• Question: If there are stars than grains of sand in the world, why is the sky not solid white?

    Asked by 454smag32 to Annette, Dave, Jaine, Julio, Mike on 14 Nov 2016.
    • Photo: Jaine Blayney

      Jaine Blayney answered on 14 Nov 2016:


      Close to the horizon, the sky appears white. However, because blue, as a colour, can travels in shorter waves, it is scattered more. So although the light starts out as white, because of the air molecules that it has to travel through, we see it as blue. See: http://spaceplace.nasa.gov/blue-sky/en/

    • Photo: Annette Neill

      Annette Neill answered on 16 Nov 2016:


      This is a rather complex question but in theory yes, the sky should be solid white given that for every grain of sand, there are 10 stars! There are a few reasons. The stars are not spiky, white objects like we draw them-they are filled with helium and hydrogen. They come in all sorts of colours. Because they are so far away from us, we see some of them and what we view are mostly white. Also because we are viewing stars at night, we view them as mostly white because we are using the rods in our retina (did you learn about rods and cones in your eyes? ) to view objects in dim light. Rods are photoreceptors that are more sensitive to light whereas the cones can distinguish between green red or blue. If you think about it, when you walk into a dark room at first you can’t see -that’s because you’re using mostly cones. Then you change to rods and you are no longer able to see colour!

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