Low-Hanging Moon Explained

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."

Comments

Mr President, Dr. Evil is on the line...

[TripMaster Monkey]

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.

[Anonymous Coward]

Duh! Because it's closer!

old news...

[deft]

some guy who got gods powers is trying to get laid... apparently its taking longer than the last guy i saw try this one.

Re:old news...

[AstrumPreliator]

Why did you rate this guy Offtopic? I mean come on, Bruce Almighty wasn't that bad. =P

Bruce Almighty flashback

[JWSmythe]

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.

Re:Bruce Almighty flashback

[Laivincolmo]

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.

Re:Bruce Almighty flashback

[toddbu]

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.

Re:Bruce Almighty flashback

[nofx_3]

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 was the first hit on google. I recommend trying the full tour, its neat stuff.

-kaplanfx

Re:Bruce Almighty flashback

[ahecht]

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.

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.

Re:Bruce Almighty flashback

[Fittysix]

Photographers actually use a trick to capture the big moon: they zoom in on the moon alone in the sky, then use a double exposure to capture the scenery
The moon is actually rarely in the scenery when the moon is in the picure.

Re:Bruce Almighty flashback

[DavidTC]

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.)

The moon has appeared larger?

[Anonymous Coward]

For the past few nights the moon has appeared larger? Could this open some eyes and increase interest in alternative (Linux, Mac) offerings?

Easy Fix

[Laivincolmo]

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

[Lattitude]

When you're in that position, it's important to look at the correct moon...

Re:Easy Fix

[Council]

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 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.

Wait a minute....

[Joe Random]

That's no moon!

you mean...

[circletimessquare]

if you moon the moon there will be more moon?

Explained? RTFA?

[StaticLimit]

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

As Robin Williams said:

[mcSey921]

The moon, like a testicle, hangs low in the night sky.

There goes the karma.

Umm... maybe because a thicker atmosphere?

[HighOrbit]

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.

Re:Umm... maybe because a thicker atmosphere?

[nytes]

That's only because the thicker atmosphere also magnifies the dime when it's held low to the horizon.

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.

Internal representation of the sky.

[Joe Random]

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").

Actually...

[objekt]

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.

Re:Actually...

[tomhudson]

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.

Re:Actually...

[gardyloo]

Also works with the sun, etc.

Hey you batard I jus ttried this and no wIc an't seewhatIm typing....

Re:Actually...

[eno2001]

Blanche: "Eww! Iris, what's the smell"?
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]

Re:Actually...

[Bad D.N.A.]

"And if you look at the sun with a telescope or magnifying glass, you can actually see solar flares."

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.

Re:Actually...

[Call Me Black Cloud]

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.

Re:Actually...

[tomhudson]

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.

Damn, I had forgotten about that one. Guess its because it inevitably leads to viewing another type of "low-hanging moon" sighting.

Bah...

[NeuroManson]

Everyone knows that cameras add an extra 200,000 tons.

Re:I didn't think this was a big mystery.

[clem]

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

That's no moon.

The math

[MindPrison]

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.

Re:That's some moon.

[mugnyte]

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.

"Low-hanging" moon?

[Kelson]

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?

[eskwayrd]

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!

Re:"Low-hanging" moon?

[CheshireCatCO]

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.

No mystery,

[Maljin Jolt]

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?