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Low-Hanging Moon Explained
Posted by
Zonk
on Fri Jun 24, 2005 06:21 PM
from the watch-your-head dept.
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."
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Mr President, Dr. Evil is on the line... (Score:5, Funny)
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.
Obvious. (Score:3, Funny)
Actually... (Score:5, Interesting)
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.
Parent
Re:Actually... (Score:5, Informative)
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.
Parent
Re:Actually... (Score:5, Funny)
Hey you batard I jus ttried this and no wIc an't seewhatIm typing....
Parent
Re:Actually... (Score:4, Funny)
Iris: "Oh... tomhudson posted instructions on Slashdot that were crafted to get less intelligent people to look at the sun. You're smelling their smoking eye sockets".
Blanche: "Oh. I thought that's what was going on, but I wanted to be sure".
Sound FX: [audience laughter from I Love Lucy]
Parent
Re:Actually... (Score:4, Funny)
The other way to make the moon smaller is to turn around, bend over, and look at it between your legs.
Yes, it sounds like a prank but it's not. We actually studied this illusion as part of a course dealing with optics and perception in college.
Parent
Re:Actually... (Score:4, Funny)
Parent
Re:Actually... (Score:5, Funny)
I don't know much about this whole telescope thing your talking about but the magnifying glass is a great idea. Of course you have to make sure that it's in focus or you wont see the fascinating details involved with the flares. Make sure that you hold the magnifying glass at the correct position so that the focal point of the magnifying glass is directly on your cornea. And ignore the smell.
Parent
old news... (Score:5, Funny)
Re:old news... (Score:4, Funny)
Parent
Bruce Almighty flashback (Score:5, Insightful)
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.
Re:Bruce Almighty flashback (Score:4, Informative)
Parent
Internal representation of the sky. (Score:3, Informative)
Re:Bruce Almighty flashback (Score:5, Interesting)
Parent
Re:Bruce Almighty flashback (Score:4, Interesting)
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.
Parent
Re:Bruce Almighty flashback (Score:5, Interesting)
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.)
Parent
Re:Bruce Almighty flashback (Score:3, Insightful)
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)
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
Re:Bruce Almighty flashback (Score:3, Informative)
Re:Bruce Almighty flashback (Score:3, Interesting)
The moon is actually rarely in the scenery when the moon is in the picure.
Re:Bruce Almighty flashback (Score:5, Interesting)
-kaplanfx
Parent
Re:Bruce Almighty flashback (Score:3, Interesting)
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
Head standing optional (Score:3, Interesting)
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
Re:Bruce Almighty flashback (Score:3, Interesting)
Speaking of thumbnails, a really good trick for estimating distances if you can estimate object size:
Measure the width of your thumbnail. Measure the distance between your thumb and your eye (arm extended, hitchhiker). Divide the thumb-eye distance by the thumbnail width. You'll get a number around 30.
To e
I didn't think this was a big mystery. (Score:3, Informative)
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
you mean... (Score:5, Funny)
Parent
Re:I didn't think this was a big mystery. (Score:5, Funny)
That's no moon.
Parent
The moon has appeared larger? (Score:4, Funny)
That's some moon. (Score:2)
Re:That's some moon. (Score:4, Funny)
Any attack made by you against this post would be a useless gesture, no matter what technical data you have obtained. This post is now the ultimate power in the universe. I suggest we use it.
Parent
Easy Fix (Score:5, Funny)
Re:Easy Fix (Score:3, Funny)
Re:Easy Fix (Score:5, Interesting)
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.
Parent
Perception of distance and perspective (Score:3, Insightful)
Wait a minute.... (Score:5, Funny)
Explained? RTFA? (Score:5, Insightful)
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
As Robin Williams said: (Score:5, Funny)
There goes the karma.
Umm... maybe because a thicker atmosphere? (Score:5, Interesting)
No? Well, it was just a shot-from-the-hip thought.
Re:Umm... maybe because a thicker atmosphere? (Score:3, Funny)
When you hold the dime over your head, the thinner atmosphere (3 ft higher than your head) doesn't magnify it as much.
Now, while holding the dime directly above your head, and watching it carefully, release the dime. You will notice that the dime begins to appears very large as it drops into the thicker atmosphere. This phenomenon is much easier to observe if you use something larger - like, say, a brick
Explained? (Score:3, Interesting)
I'd really like to see a bit more attention paid to making Slashdot headlines accurate, both by submitters and editors.
Isn't it just because of the frame of reference? (Score:3, Interesting)
Bah... (Score:5, Funny)
The math (Score:4, Funny)
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.
This is no mystery, its an optical illusion. (Score:3, Informative)
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!
"Low-hanging" moon? (Score:5, Insightful)
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?
Re:"Low-hanging" moon? (Score:5, Interesting)
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!
Parent
Re:"Low-hanging" moon? (Score:4, Informative)
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.
Parent
No mystery, (Score:5, Funny)
Re:Lense Effect (Score:3, Informative)
1) Nobody with even a passing knowledge of science spells "lense" with an "e" at the end.
2) The gravitational field of the Earth does not produce a lens effect. A gravitational lens occurs when light from behind an object is focused by the entire circumference of the object:
whereas any "natural lens effect" by the Earth for Earth-dwellers would only bend the l