• Question: Bonjour! Why is the sky blue? Why are the grass and trees green? Thanks

    Asked by fjaafar to Arttu, Ceri, James_M, Monica, Philip on 20 Jun 2011. This question was also asked by sgill, vampiregirl.
    • Photo: Arttu Rajantie

      Arttu Rajantie answered on 20 Jun 2011:

      The sky is blue because shorter wavelength (blue light) scatters more off particles in the atmosphere. The longer wavelength scatter less and therefore they are still travelling in the same direction when the reach us, but blue light seems to be coming from all directions.

      Grass and trees are green because chlorophyll, which they use for photosynthesis, is green. In principle black would be better because it would absorb more light, but I don’t know why they are not black. Maybe there is no suitable black chemical.

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