What happens with no Moon?

ZeRoY

Hi guys,

Just a question that fascinates me, we often talk about a huge asteroid destroying the Earth, etc.. but what about if the Moon was to disappear suddenly? What would happen to Earth then - and I am not talking in years and century, I'm talking straight away, within the days, weeks that would follow Moon removal.

I have watched the very good BBC Documentary "Do we really need the Moon" but they don't answer this question of the Moon disappearing all of a sudden (unlikely i know...)

Anyone?

mike65

Well we would have more shallow tides (about half the current) and certain ocean currents would change or just stop. The ocean "bulge" at the equator would disappear so vast volumes of water would head north and south. Hard to know what the impact would be. Would the Arctic get swamped with warmer water and no longer freeze for a year or two?

The axis of rotation is stabilised by the moon so we'd get a "wobble" or drift which could have some dramatic climatic effects.

Green Mile

The earth would eventually stop rotating.

As the earth stops rotating the north and south polls would pull the sea from the equator to the north and south of the earth so we'd have land only around the centre of the earth.

Because the earth spins, the sea is pulled from the poles, like a string would counter gravity if it is swung around.

One side ofthe planet facing the sun would be scorched while the other side would befrozen. There would be no night and day

Rented Mule

I'd say the the surfing scene would suck.

Victor

Past and future disappearances would mean different changes.


Future:

There would be some changes - nights would be darker and slightly colder.

There would be no tides, which would change the environment in inter-tidal areas, probably resulting in those areas drying out with the loss of species that inhabit such areas.

With shipping, there would be some winners and some losers - the losers would probably be greater. The upper stretches of some tidal harbours / rivers would need to be dredged if they are to be kept in use. Other areas would probably need more frequent dredging as the scour effect of tides would disappear.

There would be less coastal erosion in rock areas, which could have knock-on effects in sand areas.


Past:

Life might not have evolved at all or as we now know it - I imagine tidal areas were important to fundamental to life evolving.

Our concept of months might be very different.

Monday would have a different name.

mike65 wrote: »

Well we would have more shallow tides (about half the current) and certain ocean currents would change or just stop. The ocean "bulge" at the equator would disappear so vast volumes of water would head north and south. Hard to know what the impact would be. Would the Arctic get swamped with warmer water and no longer freeze for a year or two?

The equatorial water would go to the tropics, the tropical water to the temperates and the temperate water to the poles, so it wouldn't be as extreme as you think.

Green Mile wrote: »

The earth would eventually stop rotating.

This will happen anyway - largely because of the moon. The friction caused by the tides is gradually slowing the spin. Removing the moon would mean we would continue spinning for longer.

As the earth stops rotating the north and south polls would pull the sea from the equator to the north and south of the earth so we'd have land only around the centre of the earth.

I think it would be more a matter of more land at the equator and less land at the poles as opposed to no land at the poles.

One side ofthe planet facing the sun would be scorched while the other side would befrozen. There would be no night and day

Not for a long time.

TaosHum

Green Mile wrote: »

The earth would eventually stop rotating.

When you say "Stop" do you mean it would come to a complete standstill or would it still rotate, just at a very slow pace?

Reason I ask is because Venus, with no moon, still rotates on its axis (although at a very slow speed).

seamus

Yeah, really hard to know with any kind of certainty. The orbit of the moon has an effect both on the earth's rotation and our position in space.

The best and oft-used illustration of this effect is to think of a hammer thrower spinning the hammer in place before they release it. The spin of the hammer causes the thrower to "wobble" on the spot. But at the same time the hammer also stabilises this spin because both objects are exerting a force on eachother. If you were to click your fingers and make the hammer disappear, the thrower would fall off balance and probably go spinning off the plate and into the nets.

This is most likely what would happen if the moon were to "disappear" - a "snapped elastic" effect would shift earth off its orbital trajectory. Which, needless to say would result fairly quickly in the death of all life.

On rotation, the moon is actually slowing down the earth's rotation.

Green Mile

Make a cup of tea and press play:
http://www.youtube.com/watch?v=wW_vmnfTeWM

Kxiii

TaosHum wrote: »

When you say "Stop" do you mean it would come to a complete standstill or would it still rotate, just at a very slow pace?

Reason I ask is because Venus, with no moon, still rotates on its axis (although at a very slow speed).

I don't think our rotation would stop in fact it would probably speed up and start to drift.

Venus' rotation is actually reversed it spins clockwise unlike most of the other planets. There are a few theories as to why this is, from tidal forces with the sun to a large impact in its early days much like the impact on Earth that crated the moon or like the impact that knock Uranus' axis off by over 90 degrees. The rotation on Venus is so slow that a day is actually longer than it's year.

the culture of deference

The moon is receding at about 3.8 cm per year.


The magnitude of tidal friction depends on the arrangement of the continents. In the past, the continents were arranged such that tidal friction, and thus the rates of earth's slowing and the moon's recession, would have been less. The earth's rotation has slowed at a rate of two seconds every 100,000 years (Eicher 1976).

The rate of earth's rotation in the distant past can be measured. Corals produce skeletons with both daily layers and yearly patterns, so we can count the number of days per year when the coral grew. Measurements of fossil corals from 180 to 400 million years ago show year lengths from 381 to 410 days, with older corals showing more days per year (Eicher 1976; Scrutton 1970; Wells 1963; 1970). Similarly, days per year can also be computed from growth patterns in mollusks (Pannella 1976; Scrutton 1978) and stromatolites (Mohr 1975; Pannella et al. 1968) and from sediment deposition patterns (Williams 1997). All such measurements are consistent with a gradual rate of earth's slowing for the last 650 million years.

The clocks based on the slowing of earth's rotation described above provide an independent method of dating geological layers

ZeRoY

Thanks guys, so no dramatic next day apocalypse then!

Victor

the culture of deference wrote: »

The rate of earth's rotation in the distant past can be measured. Corals produce skeletons with both daily layers and yearly patterns, so we can count the number of days per year when the coral grew. Measurements of fossil corals from 180 to 400 million years ago show year lengths from 381 to 410 days, with older corals showing more days per year (Eicher 1976; Scrutton 1970; Wells 1963; 1970). Similarly, days per year can also be computed from growth patterns in mollusks (Pannella 1976; Scrutton 1978) and stromatolites (Mohr 1975; Pannella et al. 1968) and from sediment deposition patterns (Williams 1997). All such measurements are consistent with a gradual rate of earth's slowing for the last 650 million years.

Another test they did was to subject people to a complete daylight and external time / information deficit - these people started living days that had 10 hours of sleep and 10 hours of waking, suggesting that when the genes controlling day/night behaviour developed, that this was the length of Earth's daily cycle.

Capt'n Midnight

isn't the moon resposible for the earths magnetic field ?

so massive auoras and then we run out of air to breath :eek:

(after a few billion years)




all the fish / worms that synch their reproductive cycles to the moon would have problems

Captain Chaos

Capt'n Midnight wrote: »

isn't the moon resposible for the earths magnetic field ?

No, our molten active core is. That's why Mars has no magnetic field, it's core partially solidified and stopped spinning a few billion years ago, up to that point it had a magnetic field like earth.

AlmightyCushion

the culture of deference wrote: »

The moon is receding at about 3.8 cm per year.

Never thought the moon and my hairline would have something in common.

Capt'n Midnight

this suggests that DNA would not have evolved without a good sized moon

http://www.newscientist.com/article/dn4786-no-moon-no-life-on-earth-suggests-theory.html


From clouds from DMSO and snowball earth and plate tectonics powered by CO2 from limestone from fossils we know that life has a feedback mechanism to keep itself going now, but it may have been touch and go early on

http://www.damninteresting.com/life-without-the-moon/
the moon acts as a gyroscope keeping us spinning on an even keel


We need to call NASA and get them back to the moon
http://www.astrobio.net/index.php?option=com_retrospection&task=detail&id=2507

When some of these impactors hit the Earth, the explosion caused rocks and dirt from Earth to shoot up and away from our planet. Some of that projected material flew all over the solar system, and some of it landed on the Moon. There could be a few hundred kilograms of Earth material per square kilometer of the Moon’s surface, buried under a few meters of lunar soil. It would be interesting to retrieve those rocks and bring back samples of the early Earth. Almost nothing from this time period has survived on the Earth because of tectonic recycling of the crust plates or because of atmospheric weathering. We would try to detect some organics within those rocks, and that could tell us about the history of organic chemistry on Earth. Some of these rocks could even have preserved fossils of life. Such rocks could help us look further back into the fossil record, which now stops at 3.5 billion years ago. This way, we could possibly learn about the emergence of life on Earth.

The crust of the Earth is also affected. The Moon’s tidal forcing causes significant heating and dissipation of energy to take place. Part of this energy is heating the Earth, and part of it is dissipated by forcing the Moon to recede from the Earth over time. There are people who propose that the tidal effect of the Moon may have helped trigger the convection on the Earth that led to the multi-plate tectonics.

locum-motion

From a sailor's POV;
We would only have one tidal cycle a day, not two.
And there would be no fortnightly spring tide/neap tide variation. Each tide would be the same height (much smaller than the tides we have now)

Zubeneschamali

locum-motion wrote: »

We would only have one tidal cycle a day, not two.

No, there would still be two tides, smaller than the ones we have now.

The two tides are not one caused by the sun and one by the moon, but because tidal forces distort the oceans into an ellipse: one bump on the side facing the Moon/Sun, one on the opposite side.

The tidal force due to the Sun is about half that due to the Moon, so we would get tides about one-third the height of the current spring tides.

Hidalgo

Warewolves would no longer be a problem

Capt'n Midnight

Hidalgo wrote: »

Warewolves would no longer be a problem

But that has to be balanced against darker nights which would benefit vampires and other denizens of the night.


Or like other species down here that synchronise their behaviour to the full moon, maybe they will just do it on random nights ?

Rasmus

ZeRoY wrote: »

Thanks guys, so no dramatic next day apocalypse then!

The proposals seem relatively apocalyptic to me!

ZeRoY

Rasmus wrote: »

The proposals seem relatively apocalyptic to me!

Yes but not in short term which was my original question!

Capt'n Midnight

ZeRoY wrote: »

Yes but not in short term which was my original question!

If the sun stopped shining in autumn after the harvests we'd survive for quite a while

coylemj

Tidal friction and the braking action of the Moon's gravity are both slowing down the Earth's rotation so no moon would simply reduce this slowdown, Earth would continue to rotate on it's axis for billions of years.

I don't believe the Moon has any effect on the Earth's rotational tilt so no moon will make no difference. The precession of the equinoxes has never been attributed to the Moon so no effect there either.

Tides themselves as already stated would continue but being caused by the Sun alone would fall within a much smaller range than before so ports which relied on high (even neap) tides to facilitate larger ships to enter/depart would be in trouble.

Solar Eclipse travel companies would go bust!

locum-motion

Zubeneschamali wrote: »

No, there would still be two tides, smaller than the ones we have now.

The two tides are not one caused by the sun and one by the moon, but because tidal forces distort the oceans into an ellipse: one bump on the side facing the Moon/Sun, one on the opposite side.

The tidal force due to the Sun is about half that due to the Moon, so we would get tides about one-third the height of the current spring tides.

Actually there are three of what you call bumps; two which don't move and one which does.
The biggest bump is on the side facing the moon, and is caused by the moon's gravity attracting water. The 2nd bump is on the side opposite the moon, and I'll explain what causes that one in a minute.
As a given point on the earth's surface rotates, it passes through these two bumps about 12.5 hours apart, and also through the lower water regions in between. This explains why we have 2 high + 2 low tides per 25 hours. Both of these tides are lunar.
The third bump is much smaller, and is caused by the sun's gravity attracting water. This bump 'moves' relative to the other two, and because it's smaller it's not perceived as a separate bump. Sometimes, it's lined up with one or other of the first two bumps, when it has the effect of making them more pronounced. This means that high tides are higher and low tides are lower, other wise known as 'Spring Tides'. Sometimes the third bump is lined up with the shallower bits between the other bumps. In that case, the shallows are less pronounced, so high tides aren't as high, and low tides aren't as low. These are 'Neap Tides'.
As the moon revolves around the earth on a cycle of about 29 days, imagine what happens to the sun-earth-moon angle (think of the centre of a clock as the earth, the little hand as the moon and big hand as the sun; the hands performs a 29 day version of 12 - 3 - 6 - 9 - 12. At "12" and "6" we have springs, at "9" and "3" we have neaps.)
The 'spring/neap' cycle is dependant on the interaction between the lunar tides and the sun's gravity.
If we had no moon, there would be no lunar bumps, only the solar bump. That bump would alway be on the sun's side of the earth, so there would be one single high tide at midday each day. As this bump is the smallest, the tides would be less extreme than we're used to.
Also, no interaction between solar/lunar tides means no spring/neap variation.

Now, as promised, the explanation for the existence of bump number two, the one opposite the moon.
Looking at the earth from above the pole, it would look like a wheel rotating around an axle. Thing is, though, that a wheel's axle is actually in the geometric centre of the wheel. However, the earth does not rotate around its geometric axis. The earth and moon behave as a binary system; the whole lot rotates around their combined axis, which is a line parallel to and quite close to but not exactly the same as the earth's geometric axis. Because of this, a point on earth opposite the moon is slightly further away from the axis of rotation than its corresponding point on the moons side. This slight wobble basically produces a second bulge on the opposite side, by centrifugal force.

Zubeneschamali

locum-motion wrote: »

Actually there are three of what you call bumps; two which don't move and one which does.

No, 4 bumps. One towards and one away from the moon, one towards and one away from the Sun.

The "centrifugal force" explanation is bogus. If you had a planet just like the Earth and a body the size of the Moon out in interstellar space, and neither of them was spinning or orbiting at all, and you just dropped them so that they attracted each other and fell towards each other, you would still see exactly the same bumps, with no rotation involved at all (until they crashed into each other!).

Gravity gradients pulls things into elliptical shapes, hence the bumps, and rotation is just a red herring. You can see the maths here, section: Case 1, the free fall

If we had no moon, there would be no lunar bumps, only the solar bump. That bump would alway be on the sun's side of the earth, so there would be one single high tide at midday each day.

Nope, still two bumps, and two tides.

Looking at the earth from above the pole, it would look like a wheel rotating around an axle. Thing is, though, that a wheel's axle is actually in the geometric centre of the wheel. However, the earth does not rotate around its geometric axis. The earth and moon behave as a binary system; the whole lot rotates around their combined axis, which is a line parallel to and quite close to but not exactly the same as the earth's geometric axis. Because of this, a point on earth opposite the moon is slightly further away from the axis of rotation than its corresponding point on the moons side. This slight wobble basically produces a second bulge on the opposite side, by centrifugal force.

This is totally wrong. The Earth does not spin around this "axis", it really does spin around its own geometric axis once a day. Once per lunar orbit, the Earth is displaced in a circle around this point.

If you look at the maths on this page (Case 2, the diagram labelled errato - wrong) you'll see that calculating the forces as if the earth was spinning around this common centre of motion with the moon gives entirely the wrong answers.

ZeRoY

Zubeneschamali wrote: »

You can see the maths here, section: Case 1, the free fall

....

If you look at the maths on this page

Ahhhhhhhhhhhhhhhhhhhhhhhhhhhh :eek:

I'll get my coat.

Zubeneschamali

ZeRoY wrote: »

Ahhhhhhhhhhhhhhhhhhhhhhhhhhhh :eek:

Ok, forget the maths!

When people try to imagine this centrifugal force, they tend to think of the earth and moon whirling around each other, slinging the Earth's oceans to the side far from the moon into a bulge. That's not how it works.

The earth doesn't spin with the moon, it is moved in a circle. Think of the motion your hand makes if you are polishing your car or a table with a cloth: your hand moves in a circle but it is not spinning around an axis. The centrifugal force due to this motion is the same everywhere on (and inside!) the Earth, and it is exactly equal to the gravitational force due to the moon at the centre of the Earth (or the Earth and Moon would be pulled together or fly apart).

On the side nearest the moon, the force of gravity from the moon is slightly larger than this centrifugal force leaving a very small tidal force towards the moon. At the centre, the forces cancel, so the centres of the Earth and Moon to not move closer or further apart due to this force. On the side furthest from the moon, the force of gravity from the moon, is slightly weaker, leaving an equally small tidal force aimed away from the moon.

The exact same diagram can be drawn with the Sun and Earth. Without the Moon, the oceans would still form an ellipse, giving the double bump and two tides.

Capt'n Midnight

back in the day the moon was only half the distance it is away

which would have meant massive tides ( ie. the rest of the world would get what we consider normal tides and we'd have whoppers )

cba looking up the formula for tides but it'd interesting to see what we would have had with a faster spinning globe

locum-motion

The explanation I posted above for the existence of bulge no two is the one I found a few years ago when I went looking for it (or at least, my attempt to put it into words)
After posting last night, I went looking for it again to link to it as a reference for my post, and I couldn't find it. Having (thus far) read the intro to what you posted back, I'm prepared to admit that I could have been wrong. I'll read more later when I've time; it looks interesting, though.

(On the bit he says in the intro paragraph about the non-existence of centrifugal force:
Yes, I did leaving cert physics, so I am aware that technically centrifugal force doesn't exist. I know that a moving object will continue to move in a straight line and a constant rate under its own inertia unless a centripetal force is applied to it to make it circle around an axis. However, the phrase 'centrifugal force' is much easier to use than 'the tendency of a moving object to continue moving at a constant velocity unless a centripetal force is applied.' When one talks about centrifugal force, we all know what is meant!)

Zubeneschamali

locum-motion wrote: »

(On the bit he says in the intro paragraph about the non-existence of centrifugal force)

Yeah, I think that stuff is overdone, we all know what a centrifugal force is, we've felt it.

But the page is right that most people get the wrong idea when they read that the second tidal bulge is due to a centrifugal force.