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What if the moon disappeared?

We recently received the following question about the moon:

would we miss the moon if it did not exist? I’m not asking what crazy improbable situation would be needed to remove the moon, just what the observable differences upon the Earth would be if there was no moon? Obviously there would be tidal differences, but would we have any other major effects I’m not aware of?

Matt A.
Minneapolis

Thanks for the question Matt, This was a fun topic to research.

There are more ramifications from a missing moon than you might realize.

The Tides

Of course you’re correct that there would be tidal differences but the details may surprise you.

Fist of all, the tides wouldn’t disappear. Everyone usually associates the moon with the tides but the sun contributes as well. These sun-only tides would be smaller of course; in fact they’d be about one third as high as they are today. They would also be very simplified as well, consisting of just a high tide and a low tide with no variation. This is because neap tides and spring tides would disappear since there would no longer be any moon to add to or subtract from the sun’s tidal influences.

Since Matt wanted to know the observable differences if the moon disappeared, I am creating an Observable Difference Factor scale from 0 – 10.

10–is easily observable by anyone not in a vegetative state.

1–is noticeable only by very alert scientists.

0–is not noticeable at all even by a post-singularity super-intelligent AI.

I give the tides an Observable Difference Factor of 9.

If you live or work near the coast and have a fully functional parietal lobe you will notice that the tides have changed.

Earth’s Spin

Did you know that a day on earth billions of years ago was only 6 hours long? Talk about days flying by.

Geologists know this by counting the growth rings in 400-million-year-old coral fossils and 3-billion-year-old stromatolites. Our days have been steadily lengthening because of a fascinating phenomenon call tidal breaking.    The huge high-tide bulge of water closest to the moon is never right under the moon because the earth’s spin is moving it away.  Gravity pulls the moon towards the bulge which speeds the moon up forcing it into a higher orbit. The bulge is also attracted to the moon so it tries to move toward it which is in a direction opposite to earth’s rotation. This increased friction slows the earth down. A more technical way to look at it is conservation of angular momentum. The total angular momentum of the earth/moon system must remain the same. The moon gains angular momentum as it moves away; therefore the earth must lose it to maintain this zero-sum game.

The bottom line then is that if the moon disappeared, the lengthening of our days would greatly slow down. It would still occur though due to tidal breaking caused by the sun.

I give this an Observable Difference Factor of 1.5

Scientists would notice this easily but some regular people would also notice that leap seconds stopped occurring every two years or so.

Rotational Axis

Picture the two dimensional path the earth takes around the sun. Now picture the axis upon which the earth spins. There is not a 90 degree angle between these lines. If that was the case, the earth would be a seasonless world. It is because the earth is tilted 23 1/2 degrees away from 90 degrees that I have to endure this bitterly cold winter for many months before spring-summer-fall arrives to reset my sanity back to baseline.

We take this angle for granted don’t we? It’s easy to think that this angle is fixed at the birth of the solar system and stays that way. It turns out though that our moon is a great axis of rotation stabilizer. Without it, the earth’s axis could potentially swing from 5 degrees to 40 degrees based on the various gravitational interactions with the other planets. Imagine what this would do to our weather and evolution. For those of you more into short-term thinking, you wouldn’t have to hold on to anything were this to happen.  This wobble could take thousands or hundreds of thousands of years to occur.

I give this an Observable Difference Factor of 1

Only scientists (and cloaked alien satellites) would notice this

Oceanic Redistribution

The only other significant effect I could find has to do with the altitude of the water in our oceans. Apparently, without the moons gravity, the water in our oceans would migrate a certain extent from the equator to the polar regions. It was unclear from my research how dramatic this effect would be.

I give this an Observable Difference Factor of somewhere between 5 and 9

This discussion seems to beg the question of what would the earth be like today if it never formed the moon in the first place after that Mars-sized object slammed into the early earth (imagine seeing that coming?).

I won’t go into detail but I’d like to briefly address the likely result.

An Earth day now would only be 8 hours long due to the isolated effects of  sun-earth tidal breaking.

A faster spinning earth would likely have horrific winds. Daily winds could reach 100 mph and hurricane winds would be quite nasty.

Evolution would be greatly impacted but it still would have occurred I believe. Life seems so tenacious and seems to have started as soon as it was possible but humans certainly wouldn’t be here if the moon never was. It seems likely that at the very least evolution would have been delayed or slowed greatly. With no moon there would be no mountainous tides early in earth history to scour the land every few hours and bring back to the primordial soup the critical chemical ingredients of life.

As I sit here contemplating these changes I am also grateful for some moon-based words that I would miss if they disappeared with the moon like lunatic and mooning.

19 comments to What if the moon disappeared?

  • Mchl

    How about most obvious difference? No more Moon landing hoax conspiracies!

    (OTOH, anyone saying that NASA never went to Moon would be right… tough trade)

  • moopet

    If you haven’t read it, I recommend Asimov’s “The Tragedy of the Moon” which contains essays about how the moon has affected our development and how it might have been otherwise.
    Well, I say I recommend it, I haven’t read it since I was a kid, but it’s Asimov, right? Right.

  • durnett

    If you haven’t seen it, I would recommend Space: 1999. It has no scientific or intellectual value at all, but it is fun!

  • Think of all the bad poetry we would be able to shed!

    Then again, think of what we’d miss: no creepy clouds covering the moon in horror movies, no werewolves, no CCR Bad Moon Rising song, and what would hit your eye like a big pizza pie?

    This is more serious than we thought.

  • jedischooldropout

    If the moon disappeared, the Moon Landing Hoax believers would be replaced by “What Did the Lizard Overlords Do With the Moon?” conspiracy theorists.

    ODF for Joe Average: 8.5
    ODF for Skeptics: 1.2

  • ziggy

    You left out that the moon may play a role in protecting us from some asteroid impacts, by either shepherding them away or taking the impact itself.

  • wb4

    “Scientists would notice this easily but some regular people would also notice that leap seconds stopped occurring every two years or so.”

    Correct me if I’m wrong, but I thought leap seconds were due to the fact that Earth’s rotation has slowed down since we officially defined the second. If the Earth stopped slowing down and spun at today’s rate from now on, wouldn’t we still have leap seconds just as often as we do now?

  • Hi wb4,

    Yes, the purpose of leap seconds is to help keep atomic time synchronized with solar time (UTC). The primary reason these times diverge is because of the tidal breaking. Without that, the divergence would be pretty slow. It might take many decades before another leap second would be warranted.

  • wb4

    “Without that, the divergence would be pretty slow. It might take many decades before another leap second would be warranted.”

    Why so long? I think we would continue to have leap seconds every couple years or so. As I understand it, Earth’s rotation would actually have to speed up for us to be able to reduce the rate of leap seconds. The reason we have leap seconds so frequently is not because Earth is slowing down currently, but rather because it has slowed down in the past. (The fact that it is slowing down currently means we will have leap seconds more often in the future than we do now.)

  • It could be so long because the other causes of tidal breaking like the sun’s tides and even the amount of snow cover is much smaller than the tidal breaking caused by the moon.

    I’ve read a lot about this in the past few days and, as usual, the science gets more complicated the deeper you look.

    Below is a pretty cogent overview of this issue from a NASA site.

    “Coordinated Universal Time (UTC) is the present day basis of all civilian time throughout the world…the length of the UTC second is defined in terms of an atomic transition of the element cesium and is accurate to approximately 1 ns (billionth of a second) per day. Because most daily life is still organized around the solar day, UTC was defined to closely parallel Universal Time. The two time systems are intrinsically incompatible, however, because UTC is uniform while UT is based on Earth’s rotation, which is gradually slowing. In order to keep the two times within 0.9 s of each other, a leap second is added to UTC about once every 12 to 18 months. ”
    http://eclipse.gsfc.nasa.gov/LEcat5/time.html

  • wb4

    Bob, I think you’re missing my point.

    Imagine that all causes of tidal breaking disappeared today, and that the planet’s speed of rotation was constant from now on. In that scenario, we would still need leap seconds just as often as we do now, about once every 12 to 18 months.

    It’s as if you have two clocks that run at different rates. Neither of them is slowing down, they simply run at different speeds. But you want to keep them synchronized with each other to within a couple of minutes, so every so often you have to nudge the minute hand on one of the clocks.

  • I’m sorry wb4. I can’t agree with your clock example.

    Why does neither of your clocks slow down? Does that mean you deny earth’s slowing rotation or that it is irrelevant?

    My version would go like this:
    Clock A(atomic) was created to match clock B (solar). This is the key concept.

    Clock B is slowing down. Therefore, clock A needs to be adjusted to stay synchronized.

    Which part of the NASA quote from my previous reply above do you disagree with?

    Sorry we can’t see eye-to-eye on this.

  • wb4

    No, I don’t deny that Earth’s rotation is slowing, nor do I think it is irrelevant. But, in the scenario where the moon disappears (and to keep things simple, let’s say that all other influences on Earth’s rotation vanish as well), Earth from that point on spins at a constant rate. In that scenario, there is no further slowing. It is this scenario that is analogous to the two clocks.

    To go with your clock A/B example:

    Clock A(atmoic) was created to match clock B(solar).

    In the time since clock A was created and synchronized with clock B, clock B has been slowing down (due to tidal breaking from the moon).

    Today, clock B stopped slowing down (the moon disappeared). Clock B now runs at a constant rate. But since it had been slowing down up to this point, it now ticks off seconds at a different rate than clock A. Therefore, clock A still needs to be adjusted periodically to stay synchronized.

  • Ok, I think we’re getting closer to crux of our disagreement.

    I understand that the earth has slowed since the initial synchronization of atomic and solar time. There is now a bigger difference than ever between an atomic second and a solar second. This difference though is minuscule after just a few decades of accumulation.

    I think you would be correct if the moon disappeared much farther in the future. By that time, the two different seconds would be so diverged that leap seconds (or maybe ‘divergence seconds’) would still need to be added regularly after earth stopped slowing.

    I just don’t think enough time has passed yet and earth’s slowing is by far the biggest contributor to leap seconds. Therefore, if the moon disappeared, leap seconds would still be needed but only at greater time intervals than they are needed now.

  • wb4

    I don’t understand your distinction between a ‘leap second’ and a ‘divergence second’. The reason that tidal breaking necessitates leap seconds is that it has caused Earth to spin at a slower rate now than it did when the second was defined to be 1/86400 of a mean solar day. (How else would tidal breaking lead to leap seconds, if not the fact that it has changed the rate of Earth’s spin?)

    According to the Wikipedia entry for ‘leap second’, the solar day becomes 1.7 ms longer per century, due mainly to tidal breaking. Even if we assume a current divergence of just 1 ms, that’s a difference of one second every 1000 days, or roughly one second every 3 years.

  • wb4

    Sorry, I should clarify, that should read:
    “Even if we assume a current divergence of just 1 ms / day, …”

  • wb4,

    I only threw in the term “divergence second” to distinguish between clock adjustments made when the earth was still slowing and when slowing stopped.

    I don’t think we should “assume” a current divergence of just 1 ms/day since this might just be the precise source of our confusion. That figure seems high to me.

  • wb4

    Hi Bob,

    According to the Time Service Department of the U.S. Naval Observatory, the current divergence is actually more like 2 ms/day. I took that number from here:

    http://tycho.usno.navy.mil/leapsec.html

    That yields an accumulated divergence of 1 second about every 500 days, which jibes nicely with the current leap second rate of one every 12 to 18 months.

    If you can answer this question (which I believe is key to our disagreement), then we should have a resolution:

    By what mechanism does tidal braking cause solar time and atomic time to diverge, necessitating a leap second?

    My understanding is that the tidal braking over time causes Earth to rotate at a slower and slower rate. It is this slower rate of spin, compared with the rate of an atomic clock, that causes the two to diverge, requiring occasional adjustments to atomic time. All of my previous arguments in this thread follow from that understanding.

    If you know if an additional mechanism by which tidal braking causes atomic time and solar time to diverge, I’d love to hear it.

  • wb4

    My previous comment has been in moderation limbo for 2 days, I guess because it has a hyperlink in it. Here it is again, without the hyperlink.

    According to the Time Service Department of the U.S. Naval Observatory, the current divergence is actually more like 2 ms/day. That yields an accumulated divergence of 1 second about every 500 days, which jibes nicely with the current leap second rate of one every 12 to 18 months.

    If you can answer this question (which I believe is key to our disagreement), then we should have a resolution:

    By what mechanism does tidal braking cause solar time and atomic time to diverge, necessitating a leap second?

    My understanding is that the tidal braking over time causes Earth to rotate at a slower and slower rate. It is this slower rate of spin, compared with the rate of an atomic clock, that causes the two to diverge, requiring occasional adjustments to atomic time. All of my previous arguments in this thread follow from that understanding.

    If you know of another mechanism by which tidal braking causes atomic time and solar time to diverge, I’d love to hear it.

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