Newbie
All this silly talk of our demise Dec 2012 made me wonder. If the moon's orbit changes, even a wee bit, wouldn't that potentially change our tides into some huge tsunami? I've seen the tidal bore(sp) in the Bay of Fundy in Nova Scotia and it's quite amazing.
Established Member
I doubt it would cause a tsunami, mostly because of what a tsunami is. I can definatly see it changing the tidal pattern some what, since you would be changing both the apogee and perigee of the Moon, which in turn would change the amount of gravity we felt. It would also depend on how much you moved the orbit. If you are talking a distance of change, say like 10,000 km at perigee it would not be a very pronounced effect. But if you changed it by 75,000 km, it would be a pretty significant effect.
I hope I am right in this. I am sure someone will let me know if I am not.
Order of Kilopi
I pray the Moon's orbit stays just where it is. It would take a fantastic event to change the moon's orbit...ie asteroid strike, and it would serve no one well . Not now, and not later.
The Moon. It's a very good thing. And it serves us well.
Best regards,
Dan
Order of Kilopi
A wee bit of change in the orbit would result in a wee bit of change in the tides, which are fairly small anyway. The tides, top to bottom, are only a bit more than a meter. Local geography, like at the Bay of Fundy, amplifies them some. They'd be amplified a wee bit more.Originally Posted by weelie
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And how exactly does one nudge the moon's orbit a wee bit? For the change in orbit to have a dramatic, sudden effect on the tides, it would require a dramatic, sudden change in the orbit, and that would require a lot of force/energy. How exactly is this force applied? Where does it come from? I also suspect that the likely cause of such a change (such as a major meteor strike on the moon) would have many other consequence.
By the way weelie, welcome to BAUT.
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Actually, at one time our moon was much closer than it is today. And the daily tides were considerably greater than they are today. But the moon's orbit is outside the Roche radius, which means that it is slowly moving away from us. So, I don't think we have anything to worry about.
Eric
Order of Kilopi
Correction: Being outside the Roche radius only means that Earth's gravity gradient will not tear the Moon apart.Actually, at one time our moon was much closer than it is today. And the daily tides were considerably greater than they are today. But the moon's orbit is outside the Roche radius, which means that it is slowly moving away from us. So, I don't think we have anything to worry about.
Eric
Tidal interation causes the Moon to spiral out gradually as long as the Earth's spin period is shorter than the Moon's orbital period. If we could somehow slow the spin down to less than one rotation per month, the Moon would start spiraling in. It has nothing to do with the Roche radius.
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I stand corrected! Thank you for the explanation.
Eric
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I will say this though, Hornblower: if the moon had been inside the Roche radius it would have been torn apart by tidal forces, as you have said, or never formed in the first place and the debris would have slowly spiraled downward towards the Earth, just as Saturn's rings are in the process of doing. I guess that's what I meant to say, but it's still early in the morning for me, and I'm still on my first cup of coffee. LOL
Eric
Order of Kilopi
Yes, your point is valid, but the radius you have in mind is the radius of geosynchronous orbit. We have telecommunications satellites at the radius, so you know the Moon is well outside that radius. So its orbit is being perturbed a "wee bit" all the time-- just very gradually. Which raises another point-- it's not just the amount of perturbation that matters, the timescale matters too. There is some timescale for the Earth's oceans to respond to changes, which is pretty much the timescale for a tsunami to cross the ocean (say about 6 hours, they are very fast). A perturbation in the Moon's orbit on that timescale would not need to be very large to have dramatic consequences, but as Swift points out, it would require an awful lot of energy to change the orbit of the Moon enough to matter in just 6 hours. If one is worrying about something big slamming into the Moon, for example, it's a lot more likely that it would slam into the Earth-- with more directly catastrophic consequences.
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An excellent point, Ken G!
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If anything has the power to 'nudge' the moon's orbit, you're going to have a LOT more to worry about than a bit of tidal shifting...
Established Member
LOL JustAFriend! That's very true!
Order of Kilopi
the moons orbit is changing every day - by a tiny tiny ammount - but it IS training.
Established Member
I forgot all about this in my explanation. Thanks for bring it up, Ken!
Last edited by NickW; 2009-Oct-28 at 06:17 PM. Reason: forgot a word
Order of Kilopi
What if a large body passed by outside of the orbit of the moon? Both the earth and moon would be accelerated, but the moon more so, so it would change the orbit, wouldn't it, without major effects?
As above, so below
Order of Kilopi
I think that's the issue about timescale, and what is meant by a "nudge". Gravitational interactions between some third body and the Moon would be quite slow unless it was a very close pass.
Order of Kilopi
Just for argument's sake, suppose that a body like Titan got thrown out of its own orbit and came cruising relatively slowly past the earth-moon system, and came close enough to the moon that it was not within the Roche limit, but still pretty close.
As above, so below
Order of Kilopi
If it came close enough to appreciably alter the Moon's orbit on less than about a 6 hour timescale, that would be tsunami city. If the interaction took much longer than that, the oceans would adjust and you wouldn't even notice it, except for areas where changes are magnified like the Bay of Fundy.
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