• Question: why do planets orbit the sun?

    Asked by 622gdna29 to David, Daniel, Arthur on 10 Nov 2014.
    • Photo: Arthur Dyer

      Arthur Dyer answered on 10 Nov 2014:

      Hi there,

      David will probably be able to give you an awesome answer to this question because he studies this area more than I have (No pressure David!!) but I’ll try and explain it as best I can.

      The basic reason why the planets revolve around, or orbit the sun is that the gravity of the Sun keeps them in their orbits. Just as the Moon orbits the Earth because of the pull of Earth’s gravity, the Earth orbits the Sun because of the pull of the Sun’s gravity.

      The Sun is basically pulling the Earth towards it.

      The next question might be “well why doesn’t the Earth just fall into the sun and we all burn?”… The reason that doesn’t happen is because of the Earth’s momentum. The Earth is sort of travelling sideways away from the Sun but the Sun keeps pulling the Earth towards it.

      A simple way to try this out yourself is to get two people to stand on a spot… they will be the sun… if you both grab onto the same arm of another person (who will be the Earth) and the person who is the Earth tries to run forwards they will end up going in a circle round the two people being the Sun! This is because the gravity of the Sun is holding the Earth in orbit despite the Earth wanting to travel in a different direction.

    • Photo: Daniel Parsons

      Daniel Parsons answered on 10 Nov 2014:

      Scientists think that the solar system was formed when a cloud of gas and dust in space was disturbed, maybe by the explosion of a nearby star which made waves in space. These waves squeezed the dust in the cloud and gravity pulled the gas and dust together and just like a dancer that spins faster as he or she pulls in her arms, the cloud began to spin faster as it collapsed. Eventually, the cloud grew denser and hotter in the centre forming the sun, with a disk of gas and dust surrounding it that was hot in the centre but cool at the edges. In the cloud of dust particles began to stick together and form clumps and some clumps got bigger and bigger eventually forming planets, spinning around the sun!
      So the Solar System was formed from a rotating cloud of gas and dust which spun around a newly forming star, our Sun, at its centre. The planets all formed from this spinning disk-shaped cloud, and continued this rotating course around the Sun after they were formed.
      The planets stay there because the force by which they are pulled towards the sun by gravity is equal to the force (due to their velocity) that is tending the planets to fly off into space (in the same way you spin a tennis ball attached to a string around your head and let go of it!)

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