What if...

[Legionary Jezza]

What is lets say the moon got destroyed tommorow doesn't matter how but theres nothing left not a moon rock at all, what would that do to the Earth?

[Gordon Freynman]

There is a whole episode of "The Universe" exactly about this, I don't remember much about it though. The most obvious effect would be on the tides, whose magnitude would be greatly weakened.

[Ancient Aliens]

We wouldn't be shielded from as much debris as we are, the tides would stop, the end of the lunar cycle would interfere with the behavioural patterns of many lifeforms, our days we be faster (about 6 hours long, which would undoubtedly change our time keeping devices), it would lead to more powerful meteorological phenomenon (storms), and it would have a huge impact on global climate.

[Nikitn]

it would throw Eart off its current orbit, basically changing global temperature and the length of a year. If the year becomes longer or shorter depends on if the moon disappears when it's closer to the sun or further away.


aliens, why exactly would the days become faster? the Earth's circulation is dependent on the moon?

[Ancient Aliens]

it would throw Eart off its current orbit, basically changing global temperature and the length of a year. If the year becomes longer or shorter depends on if the moon disappears when it's closer to the sun or further away.


aliens, why exactly would the days become faster? the Earth's circulation is dependent on the moon?

The massive gravity exerted by Luna on our planet vastly slows our spin-orbit resonance with the Sun.

[Gordon Freynman]

Here's The Universe's episode on this (there's 5 parts, but only the first part is really relevant to the topic):

[Admiral Piett]

So without the moon's gravitational pull, suddenly the Sun's pull on the ocean becomes stronger? That doesn't sound right. I seriously doubt it would cause a tidal wave. More likely the ocean's levels will flatten out, rising in some areas and dropping in others. The effects of the weather, seasons, and spin of the earth sound more plausible.

[Ancient Aliens]

So without the moon's gravitational pull, suddenly the Sun's pull on the ocean becomes stronger? That doesn't sound right. I seriously doubt it would cause a tidal wave. More likely the ocean's levels will flatten out, rising in some areas and dropping in others. The effects of the weather, seasons, and spin of the earth sound more plausible.

Yeah, the sun has little to no influence on Earth's tides. If anything, the tides would simply stop, which would still be catastrophic.

[Jack04]

Yeah, the sun has little to no influence on Earth's tides. If anything, the tides would simply stop, which would still be catastrophic.

The Sun contributes about 1/3 of the tidal forces on the Earth (if memory serves). Tidal forces go as ~1/r³, but the large mass difference between Sun and Moon almost compensates.

So, to do a bit of magical maths:

F_Sun is proportional to M_Sun/r_Sun³
F_Moon is proportional to M_Moon/r_Moon³

F_Sun/_FMoon = M_Sun/M_Moon x (r_Moon/r_Sun)³

M_Sun/M_Moon = 27 023 369.6 (says Google)
r_Moon/r_Sun = 0.00257356605

F_Sun/_FMoon = 0.460622828

So the tidal forces due to the Sun are about half the strength of those due to the Moon. Memory did serve (for once).

As a further comment, however, the tides we experience are actually effectively a wave. The forces due to the Moon and Sun are only enough to raise the sea by the order of a couple of centimetres. The tides we experience exist as a culmination of those forces acting consistently over long periods of time (which is why more isolated bodies of water, such as the Mediterranean Sea experience less tides).

[Ancient Aliens]

The Sun contributes about 1/3 of the tidal forces on the Earth (if memory serves). Tidal forces go as ~1/r³, but the large mass difference between Sun and Moon almost compensates.

So, to do a bit of magical maths:

F_Sun is proportional to M_Sun/r_Sun³
F_Moon is proportional to M_Moon/r_Moon³

F_Sun/_FMoon = M_Sun/M_Moon x (r_Moon/r_Sun)³

M_Sun/M_Moon = 27 023 369.6 (says Google)
r_Moon/r_Sun = 0.00257356605

F_Sun/_FMoon = 0.460622828

So the tidal forces due to the Sun are about half the strength of those due to the Moon. Memory did serve (for once).

As a further comment, however, the tides we experience are actually effectively a wave. The forces due to the Moon and Sun are only enough to raise the sea by the order of a couple of centimetres. The tides we experience exist as a culmination of those forces acting consistently over long periods of time (which is why more isolated bodies of water, such as the Mediterranean Sea experience less tides).

I stand corrected.

That being said, I'm fairly certain that having 3/4 of our tidal forces stripped from us would still result in a massive redistribution of coastal waters.

[Jack04]

I stand corrected.

That being said, I'm fairly certain that having 3/4 of our tidal forces stripped from us would still result in a massive redistribution of coastal waters.

More like 2/3 , but it would certainly cause a certain amount of havoc. However, since the tides actually primarily take the form of a wave, I'm not sure how dramatic (i.e. how fast) that redistribution would be. It might well take a while to take place. Tsunamis seem a little extreme.

[Irish Warrior]

It means Jupiter would start having a serious effect on us.

[Jack04]

It means Jupiter would start having a serious effect on us.

Jupiter's mass is 0.000954638698 times that of the Sun. It is also about 6 times as far away from Earth than the Sun.

As a proportion of the Sun's tidal influence (which, remember, is only 1/3 of the total tidal influence we experience), the tidal force exerted by Jupiter is approximately 4.48809477×10^-6.

So no, not really. Jupiter would remain insignificant.

[Irish Warrior]

Jupiter's mass is 0.000954638698 times that of the Sun. It is also about 6 times as far away from Earth than the Sun.

As a proportion of the Sun's tidal influence (which, remember, is only 1/3 of the total tidal influence we experience), the tidal force exerted by Jupiter is approximately 4.48809477×10^-6.

So no, not really. Jupiter would remain insignificant.

Well sir! I take your maths and raise you a smiley! Trumped no less!

But in all seriousness I believe that if we paint the moon purple, it will absorb more of the suns rays and somehow cool us!

But in all seriousness Pt. 2: The climate would get more erratic.

[Admiral Piett]

What about orbit? We know that without the moon, that the earth's spin will increase a little bit and the axis might tilt from time to time, but does the moon have a 'dragging' effect on our orbit?

[Time Commander Bob]

What about orbit? We know that without the moon, that the earth's spin will increase a little bit and the axis might tilt from time to time, but does the moon have a 'dragging' effect on our orbit?

The dragging of orbit due to the Moon's gravitational force would not be the main factor (since it pulls in every direction in the orbital plane of the Earth through its own orbit), but the loss of mass from the moon (which is small but more signficant). This is because angular momentum (H) needs to be conserved about the Sun and H = rmv, where r is the mass of the Earth-Moon system, r the radial distance from the Sun and v is the velocity perpendicular to r (strictly speaking H = r x mv, but we can leave vectors out of this for now)
So if the moon suddenly disappears when the Earth is at distance R from the Sun, then the mass of the system has decreased (by about 1% of the Earth) so the velocity must increase. This means the shape of the orbit would change, though the change would depend on where the moon disappears since the Earth's orbit is slightly elliptical. I think at both the points furthest and closest to the Sun it will make the ellipse wider but in different ways.

[Jack04]

If we're dealing with conservation laws, there's the small matter of where the hell all that mass/energy has gone

[Time Commander Bob]

If we're dealing with conservation laws, there's the small matter of where the hell all that mass/energy has gone

Yes, but angular momentum is still conserved so long as no torque is applied about the axis of rotation. Masses can be collected and expelled with angular momentum still conserved and provided the moon "simply disappears" then it will all be transferred to the Earth (of course the scenario is bizarre to begin with). The conservation of energy however, would probably require the moon to be looked at

[Jack04]

Yes, but angular momentum is still conserved so long as no torque is applied about the axis of rotation. Masses can be collected and expelled with angular momentum still conserved and provided the moon "simply disappears" then it will all be transferred to the Earth (of course the scenario is bizarre to begin with). The conservation of energy however, would probably require the moon to be looked at

No doubt. I was just pointing out how difficult a question it (the OP) is to answer. You have to in some way suspend elements which you would otherwise question (such as where the hell the mass/energy has gone).

[Nikitn]

The dragging of orbit due to the Moon's gravitational force would not be the main factor (since it pulls in every direction in the orbital plane of the Earth through its own orbit), but the loss of mass from the moon (which is small but more signficant). This is because angular momentum (H) needs to be conserved about the Sun and H = rmv, where r is the mass of the Earth-Moon system, r the radial distance from the Sun and v is the velocity perpendicular to r (strictly speaking H = r x mv, but we can leave vectors out of this for now)
So if the moon suddenly disappears when the Earth is at distance R from the Sun, then the mass of the system has decreased (by about 1% of the Earth) so the velocity must increase. This means the shape of the orbit would change, though the change would depend on where the moon disappears since the Earth's orbit is slightly elliptical. I think at both the points furthest and closest to the Sun it will make the ellipse wider but in different ways.

I haven't learned about angular momentum yet, I have very big trouble believing that this vector H would remain constant if 1/7 of the mass of a system disappeared. It just doesn't work like that, the momentum of a system is the sum of the momentums of all particles in the system.

If the orbit becomes longer or not depends on where the moon disappeared. The earth gets pulled on by the moon where a centrifugal force is acting upon it (while the earth has an angular velocity just as the moon does). As long as the centrifugal force is acting on earth then the earth's orbit around the sun won't move.