• Question: how does the world know how to change from night to day and from day to night

    Asked by to Andrei, Ekbal, Gemma, Helen, Ruth on 16 Jun 2014. This question was also asked by .
    • Photo: Ekbal Hussain

      Ekbal Hussain answered on 16 Jun 2014:

      Hi @sinclairm,

      Imagine shining a torch on a football. You’ll notice that the torch only lights up one side of the ball and leaves the other side dark where there is a shadow. If you spin the ball, you’ll see that the light side now moves to the back and the dark side is now under the sunlight.

      This is exactly how the Earth works. The Earth is like the football and the sun is the torch. The side of the Earth that gets the light is day time and the other side is night time. And because the Earth spins in space, different parts of it change from light to dark, or day time and night time!

      You may not know this but your question has been at the centre of a huuuuge argument that happened a few hundred years ago. Some scientists thought that the Earth didn’t move and the sun went around it, making the changes from night to day.
      But in fact, we now know that it is actually the sun that stays still and the Earth that spins and moves around the sun.

    • Photo: Helen Gath

      Helen Gath answered on 16 Jun 2014:

      Hi! Yes it’s quite strange to think it can be day in parts of the world, yet night in time others. At lunch time in Britain, our part of the world faces the sun, whilst Australia, is in the dark. The earth keeps rotating, and as it rotates Britain is exposed less and less to the sun as it turns away from it, thus slowly getting darker and darker.
      In 24hrs, the planet completes one full rotation. Of course we don’t feel the earth spinning, it’s very slow and very smooth. This rotation has been happening since the universe was created, and it’s due a ‘gravitational pull’ between our planet and the sun that has kept on spinning! So fortunately, no one has to remember, it happens naturally.
      Try taking a football and holding it next to a lamp in a darkened room. Slowly rotate the ball around and you’ll see that parts of the ball that were once exposed to the lamp slowly move around away from the light and are finally on the other side of the lamp, and therefore in darkness. A bit of a rough comparison, but it gives you an idea. If your classroom has a Globe, try it with that and you could follow particular countries. That way, you’ll see how some countries are in the dark and some are in the light at the same moment in time. Pretty cool.

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