• Question: In space why is the universe black when there are millions of stars (uncluding the sun) that lights up everywhere?

    Asked by danylok59931 to Ed, Hayley, Jason, Nathan, Sophie on 13 Mar 2013.
    • Photo: Hayley Evers-King

      Hayley Evers-King answered on 13 Mar 2013:

      This isn’t actually a very simple question to answer. There are a number of suggestions though:

      1. There are lots of stars but many are so far away from us that there light hasn’t had enough time to reach us yet.

      2. The universe is expanding, as stars move away from us, the colour of their light shifts – this is called the Doppler effect and its the same effect that you hear when an ambulance or car passes you (the sound changes pitch). It’s thought that the light from the stars moving away from us could be shifted so far that we can no longer see it.

      3. There is no substance in space for light to interact with. You can think of it a bit like air – you can’t see air unless there’s certain things in it – like water (this is partly why clouds are white and the sky and ocean are blue!). In space, there is nothing to absorb or scatter the light from the stars, so you just see the points of light where they are emitted (from the stars) or where they reflect, i.e. off planets etc.

    • Photo: Edward Bovill

      Edward Bovill answered on 13 Mar 2013:

      Hayley has answered this really well already, but there is one other reason for why the whole night sky isn’t shining with light from distant stars:

      There is a lot of dust and other matter in the universe that doesn’t shine, some clouds of intergalactic matter are so big they’re almost the same size as galaxies but without any stars of their own. This absorbs light from distant stars and so we cannot see them any more.

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