• Question: why is the sky blue

    Asked by 758furk43 to Chris, Joanne, Kathryn, Kieran, Sarah on 7 Nov 2017. This question was also asked by 895furk43, beckyđź’—.
    • Photo: Kieran Fraser

      Kieran Fraser answered on 7 Nov 2017:

      That’s an interesting question – this page has an excellent explanation (with awesome pictures!): https://spaceplace.nasa.gov/blue-sky/en/

      My understanding is: the sun shines out all the colours of the rainbow (even though it looks white to us) in the form of waves – some of the waves are ‘choppier’ than others (like a rough sea, the waves are close together). Blue is one of the choppier light waves. The red light wave is less ‘choppy’ like a calm sea, so nearer to flat. So sunlight beams down on us and, when it reaches the atmosphere, it hits lots of tiny air molecules and scatters in all directions. Blue light scatters most because it is the choppiest wave. So we see the sky as mostly this scattered blue light. The further away we look in the sky, the lighter the blue colour gets too – like it fades to white. This is due to the blue light having to travel through even more air, so it hits even more air molecules and scatters again and again.

    • Photo: Chris Werner

      Chris Werner answered on 8 Nov 2017:

      I love this question, so thanks for asking it, and believe me when I saw that it puzzled scientists for quite a long time! Have you done the experiment when you shine light onto a prism and it splits into different colours? If you haven’t get your teacher to show you. One of these colours is blue. The different colours have different wavelengths, and blue has a shorter wavelength than red. Sunlight reaches Earth’s atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth’s atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves.

      Then during sunrise and sunset, when the sky is redder, its light is passing through more of the atmosphere to reach you. Even more of the blue light is scattered, allowing the reds and yellows to come through

      Its also worth pointing out that the three different types of colour receptors in the retina of the human eye respond most strongly to red, green and blue wavelengths, giving us our colour vision.

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