered around more than the shorter wavelengths of light and so this is what we see. This was discovered by a man called Lord Rayleigh in the 1800’s.

      Now, there is something missing in this answer, but I want you to have a little think about what that is and try and ask me a follow up question about it. As a clue, maybe you want to think about what other colours there are in the rainbow. If you get stuck, just let us know and I’m sure someone will finish off the answer.

    • Photo: Thomas Biggans

      Thomas Biggans answered on 11 Jun 2016:

      The colour of something is the wavelength of light that comes off the object and into your eye. Sometimes it’s easier to think of wavelengths in terms of energy which is a way to measure how excited light is, short wavelength high energy very excited, long wavelength low energy not excited.

      Blue is a short wavelength so it’s a very excited bit of light. When light enters the atmosphere from the sun it collides with oxygen and nitrogen in the air, the less excited colours of light are pushed over a little bit and continue on in the general direction they were travelling but the more excited colours bounce off the oxygen and nitrogen in all different directions. So when you look at the sky you see blue from every direction.

    • Photo: Hazel Garvie-Cook

      Hazel Garvie-Cook answered on 16 Jun 2016:

      The light from the sun is made up of lots of different colours, which combine to make it look white. The molecules in air scatter blue light more than they do any other colours, so we see a blue sky. When the sun is lower in the sky, at sunset, the light has more air to travel through. More blue light is scattered by the air molecules, so we’re left with more yellow and red light which is why we see nice red sunsets.

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