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Astronomy and Cosmology
Astronomy and Astrophysics
What Could Cause the Earth's Rotation to Dramatically Slow Down?
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[QUOTE="Ken G, post: 6861019, member: 116697"] What happens is, the Moon induces bulges into the Earth, both on the near and far sides of the planet. But since the Earth rotates faster than the Moon orbits, there is some delay in the bulges' ability to stay aligned with the Moon direction, so instead they get a bit ahead of the Moon. This should mean, for example, that the high tide is not when the Moon is directly overhead, but rather, when the Moon is slightly behind. That also means the bulge closer to the Moon (which has the largest back-reaction on the Moon) pulls the Moon slightly forward, as it is slightly out ahead of the line to the Moon. Any time an object receives a continuous but weak forward pull, it slowly moves into a wider, slower orbit. That orbit is still circular, just very gradually spiraling outward, with gradually increasing angular momentum. The excess angular momentum comes at the expense of Earth's spin, because that same forward pull on the Moon is a backward pull on the bulge that is closest to the Moon. That's the secular trend on long-term timescales, I'm talking about the possibility that astronomy classrooms over the next few decades might experience a steady increase in the Earth's spin over those (short) timescales, which would nevertheless be a little embarrassing for teachers who are saying that the Earth's spin is slowing down! Yes, it's not just the oceans, but water responds faster so most of the "bulge" is ocean. Agreed, this cannot be neglected and may be playing a key role in the latest fluctuations. Actually, believe it or not, when the Earth is tidally locked to the Moon, that will not be a permanent relationship-- the Moon will start coming back in again! That is because the Earth's spin period will at that point be 47 days, but its orbit will still be a year, so the Sun will be exerting tides on the system, which for some reason that is not completely obvious will end up starting the Moon back in. Not sure if it brings the Moon all the way back to be torn into a disk around the Earth or what happens there! Yes, the Moon has certainly had a pretty important effect, some even think the way it creates tidal pools helped life go from the ocean to the land. [/QUOTE]
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Astronomy and Cosmology
Astronomy and Astrophysics
What Could Cause the Earth's Rotation to Dramatically Slow Down?
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