The Moon wobbles

25 Comments
Posted December 4th, 2008 in Astronomy. Tags: , , , , , .
Lunar wobbling animation

This is what you get if you take a photo of the Moon every night for a month, then make a movie out of those pictures. The Moon’s phases aren’t surprising, but the Moon also appears to grow and shrink as it orbits the Earth. This happens because the Moon’s orbit is slightly elliptical; its distance to the Earth varies by about 10%.

Also, the Moon appears to “wobble” from left to right. That’s because the Earth’s gravity pulls harder on the Moon the closer it is to the Earth, so the Moon travels faster in its orbit when it’s closer to the Earth. The Moon’s rotation rate matches its average orbital speed (which is why we only see one face of the Moon), but its orbital speed varies during the orbit while its rotation rate remains fixed, so the Moon appears to wobble from left to right.

2009-08-10 Update: I’ve noticed that many people arrive at this article by googling moon wobbles. All the other sites on the first page claim that “moon wobbles” are responsible for explosions, mass-murder, earthquakes, terrorism, etc. Sadly, I need to emphasize that the wobbling I’m describing can’t possibly result in these kinds of ludicrous effects.

Last modified February 6th, 2012
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25 Responses to “The Moon wobbles”

  1. Also, if you look carefully, you’ll notice a slight up-down wobble as well.

    The origin of this wobble is totally different: it’s caused by the fact that the Moon’s axis of rotation isn’t quite perpendicular to the line that connects the Earth and the Moon.

    In other words, the Moon wobbles up and down for the same reason that the Earth experiences seasons.

  2. Interesting, it doesn’t surprise me that the moon wobbles to a certain extent. The 10% part surprised me, larger than I would’ve thought.

  3. Chanda Walker posted on 2009-07-04 at 17:14

    Beautiful visual. I’m thrilled to see this. Thanks for sharing.

    Have you ever researched why the moon looks so much larger at certain times of the year? For example, the harvest moon seems very much larger than a typical moon. I’ve always wanted to stop and figure this out but I’ve been just simply too lazy.

    • Beautiful visual. I’m thrilled to see this. Thanks for sharing.

      I can’t claim credit for the image, it’s from here.

      Have you ever researched why the moon looks so much larger at certain times of the year? For example, the harvest moon seems very much larger than a typical moon.

      I think you’re referring to the moon illusion where the moon appears larger and closer when it’s near the horizon rather than directly overhead. That’s probably a quirk of human vision rather than an inherent property of the moon’s orbit. I say this because the moon’s angular size is actually slightly larger when it’s directly overhead than when it’s on the horizon because we’re 1 earth radius closer to the moon when it’s directly overhead.

      There are quite a few hypotheses to explain this illusion, but most of them are inadequate. Here’s a very comprehensive overview where the author argues that “oculomotor micropsia” is responsible.

  4. Nice pic. The “Moon Wobbles” you describe are not the “Moon Wobbles” that mark disaster-prone phases in the world. These other Moon Wobbles were discovered in the 1930’s, when research by astrologer Carl Payne Tobey (1902-1980), the original editor of Astrology Magazine, revealed that disasters occur in cycles associated with the conjunction (0°), opposition (180°) and square (90°) from the Sun to the Moon’s Node. These powerful contacts occur when the Sun and the Node are in the same sign, or the opposing sign, or when the Sun is in a square aspect to the nodal axis. They are especially potent when the New Moon or Full Moon are square to the Nodes.

    I gather you are skeptical of the astrological POV, since you use the word “ludicrous” but you should read my article to get a better idea of what is actually being discussed.

    Best wishes
    Rob Tillett

    • I gather you are skeptical of the astrological POV, since you use the word “ludicrous”

      I’m skeptical of astrology because it’s been repeatedly disproven. It’s certainly not a science.

      … you should read my article to get a better idea of what is actually being discussed.

      … A highly unscientific analysis that makes no astrophysical sense and doesn’t even bother to calculate a p-value?

      Unless you use rigorous statistical methods, you’ll continue to draw bizarre conclusions from random noise, just like Carl Payne Tobey did.

      • truth seeker posted on 2009-11-02 at 10:37

        I think that if you choose not to see you will not see regardlesss of what is real. Science is a religion. So it is limited but do not try and tell that to the limited visioned scientist. And just as science is finally bumping up against religion and the truth is being revealed…there will always be those who refuse to see anything beyond their limited ability. If you cannot concieve of it you cannot see it. And by the way, rigorous statistical methods only prove that the scientist affects the experiment. There is no way of getting around it, we are all connected.

      • Science is a religion.

        Only in the sense that baldness is a hair color. I’ve previously defined religion and science; they seem completely different. If your definitions differ from mine, please tell me how– explicitly– so I can understand what you’re saying.

        So it is limited but do not try and tell that to the limited visioned scientist.

        There’s no need to tell us, because we already recognize that science is limited.

        And just as science is finally bumping up against religion and the truth is being revealed…

        I’ve noted that science isn’t capable of revealing truth at all. Science is limited to developing models that make unique predictions, which can then be compared to experiment.

        And by the way, rigorous statistical methods only prove that the scientist affects the experiment.

        How ironic that you write such an anti-scientific sentence on a computer– a device that works based on principles of modern quantum mechanics. Without rigorous experimentation, the flaws of classical physics wouldn’t have been discovered, so semiconductors probably wouldn’t have been invented. If generations of scientists hadn’t poured their lives into understanding the properties of light, the fiber-optic cables that transmitted your words to this website wouldn’t exist.

        I can only assume that you didn’t bother to read any of the links I provided in my last comment. They conclusively show that astrologers can’t make predictions that are more accurate than random chance.

      • John posted on 2010-01-17 at 09:39

        The moon and other planets and sun all have a force upon our planet. If the moon can move oceans than it can also slightly move thicker magma both creating massive preasure on our delicate outer crust. Major recorded events of catastrophes coralate with lunar and solar events and that is factual. And if meteor can have such long long orbits around earth and or sun this proves the far reaching effect of gravity. The moon is so massive and so close its effects are enourmous especially when there is a solar eclipse. The gravity is magnified and more concentrated. God says the planets are for a sign and wonders, read!!!!!!!!

      • The moon and other planets and sun all have a force upon our planet.

        Yes, scientists have known about universal gravitation since the time of Newton.

        If the moon can move oceans than it can also slightly move thicker magma both creating massive pressure on our delicate outer crust.

        Yes, the moon’s gravity causes body tides where the solid earth is compressed at tidal frequencies. One reason we notice tides in the ocean is because ocean tides are ~3x larger than body tides; what we actually observe at the beach is the difference between the ocean tide in the water and the body tide of the beach itself.

        But this is well established in mainstream science, and has nothing to do with these ridiculous astrology claims.

        Major recorded events of catastrophes correlate with lunar and solar events and that is factual.

        Solar storms such as coronal mass ejections shorted out telegraph wires in 1859, shut down a Canadian power grid in 1989 and disrupted communications satellites in 1994. The near-complete lack of sun spots during 1645-1715– a period later called the Maunder Minimum– worsened a “Little Ice Age” on Earth.

        But, of course, that’s not what these astrologers are talking about. And there aren’t any lunar events that affect Earth aside from eclipses and regular variations in tide heights, all of which are accurately predicted by modern science.

        Instead of declaring your statement to be “factual” maybe you should consider providing evidence to back it up.

        And if meteor can have such long long orbits around earth and or sun this proves the far reaching effect of gravity.

        Not nearly as impressively as observations of galactic superclusters, which show that gravity reaches across billions of light years.

        Again, this is irrelevant. Physicists understand very well that gravity has infinite range, but we also know that it follows an inverse square law in the weak field approximation. One consequence is that the doctor in the delivery room can exert a larger gravitational force on a newborn baby than most planets (depending on how obese the doctor is and the exact distance to the baby).

        The moon is so massive and so close its effects are enormous especially when there is a solar eclipse.

        No, spring tides are larger whenever the moon is “new” (which means it’s dark, so it’s roughly in between the Sun and Earth.) It doesn’t have to be exactly in between the Sun and the Earth as in the case of a solar eclipse.

        For example, spring tides also occur whenever the moon is full (which means it’s entirely lit up, so it’s roughly on the other side of the Earth as the Sun.) That’s because, as I’ve discussed, high tides happen on both sides of the Earth simultaneously.

        The gravity is magnified and more concentrated.

        No. Just… no. Gravity isn’t ever magnified or concentrated. The spring tides I just discussed happen because the gravitational force vectors of the Moon and Sun add constructively, rather than partially canceling as in the case of neap tides.

        God says the planets are for a sign and wonders, read!!!!!!!!

        Maybe I should read all the rigorous, peer-reviewed sources you provided to back up these astrology claims? Oh, wait…

  5. Hunchback Jack posted on 2010-06-13 at 13:45

    Thank you for a page about the moon wobble that *doesn’t* have anything to do with astrology, earthquakes, or other pseudo scientific nonsense, but that actually explains why it appears to wobble.

    I got here via half a dozen of those other sites, and I was beginning to worry about our prospects as a species. Your page restored my confidence. :)

    HBJ

  6. TEDDY posted on 2011-03-17 at 11:43

    Have you heard of the Chaos affect? Buttlefly flaps wings.. hurricane … We are all connected in somewhere to the fabric of the universe and are one, entanglement – universe has been entangled as a single system right from the Big Bang, ergo the moon can and does have an effect on mass-murder, earthquakes, and sadly terrorism, etc. Notice Japan’s earthquake and Tsunami and riots around the world and economic collapse. No one is an island here. Gravity is one of the 4 fundamental forces of the universe, how can you or any scientist dismiss it as having no effect on our earth, I just don’t know.

    • Have you heard of the Chaos affect? Buttlefly flaps wings.. hurricane … We are all connected in somewhere to the fabric of the universe and are one, entanglement – universe has been entangled as a single system right from the Big Bang, ergo the moon can and does have an effect on mass-murder, earthquakes, and sadly terrorism, etc.

      I’ve previously explained (halfway through this comment) that quantum entanglement isn’t a license to speculate wildly.

      Notice Japan’s earthquake and Tsunami and riots around the world and economic collapse. No one is an island here.

      I’ve noticed those things, but haven’t noticed how they have anything to do with the moon.

      Gravity is one of the 4 fundamental forces of the universe, how can you or any scientist dismiss it as having no effect on our earth, I just don’t know.

      Ironically, you wrote this sentence right after this comment where I describe how the moon’s gravity not only causes tides in the ocean but also body tides in the continents of our earth. I then mentioned that this concept is well known in the mainstream scientific community. After decades of study, the effects of body tides on earthquakes just turned out to be relatively insignificant: “Practically speaking, you’ll never see any effect of lunar perigee. It’s somewhere between ‘It has no effect’ and ‘It’s so small you don’t see any effect.'”

      Furthermore, I’ve explained how the moon’s gravity causes tidal bulges on both sides of our earth, and how these tidal bulges are not only slowing down our earth’s rotation, they’re also causing the moon to move away from our earth.

      In fact, I’ve pointed out that my day job is using GRACE satellite data to refine our estimates of global ocean tides, which once again are caused by the moon’s (and the sun’s) gravity interacting with the coastlines/bathymetry of the ocean basins.

      Scientists are well aware that gravity is one of the four fundamental forces in the universe, and that the moon’s gravity has effects on our earth. We just disagree with astrologers when they make unscientific and unfalsifiable statements about the moon causing mass-murder and terrorism.

  7. Glen Mackie posted on 2011-03-29 at 20:12

    Does this wobble take into consideration the Earth’s wobble when photographing it? How do you eliminate the effect of our own wobble and get a clear picture of how the moon wobbles? (apologies if this is a stupid question). Thank you.

    • I’m not sure what you mean by the “Earth’s wobble”. The observed “wobble” of the moon is a vague term I used to refer to the fact that its orbit around Earth is elliptical, so it’s not always at the same distance from Earth or moving at the same speed.

      Technically, this is true for the Earth as well, in the sense that Earth’s orbit around the Sun is slightly elliptical (but note that this has nothing to do with the seasons.) However, that ellipticity has no effect on photographing the moon because in that sense the Earth-moon system moves as a single unit.

      There are phenomena like the Chandler wobble which very slightly affects Earth’s axis of rotation over a period of ~1.2 years. Earth’s axis of rotation also “nutates” over a period of ~18.6 years, and precesses over a period of ~26,000 years.

      These phenomena are relevant to geophysicists and professional astronomers, but:

      1. They’re so tiny that they don’t affect amateur photography of the moon.
      2. They change so slowly compared to the moon’s ~28 day orbital period that even if they were much larger, they still wouldn’t affect pictures taken over a single orbit of the moon.

      Note that I didn’t make that movie; it was made by Tom Ruen. His page has many more cool photos that are worth checking out.

      Thanks for asking the first genuine question in years, which is really the only criterion needed for a question to not be stupid. You’re clearly trying to understand the universe rather than trying to justify a pseudoscientific preconception, which makes you the one-eyed man in this absurd kingdom of the blind…

  8. mikal posted on 2011-09-27 at 06:25

    what’s offensive about western science is its arrogance.
    you don’t know what intuition is, and that is the tragic flaw of western thinking and certainly of western science. intuition plays a part in astrology — the astrology that Kepler, Galileo and many of your other predecessors in science came from. intuition. do you know what it is?

    i’m done trying to percieve you and yeah, i did come in from looking up moon wobbles. but it does say “dumb” at the top.

    yours is the sort of scientist that gives all their energy to the military-industrial complex and then swears that they are not personally responsible for the atrocity. a form of evil, i think i can say that.

    empiricists are limited thinkers who assume that anything they cannot find evidence for could not exist. often the fault is in their closed minds…

    • I’m sure my colleagues from China, Taiwan, Japan, Korea, Russia, Pakistan, the Czech Republic, India, Croatia, Australia and New Zealand will be relieved to hear that they’re not offensive, arrogant, closed-minded, hypocritical, evil limited thinkers.

      But, like me, I think they’ll be puzzled as to what “western” science is. There is only science: the attempt to explain all conceivable experimental evidence with a self-consistent theory that requires the fewest possible number of assumptions.

      intuition. do you know what it is?

      Yes. Several years ago I said: I’m not fundamentally opposed to using intuition to solve mysteries. Choosing hypotheses to test is notoriously subjective, so “gut instinct” serves well in that capacity. But intuition is only the first step towards knowledge; that intuited hypothesis still needs to be subjected to rigorous scrutiny.

  9. Tony V. posted on 2012-01-29 at 22:54

    Thanks for this great information. I’d seen this sequenced video before, but couldn’t seem to find the explanations behind it. I am curious to know if theoretically there would ever be a point in time that, as the orbit of the moon increases, the closer proximity of the moon’s orbit with that of Venus would cause orbital disturbances between them. My intuition is that the tidal effects that are causing the moon’s orbit to increase would be diminished due to distance long before the orbit would increase that much. My second guess is that before the moon’s orbit increases that much, our sun will expand into a red giant, consuming all the inner planets.

    Thanks again for the insight!

    Tony

  10. David posted on 2012-05-09 at 13:27

    I’ve heard and seen a lot of “end of world” stuff online lately talking about how the moon is shifting poles, etc. Although I don’t buy into this kind of hysteria, I did do a little online moon pick comparisons and there does appear to be a much more significant shift of the 2 dark spots from the right side all the way to the top. Recent moon pictures of the Super Moon on May 5 2012 show this most significantly as compaired to your moon video where he spots are on the right. Now they are on the top. This seems to be about a 90 degree shift. I’s say that’s significant. I am sure if there was anything to worry about every amateur and professional astronomer worldwide would be talking about it. I am sure it is basically a case of ignorance. Can you educate me?

    • If nothing else, GRAIL would’ve noticed a 90 degree shift in the moon’s rotational axis. Conservation of angular momentum strongly argues against such an event.

  11. M. Vang posted on 2012-08-06 at 22:01

    I came here looking for the wobble detected via laser bouncing off reflectors placed on the moon during Americas moon landings. The “wobble” I was searching for is thought to be caused by a large impact on the moon.

    Similar to one of your previous comments, I was wondering how this measurement of “wobble” might take into account whatever sort of wobble the Earth might have. Instead I found this site, which seems a rich comedy in the study of Astrology. I find it especially humorous that the name of Kepler was used to support Astrology. His strange notions led him to believe for years in celestial spheres, in privileged, perhaps sacred, perfect solids which hearken back to Plato. He only came to the correct answer of elliptical orbits after having the bravery to accept that the observed measurements of the orbits out weighted any personal desire that his pet theory would be correct.

    If you believe in astrology and use Kepler to support it, I suggest you learn more about the man. At the least watch the Carl Sagan Cosmos series in full.

  12. George (not an astronomer, just a safety guy) posted on 2012-08-20 at 15:12

    Great discussion! However, it’s important to note that there have been times when accepted scientific ideas have been overturned, and respected scientists have been completely wrong.

    Newton was a rigorous scientist. Much of modern physics relies on the laws of motion that he quantified. But as it turns out he was a little overconfident when he named his ‘universal’ law of gravitation. As Einstein showed early in the 19th century, that law isn’t quite universal. It needed an adjustment in circumstances that Newton couldn’t possibly have anticipated.

    Lord Kelvin was another overconfident scientist. Despite being responsible for some great work, he stepped outside his area of expertise to declare that radio would never be more than a curiosity, and that heavier than air flight was impossible. Today, both statements seem ridiculous. They don’t diminish his other work, but they serve as a reminder that you can’t know everything.

    To be clear, I’m not defending astrology. Any field of study that relies on coincidence and conjecture to ‘prove’ its postulates is not science, any more than an ancient priest’s assurance that, since the sun came back after every solstice when a ritual dance was performed, the dance is what brought back the sun.

    But we must always allow for the possibility that widely accepted ideas may need to be refined, or even discarded altogether, based on new evidence.

    On the other hand, when the vast majority of the world’s scientists say one thing, they’re much more likely to be right than wrong!

  13. Carlos posted on 2012-09-08 at 05:22

    Great site, clear well written science. Much appreciated.
    Also, I’m amazed that you bothered to answer the nutters.

  14. Don posted on 2012-12-23 at 20:25

    I’m kind of interested to know if the moon’s actual orbital wobble around the earth, not the visual effect wobble but it’s actual path around our planet, has reached it’s apex? I had read somewhere, not sure where, that 2012 (no not refering to Mayan predictions which we all know now not to be true finally) that we have 3 known wobble’s which all reach their apex, moon orbital path wobble, actual earth rotational wobble and earth orbital path (around the sun) wobble. Just wondering if you might know if the event had already occurred or is still due to occur.

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