• Question: if your smart why does the planets orbit the sun?

    Asked by asiansupreme to Anil, Blanka, Cees, Emma, Mike on 26 Jun 2012. This question was also asked by edward321.
    • Photo: Michael Cook

      Michael Cook answered on 26 Jun 2012:

      I think the main reason is that the Sun is much, much larger than any of the planets. That means it has a stronger gravitational pull. Everything in the universe has a gravitational pull – the desk in front of you, the computer, even you! But things that are quite light (like the desk, the computer, and you) have very weak gravitational pulls.

      Huge things, like the Earth, can pull in tinier things for this reason (that’s why you stick to the floor instead of floating off into space – Earth is pulling you in with gravity, right?). Similarly, the Sun can pull the Earth towards it because it too is much much larger.

      In order for something to orbit something else, it has to move in two directions at once, sort of – it needs to move slightly away from the thing it’s orbiting, and at the same time it has to have a force pulling it towards the thing it’s orbiting. This second force is the reason why the Sun couldn’t orbit the Earth – the Earth isn’t strong enough to pull it in.

      I hope that wasn’t too garbled an answer! There’s a diagram I found to help here (it shows the moon orbiting earth): . The two arrows are the two forces I mentioned.

    • Photo: Blanka Sengerova

      Blanka Sengerova answered on 26 Jun 2012:

      What a great answer from Mike, I’ll second that. Imagine that the earth and other planets are being pulled into the sun by an invisible string. But in order for the string to stay taut, the planets muts also be moving in the direction at right angles to the string, otherwise the earth or other planets would just gradually come closer to the sun and end up plopping into it. Try it out with a tennis ball on a string sometime!

    • Photo: Emma Trantham

      Emma Trantham answered on 28 Jun 2012:

      I don’t think I can add anything to Mike and Blanka’s excellent answers