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Asked by Izzywizzy to Daniel, Hannah, Maggie, Ry, Scott on 10 Nov 2017.
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Maggie Lieu answered on 10 Nov 2017:
Its not really getting pulled by anything but what keeps the moon in orbit around the Earth is the Earth’s gravity. But the Earth isn’t a perfect sphere. It’s flatter at the north and south pole and it bulges out at the equator. Because the Earth is spinning, the equator is getting fatter and fatter and the poles are getting flatter. This means there is more gravity at the poles (which are closer to the center of the Earth) than at the equator. As the Earth’s gravity is getting weaker at the equator the moon moves further away… but its a very tiny amount!
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Ry Cutter answered on 10 Nov 2017:
Maggie has it covered!
The moon is leaving at about 4cm per year. We won’t really notice a change in our lifetime, but after a 10 million years the moon will look a lot smaller in the sky! -
Hannah Middleton answered on 12 Nov 2017:
Yes, it’s to do with the interaction between the Earth’s tides and the moon.
The moon is kept in orbit around the Earth by the Earth’s gravity, but the moon also exerts a force of gravity back on the Earth. This effect causes the tides on the Earth, because the moon is pulling on the Earth’s oceans and making the water bulge out a bit. The effect of this bulge means that the Earth is slowing down (and loosing some energy). Some of the energy that the Earth is loosing gets transfered to the moon, and causes the moon to go into a higher orbit. Over time, this slowing down is actually also making our days longer on the Earth!
Eventually the Earth and the moon could become “tidally locked”. This means that the same side of the Earth will always face the same side of the moon. At the moment, we always see the same side of the moon from Earth, so eventually the moon would always see the same side of the Earth. But this process takes a long time and the Sun may expand and engulf the Earth and moon in 5 billion years time before the tidal locking happens!
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Scott Melville answered on 13 Nov 2017:
The way that we know this is happening is by bouncing a laser off of some mirrors left on the Moon by the astronauts. Because we know how fast the laser beam travels, we can time how long it takes to return to Earth, and then work out a really accurate distance to the Moon. We’ve been doing this for years, and noticed that the distance is slowly increasing 🙂
This is a really neat experiment, it’s a really strong constraint on theories of gravity, and you could almost do it in your garden if you had a big enough laser (they do it on a roof in the Big Bang Theory, I think)
Comments
Izzywizzy commented on :
Oh ok. Thank you.
Izzywizzy commented on :
Thank you very much!