Forgot your password?
typodupeerror
Space Science

Low-Hanging Moon Explained 381

Posted by Zonk
from the watch-your-head dept.
gollum123 wrote to mention a BBC article which explains the low-hanging moon of the past few nights. From the article:"For the past few nights the moon has appeared larger than many people have seen it for almost 20 years. It is the world's largest optical illusion, and one of its most enduring mysteries. The mystery of the Moon Illusion, witnessed by millions of people this week, has puzzled great thinkers for centuries. There is still no agreed on explaination for why the moon appears bigger when it's on the horizon than when it's high in the night sky."
This discussion has been archived. No new comments can be posted.

Low-Hanging Moon Explained

Comments Filter:
  • by TripMaster Monkey (862126) * on Friday June 24, 2005 @07:22PM (#12905665)

    Good day, gentlemen. As you are no doubt aware, I have perfected a device capable of altering the orbital path of the moon. First of all, I must offer kudos on a most inspired cover story...'illusion' indeed...really, a first rate piece of propagan-da. Of course, you know it cannot last...

    You see, gentlemen, things will only get worse...my device, which I've dubbed 'the Lunatrix', will continue destablizing the moon's orbit, drawing it ever closer to our fragile planet. First, abnormally high tidal waves will decimate all costal regions...then, as the tidal influence grows steadily stronger, geological disruptions will occur on a global scale, tearing apart the earth's crust like fresh bread, releasing the liquid-hot mag-ma within. No place on the planet will be safe...civilization as you know it will cease to exist...that is...unless you pay me...

    One hundred billion kajillion fafillion dollaaars!!!

    <DramaticMusic>

    Gentlemen, you have my demands...peace out.
    • Will you take euros? And it'll have to be a check, I'm afraid.


      Besides, I happen to know the Lunatrix was only the third-place prize in the last Pepsi contest.

  • Obvious. (Score:3, Funny)

    by Anonymous Coward on Friday June 24, 2005 @07:22PM (#12905670)
    Duh! Because it's closer!
    • Actually... (Score:5, Interesting)

      by objekt (232270) on Friday June 24, 2005 @07:36PM (#12905787) Homepage
      Assuming a perfect non-eliptical orbit, the moon on the horizon is farther away than the moon directly overhead by almost half the diameter of the Earth.

      Additionally, I wrote a college term paper about this illusion and in my research I found the illusion to be less pronounced in denizens of mountainous areas who have less exposure to things like train tracks that extend straight into the horizon. Without that frame of reference, they are less likely to think of objects near the horizon as necessarily being very away.
      • Additionally, I wrote a college term paper about this illusion and in my research I found the illusion [of a large moon near the horizon] to be less pronounced in denizens of mountainous areas who have less exposure to things like train tracks that extend straight into the horizon. Without that frame of reference, they are less likely to think of objects near the horizon as necessarily being very away.

        Except your thesis seems to fail by inspection - because you are comparing apples to oranges. Denizens

        • Re:Actually... (Score:5, Informative)

          by tomhudson (43916) <.barbara.hudson. ... bara-hudson.com.> on Friday June 24, 2005 @08:12PM (#12906037) Journal
          Easy explanation:

          Step 1: look at the moon near the horizon

          Step 2: now, block out the horizon and all other objects with your hands, and look at the moon

          The moon looks MUCH smaller whe you frame it with your hands and block out the extraneous stuff.

          Also works with the sun, etc.

        • Except your thesis seems to fail by inspection - because you are comparing apples to oranges. Denizens of mountainous areas often don't see the horizon at all - their line of sight to it is blocked by said mountains. By the time the moon rises to a point where it is visible to them, it's long been above the horizon, and thus is past the point where the illusion occurs.

          You can show them the train tracks illusion on a piece of paper and they will be less receptive to it than a flatlander would be.
  • old news... (Score:5, Funny)

    by deft (253558) on Friday June 24, 2005 @07:23PM (#12905674) Homepage
    some guy who got gods powers is trying to get laid... apparently its taking longer than the last guy i saw try this one.
  • by JWSmythe (446288) * <jwsmythe@jws[ ]he.com ['myt' in gap]> on Friday June 24, 2005 @07:24PM (#12905679) Homepage Journal
    This is news?

    I was thinking the same thing a few nights ago, watching the moon rise
    over LA. Then I considered, "Near the ground, I consider it in proportion to the objects around it. In the sky, I have no reference"

    Great thinkers? Centuries? Bah.

    Now what they need to figure out is how to fix the pollution in LA. The
    moon is red until it gets above the smog. Well, that is if you're not
    *IN* the smog.
    • That's what I thought, until someone pointed out to me that the illusion goes away when you stand on your head.

      Guaranteed to make you look foolish, but it works.
      • by nofx_3 (40519) on Friday June 24, 2005 @07:48PM (#12905877)
        So what you are saying is that this "Moon Illusion" is simply an occipital lobe processing error? Makes sense to me, there are obviously intances where our brain is incapable of properly processing information. This [michaelbach.de] was the first hit on google. I recommend trying the full tour, its neat stuff.

        -kaplanfx
      • the illusion goes away when you stand on your head

        And the perception of depth goes away if you close one eye. And the appearance of continuous motion vanishes if you blink your eyes rapidly. In other words, if you literally change the way you are looking at the world, you will change the way your nervous system processes the light that enters your eye. Your example is intriguing, but not all that revealing.

        I won't hypothesize why what you said works (since I haven't tested it), but I will point out that
      • by hey! (33014)
        Well, if you're patient you can prove to yourself it isn't any bigger without standing on your head.

        The moon subtends about 2 solid degrees. By fortunate coincidence, this is more or less the same angle subtended by by most adult's fingers when their hand is held at arms length -- very rought it's true, but close enough.

        So, just hold your index finger at arms length. It will be wide enough, approximately, to just cover the moon. Remember how it looked. Then look for the moon later when it's higher in
    • by Laivincolmo (778355) on Friday June 24, 2005 @07:28PM (#12905716)
      I've heard however that the illusion even occurs while flying high in an airplane. A horizon of clouds really doesn't give much of a landmark to compare to.
      • The way I've heard it, humans subconsciously model the sky as a flattened dome. Thus, when presented with two objects of equal apparent size, one on the horizon and one at the zenith, the one on the horizon looks bigger (i.e. is perceived as having a larger actual size) because it's "farther away" than, yet appears to be just as big as, the object that is directly overhead (and thus "closer").
    • by toddbu (748790) on Friday June 24, 2005 @07:33PM (#12905760)
      There's a similar illusion with mountains. When I look at Mount Rainier between some large trees, it looks huge. When I look at it while driving down the highway, it doesn't look all that big. I actually find it disappointing to stand at the foot of the mountain. From that vantage point, it doesn't look all that impressive. Having climbed Mount St. Helens, looking down on a mountain from the top, it looks huge. It's really weird.
    • Near the ground, I consider it in proportion to the objects around it. In the sky, I have no reference

      Near the ground you compare it to objects on the horizon. Some of those objects are things you have experience with up close (like buildings, trees, and mountains). So you get a sense of scale. The moon appears to be just behind the horizon, making it gigantic (though nowhere as big as it really is).

      Far from the ground you compare it to other flying objects that you also occasionally see on the ground
    • by ahecht (567934) on Friday June 24, 2005 @08:32PM (#12906149) Homepage
      I'm pretty sure that it has nothing to do with reference.

      I actually figured the whole thing out after visiting both a Planetarium and a Bucky-Dome [bfi.org].

      The first clue came at the planetarium. At the top of the dome was a small circle. If you visually estimated the size of the circle, you would assume it is 1-2 feet across. However, according to the planetarium guy, it is actually 6 feet across.

      The second clue came at the Cinerama Dome. The dome, like all geodesics, is made up of identical hexagonal pieces. However, inside the dome, all the pieces look distorted and irregularly shaped.

      The key here is that while both domes are semi-spherical, when you are in them, they both look like they are much wider than they are tall (sort of a squashed sphere shape). Your brain, for some reason, assumes that things directly above you are closer, and that things near the horizon are further, so the dome looks misshapen. With an improper mental image of distance, the tiles look distorted due to perspective, and the circle looks smaller because it is further than it appears.

      Basically, what this means is that the moon is the correct size on the horizon, and this "bug" causes it to look too small when it is high in the sky.

      And, if you think about it, this bug makes perfect sense. Most things your brain would see (think primitive man on the savanah here) that are straight ahead are going to be far away, or at least 10 meters or so away, so your brain adjusts accordingly. Similarly, most things you see when looking down are close, on the scale of a couple of meters, so your brain also adjusts from that. Most things you see looking up are the sky, and with no frame of reference, your brain assumes that looking up is just like looking down (after all, looking forwards is the same as looking backwards). Therefore, your brain associated things on the horizon as far, and therefore bigger than they appear, and things up or down as close, and smaller than they appear.

      • by DavidTC (10147) <[slas45dxsvadiv. ... ] [neverbox.com]> on Saturday June 25, 2005 @12:38AM (#12907353) Homepage
        You pegged it. The 'comparing to other stuff' is a red herring, it's that out brain treats up and down distance completely wrong.

        We are completely incapable of estimating them, at all.

        I don't know if it has anything to do with looking down, but that's an interesting theory.

        But I have to point out that everything we can see up is either very close, maybe three hundred feet max, with most of it within ten, or was, for the vast majority of human existence, infinitely far away, like clouds and stars. So it's not just because downward is so close. Up is basically the same way, being very close, with a few weird exceptions for mountains. (Of course, down has the same exceptions.)

        Whereas we've always been able to see things miles away and verify they are, in fact, that far away.

        People think Douglas Adams' idea of a race that can't conceive of 'up' is a bit silly, but we have a fairly serious blind spot there.

        For example, we think mirrors flip you around left to right. Well...it's just as correct to think they've flipped you around up to down. If you flipped an image in the mirror up to down, the person would be correct, although standing on their head. (Or flipped them front to back, but that's understandable, as you can only see one side of that in a mirror, so how you'd 'flip' that is a bit abstract.)

        • by zCyl (14362)
          For example, we think mirrors flip you around left to right. Well...it's just as correct to think they've flipped you around up to down. If you flipped an image in the mirror up to down, the person would be correct, although standing on their head.

          Uh, no it's not. That would be silly. Look in a mirror, raise your hand, and try to conceive of the image of your hand going down. The reason mirrors flip left and right is because left and right are defined relative to which direction is forward, and mirrors
      • The question is WHY (Score:3, Interesting)

        by magi (91730)
        Basically, what this means is that the moon is the correct size on the horizon, and this "bug" causes it to look too small when it is high in the sky.

        I would like to propose a hypothesis why this is actually not a "bug" but has a purpose: gravity and hand-to-eye-coordination.

        Most of us may have noticed that when you throw things, the things won't keep going straight to that direction, but fall to ground. We are pretty good at throwing at things far away rather accurately. You don't need to calculate the
    • Now what they need to figure out is how to fix the pollution in LA.

      Move. No, seriously - get everyone and leave. Plant some trees on the way out and I think the smog would be gone in no time.

      I was going to say stop driving your cars, but I didn't want to seem like a smart ass
  • by shawn(at)fsu (447153) on Friday June 24, 2005 @07:24PM (#12905685) Homepage
    I heard on various shows that it's because it's closer to things that our mind knows are big when it's close to teh horizon, trees buildings towers etc. When it's high in the sky there is nothing around it.
    Some one on some show said that if you bend over doubled and look through your legs at the moon, no matter where it is in the sky it will appear large as well for the same reason
  • by Anonymous Coward on Friday June 24, 2005 @07:24PM (#12905688)
    For the past few nights the moon has appeared larger? Could this open some eyes and increase interest in alternative (Linux, Mac) offerings?
  • Too bad Princess Leia is away on that diplomatic mission and can't be here to see this.
  • Easy Fix (Score:5, Funny)

    by Laivincolmo (778355) on Friday June 24, 2005 @07:25PM (#12905698)
    If you bend over with your head between your legs and look at the moon upside down, the illusion disappears. (I'm being serious too!)
    • Re:Easy Fix (Score:3, Funny)

      by Lattitude (123015)
      When you're in that position, it's important to look at the correct moon...
      • Yeah, at first I was confused as to why he'd be modded "funny" when another poster said the same thing, basically.
    • Re:Easy Fix (Score:5, Interesting)

      by Council (514577) <`moc.liamg' `ta' `eornumr'> on Friday June 24, 2005 @08:01PM (#12905963) Homepage
      A lot of things change when you turn them upside down; I don't think it tells you much about the mechanism of the illusion; it's a wide-ranging and general visual processing hack.

      For example, frightening movies totally lose their atmosphere if you tilt your head 90 degrees so the TV is sideways. You can see everything going on, but the images aren't alarming. At least, that's what I've found.

      Read Mind Hacks [amazon.com] for some interesting stuff on visual processing. The rotating-during-scary-movie thing I first noticed as a little kid watching Jurassic Park, but in Mind Hacks I learned things about how we recognize rotated shapes -- we have to do a lot of processing to flip them over, and the time this takes is proportional to the angle. So I think we get the images with too much lag for the brain to do a lot of the post-post processing it usually does -- i.e. being frightened, comparing sizes properly, etc.

      The visual parts of the brain are surprisingly dependent on orientation.
  • by Sv-Manowar (772313) on Friday June 24, 2005 @07:27PM (#12905708) Homepage Journal
    It's amazing how much of how our brains and sight work together to recognize object's size and position creates these kinds of illusions. It just shows that even a finely tuned system that works well in everyday use can be caught out, and how because we rely on our vision to give us the absolute truth, its shocking when something manages to fool that sense.
  • by Joe Random (777564) on Friday June 24, 2005 @07:27PM (#12905710)
    That's no moon!
  • Explained? RTFA? (Score:5, Insightful)

    by StaticLimit (26017) on Friday June 24, 2005 @07:30PM (#12905732) Homepage
    So the title of the submission is: Low-Hanging Moon Explained... and the text of the submission itself says "There is still no agreed on explaination for why the moon appears bigger".

    Who writes these titles? Do they even read the submission, let alone the article... (extra scorn if the submitter wrote the title)

    Wacky. And I read the article too (before it got posted here). There's definitely no explanation... a couple theories, sure, but they debunk the theories right in the article.

    - StaticLimit
    • Who writes these titles? Do they even read the submission, let alone the article... (extra scorn if the submitter wrote the title)

      Idiots do. See also today's "SPF (anti-spam system) is approved by IETF". It is neither aniti-spam, nor approved.

      You're not new here - you should know that!
  • by mcSey921 (230169) <mcseyNO@SPAMyahoo.com> on Friday June 24, 2005 @07:30PM (#12905739) Homepage Journal
    The moon, like a testicle, hangs low in the night sky.

    There goes the karma.
    • I thought it was my botany prof who first said it one night while were were staggering home after a hops lab.
  • by HighOrbit (631451) on Friday June 24, 2005 @07:33PM (#12905768)
    Perhaps when it is closer to the horizon, your line-of-sight to the moon also follows closer to the surface of the Earth. Because the atmosphere is denser at the surface, the denser atmophere has a greater lens effect?

    No? Well, it was just a shot-from-the-hip thought.
    • Because the atmosphere is denser at the surface, the denser atmophere has a greater lens effect?

      Nope, if you take a picture of the "large" moon at the horizon, and then take a picture of the "small" moon directly overhead with the same settings, they're exactly the same size on the image/photo.

  • Explained? (Score:3, Interesting)

    by RedWizzard (192002) on Friday June 24, 2005 @07:36PM (#12905788)
    I read TFA and didn't see any explanation. They described the two leading theories, but no conclusion was drawn. The end of TFA leaves it wide open: "For the moment at least, the real reason for the Moon Illusion remains up in the air. "

    I'd really like to see a bit more attention paid to making Slashdot headlines accurate, both by submitters and editors.

  • by DoorFrame (22108) on Friday June 24, 2005 @07:36PM (#12905789) Homepage
    I thought the moon appeared larger while on the horizon because suddenly the moon appears to be right next to objects whose size we can comprehend. In the middle of a night sky, the mooon is just a circle of light in a giant black space, on the horizon the moon is much much larger than buildings we know to be enormous. Even if against nothing more than the horizon, it still seems bigger because at least it's next to SOMETHING.
  • Bah... (Score:5, Funny)

    by NeuroManson (214835) on Friday June 24, 2005 @07:36PM (#12905790) Homepage
    Everyone knows that cameras add an extra 200,000 tons.
  • The illusion extends to constellations as well. Take a look at a constellation when it is up high and it seems smaller than when it is near the horizon.
  • And the editors have no dates. So they see the phrase "Low-Hanging Moon" and it sort of eats their brains.
  • by itzdandy (183397)
    { -There is still no agreed on explaination for why -the moon appears bigger when it's on the horizon -than when it's high in the night sky." }

    first, i did not read every post so excuse this if it has been addressed.

    is the earth round? is the atmosphere also round? so if a nearly clear object is bent does it not act as a lense? so if the atmosphere is between the viewer and the moon, wouldn't it bend light the same as a lense? so now tilt the top of the lense towards the viewer just like the atmos
    • ..is complete crap? wtf?

      Well, you could read TFA where it says "Then there are those who scoff that this is an illusion at all. They, at least, can be proved wrong. Hold a coin up to a low-lying moon to and compare differences in size. Any difference will remain exactly the same, as one traces the trajectory of the moon through the night."

      It is not larger.

  • I love how many people say that the answer is obvious, but they don't agree with the other obvious answers that are listed.
  • The math (Score:4, Funny)

    by MindPrison (864299) on Friday June 24, 2005 @07:40PM (#12905829) Journal
    The more you drink...

    ...the bigger it will seem

    20 % alcohol = 20 Bigger moon 40 & alcohol = thats one BIG moon 90 & alcohol = the size of the moon is no longer a concern of yours. You're somewhere else.

  • A blond newlywed was enjoying her honeymoon by staring at the night sky from a Hawaiian mountaintop with her newly betrothed. At one point he asked her which is closer, Texas or the moon.

    She thought about it for a moment and then her eyes glittered with a knowing look.

    She glanced around dramatically and replied, "Duuuh! Do you *see* Texas?"

    -
    This joke is intended as humor, no offense to any blondes out there, real or implied.

    No blondes were harmed during the creation of this joke.
  • I live in a light polluted town (Aurora, IL) so I barely get to see anything besides an ominous orange glow in the sky at night.

    But these past few nights I've just been sitting out watching the moon for a few hours at a time, and it really is something to look at if you haven't done so already. I know late night is prime geek computing time, but go outside for 5 minutes and check it out.
  • by kevlar (13509) on Friday June 24, 2005 @07:48PM (#12905880)
    The Moon doesn't change sizes (that the human eye can ascertain at least) and it is not magnified by the atmosphere on the horizon. It is merely an optical illusion.

    When the Moon is close to the horizon your brain compares its size with terrestrial objects. When its at its zenith, the brain does not. We only perceive it as being larger on the horizon, when in fact our brains are just misjudging its size.

    NASA scientists don't know this? Bullshit alert!
  • Here's a simple test to convince most people that the moon is the same size near the horizon then it is in the middle of the sky.

    When the moon rises, extend your arm all the way, hold your thumb next to the moon and take an approximate measurement of the moon against your thumbnail. You just need an approximation.

    A few hours later, when the moon is higher in the sky, do the same thing.

    This seems to be enough to convince most people that the moon is about the same size.

    Of course, then you have to deal wi
  • by Kelson (129150) * on Friday June 24, 2005 @07:58PM (#12905950) Homepage Journal

    Not since June 1987 has the moon been this low in the sky

    Umm... how about twice a day, when it rises and sets?

    Who writes this crap?

    • They left out the key word:
      Not since June 1987 has the full moon been this low in the sky

      See this story [nasa.gov] for a bit more detail.
      • by eskwayrd (575069) on Friday June 24, 2005 @09:25PM (#12906434)
        They left out the key word:
        Not since June 1987 has the full moon been this low in the sky

        Actually, they are not saying "this low in the sky". They are saying "hangs lower in the sky".

        The difference is simple:
        When the Moon is full (or nearly full depending on how long you have to wait for the Earth to rotate it into view), it can appear right on the horizon for any viewer (excepting those whose horizons block the Moon entirely). This happens roughly monthly, not every 20 years.

        "Hangs lower in the sky" is referring to the arc that the Moon appears to travel as the Earth rotates. Since the summer solstice was a few days ago, the tilt of the Earth makes the Sun appear in its most northerly position. Consequently, the Moon appears in its most southerly position, and it appears to 'hang' lower in the sky than during winter months for viewers in the Northern hemisphere (this effect is reversed for Southern hemisphere viewers).

        When the Moon 'hangs' lower in the sky, the illusion lasts significantly longer because the Moon appears to be closer to the horizon for a much longer period. As a result, far more people notice the illusion, even those who don't normally watch the Moon on a regular basis.

        This is the lowest hanging full Moon in 20 years mostly due to the timing of the full Moon relative to the solstice.

        Note: there is some slight magnification of the Moon at the horizon due to observing it through much more atmosphere than when the Moon is overhead. However, this effect makes the Moon look very slightly taller. The illusion being discussed here typically makes the Moon appear to be wider on the horizon.

        Note: IANAA (I am not an astronomer), but I'm fighting the urge to sleep in order to become one!
        • by CheshireCatCO (185193) on Friday June 24, 2005 @11:11PM (#12906927) Homepage
          I am an astronomer... and you appear to be mostly right. Which of course means that I'm about to nitpick.

          First, "Consequently, the Moon appears in its most southerly position, and it appears to 'hang' lower in the sky than during winter months for viewers in the Northern hemisphere (this effect is reversed for Southern hemisphere viewers)."

          It's true that the seasons move the location of the ecliptic (the Sun's annual path across the sky) and thus the Moon at night is further south when the Sun is further north. However, there's another effect at play here: the Moon has an inclined orbit (relative to the ecliptic). So depending on where you are in that cycle (it's 17.5 years long, if I recall right), the Moon's position above or below the ecliptic adds to or subtracts from the ecliptics north-south changes.

          So it's not so much the timing relative to the solstice (the odds of the solstice being on a day with an effectively-full moon are at least about 1/9, after all), it's about the precession of the lunar nodes.

          Also, the Moon is squashed near the horizon, not stretched tall. I have a great photo of this somewhere, but I seem to have lost it in my last move.
  • by AaronStJ (182845)
    From the headline: "Low-Hanging Moon Explained"
    From the article: "Experts have yet to agree on either or, indeed, any explanation."

    So... which is it?
  • While it should be common knowledge (as it makes sense) I see many people staring at the moon here, closer to the equator.

    When it is round it's OK, but as soonas it is a C or a D it really faces in a different direction ....

    creeped me a little the first time I saq it :)

    bigger moon ?
    sorry it is DAMN rainy season here, I haven't seen the moon for days ... it is pouring now too and i'm on my bike ... wish i had a batman suit, or at least my surfing wetsuit :( friday night kinda stuck in the office fixing
  • by iradel (894910)
    The answer is that it is an optical illusion of your brain, the moon doesn't change.

    To test this, go outside at noon (when the sun is highest and 'smallest'), take a penny, close one eye, and hold the penny out towards the sun so that it perfectly blocks the sun. Note how far away the penny is from your eye.

    Now go out at sunset when the sun is low on the horizon and seems huge. Again take the penny and hold it out to where it perfectly blocks the sun. You will notice that you are holding the penny
  • No mystery, (Score:5, Funny)

    by Maljin Jolt (746064) on Friday June 24, 2005 @08:35PM (#12906178) Journal
    it's bug in Matrix. A 2D transform/rendering artefact. Ever noticed a simple static texture for moon, with a black circle occlusion blended, no animation at all?
  • When it's that low use a low powered telescope and find a place you can identify easily.

    Then wait a few hours until it's small again and if it's smaller you have your answer.

    Course the naked eye also tells you the same thing. There are visible features of the moon that are identifiable and they're huge when it's low. When it's higher up in the sky they are smaller.

    The answer is clear there is no mystery.

(1) Never draw what you can copy. (2) Never copy what you can trace. (3) Never trace what you can cut out and paste down.

Working...