• Question: Why is the sun really big even though its a star?

    Asked by afif to Austin, Kirsty, Nike on 21 Jun 2012.
    • Photo: Nike Dattani

      Nike Dattani answered on 21 Jun 2012:


      Stars look small to our eyes, but they can actually be VERY big. The reason why they look so small is because they are so far away. The reason why the sun looks big to us is because it is close to us. If we were closer to the other stars they’d look big too. If you went in a spaceship and looked at our sun, you’d see that it’s actually smaller than many of the stars in the sky !

    • Photo: Kirsty Ross

      Kirsty Ross answered on 22 Jun 2012:


      If the Sun weren’t big, its centre would not be hot enough to start fusing hydrogen atoms into helium atoms. This produces a lot of energy as the nucleus of a helum atom is less massive than four hydrogen atoms. The difference in mass radiates away in the form of electromagnetic energy and, as we all know, energy = mass time the square of the speed of light. 4000 tons of mass radiates as energy every second and without the brilliance of that energy the Sun wouldn’t be ‘the Sun’. It is the pressure of that energy which stops the Sun getting smaller. The Sun is a star and the definition of a star could be “anything which is more massive than 10 to the power of 28 (1 with 28 noughts after it) kilograms” – and that is pretty big!

      Even though the sun is 1,263,809 times bigger than earth, the sun is an average size star. There are stars that can be more than 4,000,000,000,000,000 (four quadrillion) times bigger than earth. That’s way bigger than the sun! Try dividing 4 quadrillion by 1,263,809 to see how much bigger than the sun some stars can be.

      As Nike says, stars in the size are a long way away compared to our sun, and so look tiny in comparison.

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