• Question: Why is the sky blue?

    Asked by Kate and Peckasso :) to Chris, Josh, Rebecca, Rob, Susan on 22 Jun 2015.
    • Photo: Rebecca Dewey

      Rebecca Dewey answered on 22 Jun 2015:

      The atmosphere consists of lots of molecules (particularly air and water vapour). Because these molecules are quite small, they scatter the light at shorter wavelengths (i.e. blue, purple light) more than long wavelengths (red). So out of the white light that reaches us from the sun, the blue light is reflected around everywhere and the sky looks blue.

    • Photo: Susan Cartwright

      Susan Cartwright answered on 22 Jun 2015:

      (This question has been asked and answered many times already!)

      The atmosphere contains small particles: air molecules, tiny water droplets, fine dust. These scatter light by a process called Rayleigh scattering, in which shorter wavelengths (purple, blue) get scattered a lot more than longer wavelengths (yellow, red). Hence, by the time it reaches the ground, the blue light has been bounced around so many times its original direction has been totally lost – so, wherever you look in the sky, you see blue light. Yellow and red, in contrast, are scattered much less, so are still coming from the direction of the Sun.

      At sunrise or sunset, the light is coming through a much greater thickness of atmosphere, and other colours are also scattered. This is why the Sun at sunrise or sunset looks red instead of yellow, and the sky around it is typically orange or orange-yellow.

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