• Question: How do you know that planets are not as heavy as stars?

    Asked by anon-252361 to Tom, Ry, Chris on 4 May 2020.
    • Photo: Ry Cutter

      Ry Cutter answered on 4 May 2020: last edited 4 May 2020 2:00 pm

      We can see how much the planet can ‘move’ their star. Gravity is a two way tug of war between the planet and it’s star. You can imagine the star is so much heavier that it is swinging the poor planet around. The same is happening to the moon around Earth!
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      If two stars are next to each other, they weigh about the same. This means they’re both pulling an even amount, we see this as they spin around a point, the centre of mass.
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      This is one of the great things about gravity! It’s entirely dependant on the mass of two (or more) objects and their separation. So we can do lots of test to find put how much things weigh by watching how they move in space.
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      Great Question,
      Ry

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