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What if the moon disappeared?

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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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