Without the Moon

[Sunny129]

Your explanation is what I took away from the Howstuffworks description-- that the moon is stretching the earth out, including its oceans, and that is manifest as the oceans bulging on both sides.

my mistake then...i guess i just didn't think that their description of "the earth being pulled away" from the oceans on the side of the earth opposite the moon was very clear. but as long as you understand it now, that's all that matters. :thumbsup:

 

[William Gaatjes]

this is a tough concept for many people to grasp...that's OK. i'll try to put it in layman's terms as best i can. the fact that the force of gravity changes with distance gives rise to the term "tidal" force. that is, tidal forces are really just differences in the force of gravity between one location and another. clearly the oceans facing the moon have a greater gravitational bond with the moon than the oceans on the side of the earth opposite the moon. while howstuffworks.com's explanation of the bulge on the opposite side of the earth isn't totally incorrect, IMO its a pretty poor explanation. the bottom line is that the moon pulls harder on everything closer to it (the oceans, the mountains, and the entire earth itself for that matter) than it pulls on anything that's farther away from it. that is, as you get progressively further away from the moon, so does its gravitational force on you get progressively weaker. hence the tidal force's ability to "stretch" things out along the axis of force (in this case, the force of gravity).

another example that helps alot in visualizing this concept is a body in the vicinity of a black hole, particularly a stellar mass black hole (as opposed to the super-massive black holes found at the centers of galaxies...but that's neither here nor there). black holes are known for their very disruptive tidal forces b/c their gravity is so strong. let us suppose you're falling toward a black hole feet first from very far away. you would not be able to notice the difference in the amount of gravity of the BH exerts at 10 billion miles out versus 9.9billion miles out for example. and yet during that time, you'll have fallen 100 million miles closer to the black hole - that's a long way to travel toward a massive object and not feel the change in gravitational force. but the closer you get to the BH, the greater its gravitational force becomes. eventually you'd get close enough to the BH to where the difference between the gravitation force pulling on your feet is significantly greater than the gravitational force pulling on your head. this is "tidal forces 101," and the closer you get to the BH, the greater the tidal forces become (and the greater the difference between the gravitational pull on your feet vs your head becomes). you will eventually get stretched out along the axis of force, and your feet will accelerate toward the BH at a greater rate than your head, stretching you out like a piece of spaghetti.

so that is why there is high tide on opposite sides of the earth at any given time. that is, the above explanation is why the earth (along with its oceans, since they are fluid) takes on an elongated shape along the axis of gravitational pull. i can see how some folks still might be cofused as to why all the oceans don't just flow to the side of the earth nearest the moon, but it just doesn't work that way. tidal forces have the tendency to stretch things out along the axis of force, giving matter farthest from the source of gravity the appearance that it is being stretched in the opposite direction, when really its getting pulled in the same direction as everything else - just less so b/c it is farther from the source of gravity.

IMHO That just does not make sense. The strength of gravity decreases with a factor of the distance squared. The earth should look asymmetric with your explanation, as for example like an egg. Not more or less symmetric as it seems.

I do find it amazing that the moons gravity is strong enough and the changes in distances (12000 miles diameter of the earth) is enough to account for the perceived effect, although the gravitational pull of the moon is not the only pulling force.

The earth is flattened because of centrifugal forces. That is an symmetric effect. Gravity is not symmetric. That we have tides on both sides has to do because the gravity of the moon is pulling on the water and the earth. But it is not the moon alone. Think of what is happening inside the earth when the moon pulls. ninjahedge is indeed right. The center of gravity from the earth changes because of the molten insides of the earth are moved around by the gravitational pull of the moon as well. Combining the moon and the earth, it is called the barycenter. And then we get the effect of the gravitational pull of the sun.

Gravitation on earth changes with differences in latitude as well. And if we could measure the whole planet, we would see that gravity changes on different positions during the 24 hour cycle of 1 rotation of earth and the moon cycle. And even during 1 full cycle around the sun. And it does not end there. It will change in a cycle for around 26000 years as well.

IMHO i still think there is some form of delay that accounts for an apparent shift because the earth wobbles because of the moon. The earth is not a perfect sphere with an uniform density. No use to model it that way.

 

[PsiStar]

http://solarsystem.nasa.gov/planets/profile.cfm?Object=Moon

FWIW, Nasa believes the moon "makes Earth a more livable planet by moderating our home planet's wobble on its axis".

Call me the doubting Thomas (separate thread for the equivalent meaning in other cultures is begging). But a google of "Moon makes Earth a more livable planet by moderating our home planet's wobble on its axis" returns a many cyclical self referring links. All I wanted to know who said it 1st! Facts deserve the credit of the individual & not an "institution". Still looking ... as I don't think it logical.

However, I did find the comment, then immediately lost it ARRrgh! That the wobble is due to imbalance of the mass of the earth. Now. Doesn't that actually make sense?!?! Still looking for that, but maybe not tonight.

Because it is on a NASA web site does not mean that it came from authority. The email addresses of orbital scientists are available on the web & I may email one or a couple.

 

[Throckmorton]

Call me the doubting Thomas (separate thread for the equivalent meaning in other cultures is begging). But a google of "Moon makes Earth a more livable planet by moderating our home planet's wobble on its axis" returns a many cyclical self referring links. All I wanted to know who said it 1st! Facts deserve the credit of the individual & not an "institution". Still looking ... as I don't think it logical.

However, I did find the comment, then immediately lost it ARRrgh! That the wobble is due to imbalance of the mass of the earth. Now. Doesn't that actually make sense?!?! Still looking for that, but maybe not tonight.

Because it is on a NASA web site does not mean that it came from authority. The email addresses of orbital scientists are available on the web & I may email one or a couple.

Maybe the moon just forces the wobble to align with its orbit

 

[Sunny129]

IMHO That just does not make sense. The strength of gravity decreases with a factor of the distance squared. The earth should look asymmetric with your explanation, as for example like an egg. Not more or less symmetric as it seems.

I do find it amazing that the moons gravity is strong enough and the changes in distances (12000 miles diameter of the earth) is enough to account for the perceived effect, although the gravitational pull of the moon is not the only pulling force.

The earth is flattened because of centrifugal forces. That is an symmetric effect. Gravity is not symmetric. That we have tides on both sides has to do because the gravity of the moon is pulling on the water and the earth. But it is not the moon alone. Think of what is happening inside the earth when the moon pulls. ninjahedge is indeed right. The center of gravity from the earth changes because of the molten insides of the earth are moved around by the gravitational pull of the moon as well. Combining the moon and the earth, it is called the barycenter. And then we get the effect of the gravitational pull of the sun.

Gravitation on earth changes with differences in latitude as well. And if we could measure the whole planet, we would see that gravity changes on different positions during the 24 hour cycle of 1 rotation of earth and the moon cycle. And even during 1 full cycle around the sun. And it does not end there. It will change in a cycle for around 26000 years as well.

IMHO i still think there is some form of delay that accounts for an apparent shift because the earth wobbles because of the moon. The earth is not a perfect sphere with an uniform density. No use to model it that way.

you've taken what i said quite too literally...or just misinterpreted some of it. i never said that the earth is deformed by the moon's gravitational pull. i said the earth experiences it as much as its oceans do. of course its not strong enough to deform the earth! that's why it only deforms the oceans which we experience as the tides. i'm also quite aware that the earth is somewhat flattened into a non-spherical, but symmetrical oblate spheroid due to equatorial bulging caused by its own rotation.

another thing i am aware of is that fact that the moon isn't the only thing in our solar system pulling on the earth, its oceans, and everything else on it gravitationally. i also don't disagree with ninjahedge that, despite having a constant mass, the earth's center of gravity can wander. and there's no doubt that it has tidal influences on the oceans, as does the gravitational pull of the sun. but those influences are insignificant compared to the moon's influence. the tides we recognize as "high tide" and "low tide" are indeed a result of the moon's gravitational influence. think about it...even though the earth's center of gravity and the sun influence the tides gravitationally, the tidal bulges we see are constantly and always aligned with the moon, not the sun or the earth's wandering CoG. that's b/c, due to the given masses and vicinities of various bodies in the solar system, the moon ends up exerting the strongest gravitational influence on our oceans.

i understand that gravity changes with latitude, and i'm quite familiar with the daily, luner, and annual cycles, as well as the 26,000-year cycle during which the earth completes one full precession around its wobbling axis. regardless of those cycles, high-tide still seems to follow the moon around everywhere. i'm not sure how you came to the conclusion that my description should result in an egg-shaped earth (were any gravitational forces strong enough to deform it in the first place present). the bottom line is that the moon influences the oceans more than any other heavenly body in the solar system by a long shot (including the earth's off-center CoG caused by the moon's gravity), or else we would see the tides occasionally deviate from alignment with the moon. as you mentioned above, the force of gravity is inversely proportional to the distance squared. and like i said at the end of my first post, because of this difference in gravitational influence on the side of the earth nearest the moon and that of the side opposite the moon, we get tidal bugles on BOTH sides of the earth, as aligned with the moon. again, intuition may tell some people that there should only be a tidal bulge on the side of the earth nearest the moon, but the gravitational differential between the near and sides of the earth (with respect to the moon) is enough to cause the tidal bulge on the far side. that's just how tidal forces work.

 

[DrPizza]

For what it's worth, the bulge in the water isn't directly toward the moon. The bulge of the water actually leads the moon by about 10 degrees due to the earth spinning faster than the moon is going around the earth.

 

[Sunny129]

For what it's worth, the bulge in the water isn't directly toward the moon. The bulge of the water actually leads the moon by about 10 degrees due to the earth spinning faster than the moon is going around the earth.

right...i'm just leaving that part out for simplicity's sake. if we take that fact into account however, we can still see that the tidal bulges are constantly leading the moon by ~10°. while this fact makes things slightly more complex, it still fits with the idea that the tidal bulges more or less maintain a constant orientation with respect to the position of the moon at any given time, and are therefore most directly a result of the moon's gravitational pull.

 

[Biftheunderstudy]

Hence why the moon is tidally locked to Earth (it shows the same face to us all the time). Its interesting to see what happens in other systems with tides, such as, one of Jupiter's moons Io. I think Mercury is in a 3:2 tidal lock with the sun too.

The tidal bulge being ahead of the moon is what is causing:
a. the Earth's rotation to slow
b. the moon's orbit to increase

Also interesting to point out, black holes do indeed have ridiculous tidal forces near their event horizon...but this scales as the inverse of the mass. The supermassive blackholes at the centres of galaxies ought to have very weak tidal forces, you could cross the event horizon and not even notice.

 

[PsiStar]

The use of "tidal bulge" of latter emails is confusing me as is "tidally locked".

I am merely an amateur student of planetary science and very inconsistent at that. As an engineer & constantly trying to understand my customers' incorrect use of technical terms, I have to object.

Tidal bulge due to the moon lags the moon's position & cannot be ahead of the moon. "Tidal age" may be as much as 2 days behind the moon's position in fact due to ocean currents, the phasing of the currents, & geological formations. But it will lag.

Tidal lock between the earth & the moon will not occur ... contrary to how some use term... for billions of years. Regardless of the when, *now* is wrong.

Last, if there had been no moon, ever. There still would have been tides because of the sun's gravity. The sun's gravity is 46% (commonly found value) of the influence of the moon, but still would have and does have a tidal influence.

Come on guys. This information is not that hard to find ... google/bing/ask ... are not hard to use.

 

[Biftheunderstudy]

I may have been confused about forward/behind aspect of the tidal bulge, in any case, the outcome was correct. The Earth is dragging the bulge and thus slowing its rotation while giving angular momentum to the moon and increasing its orbital separation.

The moon is indeed tidally locked to the Earth, the reverse is not true though.

Back to the question though, its a difficult thing to answer since we don't really know how the moon has affected life on Earth. You just need to sit down and try to think of all the things related to the moon and its phases etc. Its orbit is regular enough that you can make a calendar based off of it, women's menstrual cycles are clearly correlated, moonlight etc.

Kind of mind boggling in how entwined it is.

 

[PsiStar]

Yes, to the earth dragging the bulge as a reason why tides lag the moon's position.

I guess I was splitting hairs about tidal lock as it can refer to either the moon or the earth ... and I was thinking about the earth. In the context of the earth's tides in the thread, I felt further confusion as others seemed to use the term both ways. "Tide & tidal" has multiple meanings or references thru this thread.

 

[uclabachelor]

Guy at work and me were debating what would happen if the moon was no longer there. Tide wave effect? No more "pull" of gravity from it etc.

What do you think the effect would be?

Let me nudge it out of earth orbit with some high powered lasers I have over the course of the next few decades and you'll find out.

 

[Sunny129]

Let me nudge it out of earth orbit with some high powered lasers I have over the course of the next few decades and you'll find out.

LOL...just be sure it isn't to the detriment of the human race

 

[vaylon]

If the moon were to suddenly disappear.
The tidal action of the planet would very quickly start to stabilize and within a couple of years would start to look like a lake.

The earths wobble would start to stabilize and season's would become much longer, some parts of the planet would most likely just have one kind of season.

Because of the lack of temperature variances caused by the seasons, oceanic currents would begin to shut down and warm water would remain in the equatorial regions and areas closer to the poles would get much colder. Ice age cold.

Weather patterns and storms would at first be very chaotic but would eventually fall into very predictable patterns. Eventually weather patterns would get to the point that change occurred on a decade basis instead of weekly or daily.

Millions of species would die off because their breeding and directional behavior is tied to lunar cycles. The ripples of their demise would propagate through the entire food chain, leading to mass starvation's and even more species dieing off.

The magma tidal action would also begin to stabilize creating less tectonic action, which in turn would mean less gasses being released into the atmosphere. Which would have a devastating effect on all life forms.

Over the course of a few million years the entire earth and its core would stabilize to the point that the core would no longer be able to produce a magnetic shield to protect the planet and the atmosphere would start to be stripped away by solar winds. Radiation levels would increase and most likely kill off any life that wasn't living deep within the earth.

Eventually the earth would look exactly like mars. The iron on the planet would oxidize in the atmosphere and become a red dust that would blow across the entire planet.

 

[OILFIELDTRASH]

Vaylon

What would stabilize the planets axis if the moon wasn't there? That alone debunks your whole theory.

 

[MrDudeMan]

Vaylon

What would stabilize the planets axis if the moon wasn't there? That alone debunks your whole theory.

You keep saying this but you really have no idea what you are actually saying. The barycenter of the two mass (earth and moon) system is the obvious thing that would change in terms of the earth's location on it's orbit. If it helps, picture spinning a sledgehammer by it's center of gravity. You'd be spinning it on your finger very close to the center of the head with a slight bias toward the side connected to the handle. If the handle suddenly detached, the center of mass would move to the center of the head. Assuming the object exerting the gravitational force is on the tip of your finger, the head of the sledgehammer would start rotating its center of mass around your finger tip. Now imagine the gravitational force is being exerted by an object at some distance and the sledgehammer is orbiting it while continuing to spin. The sledgehammer is spinning around it's barycenter as the handle is still attached. Now detach the handle and the head will continue to orbit with two changes: the mass of the system is now slightly different so the orbit will adjust itself to be in the lowest energy state and the center of mass of the system has now moved to the center of the head. The head will have a decayed oscillation around the center of its orbital path. The mass of the earth and moon is distributed similarly and would behave the same way.

The local system comprised of the earth and moon is affected as a single mass by external gravitational forces to a first order approximation. If the moon vanished, the earth would continue on a slightly different orbit (the moon was contributing some mass to the system after all) with a decaying oscillation around the new orbit just like the sledgehammer head after being detached from the handle. The wobble of the planet due to this event is merely transient and would eventually reach steady state.

Now, in terms of the earth wobbling uncontrollably - explain to me why it doesn't happen now if you think the moon is the only thing stopping it.

 

[Baasha]

Without the moon, I would think nutation would be impossible as well. The combination of the sun and moon, actually their tidal forces, causes nutation of the earth's axis.

 

[Sunny129]

Without the moon, I would think nutation would be impossible as well. The combination of the sun and moon, actually their tidal forces, causes nutation of the earth's axis.

i've never even heard of that, so i googled (wiki'd) it. i had no idea up until now that the movement of the rotational axis of such bodies was more complex than a perfect circle that is the precession itself. i guess you learn something new everyday lol...thanks for pointing that out :thumbsup:

 

[dinkumthinkum]

Here's a short letter to Nature by Laskar explaining a simulation of the Earth without the Moon:

http://www.nature.com/nature/journal/v361/n6413/abs/361615a0.html

Laskar also did some great work on Solar System simulations regarding long-term stability, if you are interested in that sort of thing.

 

[LiuKangBakinPie]

Sir, are you suggesting that we blow up the moon?

Would you miss it? Would you miss it?

 

[PsiStar]

Here's a short letter to Nature by Laskar explaining a simulation of the Earth without the Moon:

http://www.nature.com/nature/journal/v361/n6413/abs/361615a0.html

Laskar also did some great work on Solar System simulations regarding long-term stability, if you are interested in that sort of thing.

Now we are talking ... nice find

 

[OILFIELDTRASH]

You keep saying this but you really have no idea what you are actually saying.

No actually you don't know what you're saying. One of the guys in this thread was kind enough to give us this link.
http://www.nature.com/nature/journal/v361/n6413/abs/361615a0.html
Also the reason the earth would tilt would be from the gravity of the sun and other planets passing nearby. Thanks.

 

[LiuKangBakinPie]

The moon gives us the tides and it makes the rivers bendy