Starship Asterisk*

I have always assumed that the reason that the moon seems larger at the horizon has been to do with the relative size of the objects around it. For instance when the moon is at the horizon it is close to trees and mountain ridges which are relatively small while when it is higher in the sky it is surrounded by large expanses of sky so it seems a lot smaller.

http://apod.nasa.gov/apod/ap090616.html

Happy Birthday APOD

Many many happy returns of the day. I love to begin my day with APOD.

Cheers,
Smita

The photo does not represent the question very well. The Moon IS bigger near the horizon, such as a Moonrise at the beach. This is due to the amount of atmosphere the light must go through to reach our eyes, NOT whether there are objects nearby. In this photo, the Moon is already high in the sky, above a group of hills or mountains! Incidently, the Sun is also bigger near the horizon.

The photo actually represents the question very well. The moon (or sun) does not change angular size as rises. It is not larger on the horizon than when it is high in the sky. This is an illusion.

ChiefChuckalucky wrote:The photo does not represent the question very well. The Moon IS bigger near the horizon, such as a Moonrise at the beach. This is due to the amount of atmosphere the light must go through to reach our eyes, NOT whether there are objects nearby. In this photo, the Moon is already high in the sky, above a group of hills or mountains! Incidently, the Sun is also bigger near the horizon.

The Moon is not larger near the horizon. In fact, it is smaller. The first reason is mechanical: it is farther away. That alone is enough to make it nearly 2% smaller. The second reason is optical. Parallel to the horizon, the atmosphere has no effect. But perpendicular to the horizon atmospheric refraction compresses the size of the Moon. That's what gives it (or the Sun) a flattened appearance right on the horizon.

The sense that the Moon and Sun are larger on the horizon is an optical illusion, pure and simple.

A similar effect can be seen in any port city. Large ships pass through the harbour daily, and seen from a bridge or from down at the shore, they're big but not startlingly so. But walk back into the city a half-dozen blocks, along a street with a clear view to the harbour, and wait for one of those container ships to pass by the end of the street, slipping between the buildings. Suddenly the ship will seem HUGE, even though it is now farther away from you than when you were standing down at the harbour shore. It would be interesting to find a clear explanation of this phenomenon, in particular whether it is strictly in the mind or if there's some measurable optical effect occurring.

Rob

rstevenson wrote:A similar effect can be seen in any port city. Large ships pass through the harbour daily, and seen from a bridge or from down at the shore, they're big but not startlingly so. But walk back into the city a half-dozen blocks, along a street with a clear view to the harbour, and wait for one of those container ships to pass by the end of the street, slipping between the buildings. Suddenly the ship will seem HUGE, even though it is now farther away from you than when you were standing down at the harbour shore. It would be interesting to find a clear explanation of this phenomenon, in particular whether it is strictly in the mind or if there's some measurable optical effect occurring.

I always think of Afghanistan as being a small country because it is hemmed in on all sides by larger countries.

Afghanistan MUST certainly be smaller than Iraq which so clearly looms over it neighbors to the west.

Why is there a reflection of the moon on the water ONLY directly under the last position of the moon?

Why are the superimposed parts of moons not brighter than the rest of the surfaces?

When zooming in, why is there a shadow on each moon on the superimposed parts?

No one else smells photoshop here?

http://en.wikipedia.org/wiki/1999_%C4%B0zmit_earthquake wrote:
<<The 1999 İzmit earthquake was a 7.6 magnitude earthquake that struck northwestern Turkey on August 17, 1999, at about 3:01am local time. The event lasted for 37 seconds, killing around 17 thousand people and leaving approximately half a million people homeless. Izmit earthquake occurred along the western portion of the North Anatolian Fault Zone (NAFZ). The Anatolian Plate, which consists primarily of Turkey, is being pushed west about 2-2.5 cm (0.8-1.0 in) a year, as it is squeezed between the Eurasian Plate on the north, and both the African Plate and the Arabian Plate on the south.

Major earthquakes in Turkey result from slips along the NAFZ or the Eastern Anatolian Fault. The earthquake had a rupture length of 150 kilometers (93 miles) extending from the city of Düzce all the way into the Sea of Marmara along the Gulf of İzmit. Offsets along the rupture were as large as 5.7 meters (18.7 ft). The earthquake caused a tsunami in the Sea of Marmara that was about 3 meters high.>>

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http://en.wikipedia.org/wiki/Destiny#Destiny_and_Kismet wrote:
The word kismet derives from the Arabic word qismah, and entered the English language via the Turkish word kısmet, meaning either "the will of Allah" or "portion, lot or fate". In English, the word is synonymous with fate or destiny. The word is also part of mainstream Hindi and is spelled किस्मत and when written in English in the Indian sub-continent is spelled kismat.

thecynicalhead wrote:Why is there a reflection of the moon on the water ONLY directly under the last position of the moon?

Why are the superimposed parts of moons not brighter than the rest of the surfaces?

When zooming in, why is there a shadow on each moon on the superimposed parts?

No one else smells photoshop here?

APOD wrote:In the above time-lapse sequence of the Moon taken in 2007, with one exposure taken to bring up the foreground of Izmit Bay in Turkey.

Single frame, multiple exposures, the last one longer than the rest.

thecynicalhead wrote:Why is there a reflection of the moon on the water ONLY directly under the last position of the moon?

Why are the superimposed parts of moons not brighter than the rest of the surfaces?

When zooming in, why is there a shadow on each moon on the superimposed parts?

No one else smells photoshop here?

It's a composite image- a stack made from multiple shots using different exposure times. By its very definition it has been built using Photoshop or a similar tool. Where's the problem?

I like to look at a picture for it's overall effect it has on me; whether it is pleasing to me or not. this one is pleasing to me. whether of not it is photo chopped or not doesn't bother on this one.

Orin

bystander wrote:The photo actually represents the question very well. The moon (or sun) does not change angular size as rises.
It is not larger on the horizon than when it is high in the sky. This is an illusion.

It would have been better to actually present the illusion
and then allow us to measure for ourselves:



http://www.ophtasurf.com/en/illusionpage2.htm

Chris...

We are talking about the apparent size of the Moon at the horizon Vs. high in the sky. NOT whether the Moon is actually bigger. I grant you that we are slightly further away from the Moon when it is rising or setting than when it is straight overhead. About 4000 miles further away.

But that's not what we the photo was about!

The Moon in this photo is NOT close to the horizon. It also does not have the view of the Moon really high in the sky.

The atmosphere will distort the Moon or the Sun close to the horizon. The amount of distortion is due to the amount of atmospheric particles, such as moisture, smoke, smog, and/or temperature changes such as seen with the Moon and the ship in today's photo! Here, the Moon is much closer to the actual horizon than the Turkey photo, where it is above hills! And it is bigger because of the distortion near the horizon! Sometimes the distortion will not create a completely round Moon, and other times it will.

I have personally seen a sunrise where the Sun was at least double its size seen at noon.

A better multiple exposure photograph needs to be taken.

Chris Peterson wrote:Parallel to the horizon, the atmosphere has no effect. But perpendicular to the horizon atmospheric refraction compresses the size of the Moon. That's what gives it (or the Sun) a flattened appearance right on the horizon.

In the APOD for 2009 June 20, I measured the flattened moon. It was about 107 pixels wide and about 92 pixels high (about 304 x 261 in the large image). Not surprisingly, this supports what you say.

ChiefChuckalucky wrote:We are talking about the apparent size of the Moon at the horizon Vs. high in the sky. NOT whether the Moon is actually bigger.

Well, then you need to say it that way. Because what you did say, explicitly, was that the Moon is bigger near the horizon. And that is not true. There is an illusion that it is larger- an illusion that not all people see the same.

The Moon in this photo is NOT close to the horizon. It also does not have the view of the Moon really high in the sky.

Certainly, this photo is not the best possible for discussing the Moon illusion. But I don't think that's the only thing this photo was about, either.

The atmosphere will distort the Moon or the Sun close to the horizon. The amount of distortion is due to the amount of atmospheric particles, such as moisture, smoke, smog, and/or temperature changes such as seen with the Moon and the ship in today's photo!

The distortion is due to refraction, caused by different densities in the air. It doesn't have anything to do with particles, moisture, smoke, or smog.

Here, the Moon is much closer to the actual horizon than the Turkey photo, where it is above hills! And it is bigger because of the distortion near the horizon!

This is a single image of the Moon, taken with a telephoto and foreground objects. You can't make any assessment of its apparent size to a viewer on the scene at all. This is a photographic illusion, and is unrelated to the conventional visual Moon illusion. In any case, atmospheric distortion can only make the Moon smaller, not larger.

I have personally seen a sunrise where the Sun was at least double its size seen at noon.

Well, there you go again. I assume what you mean to say is that you have seen a sunrise where the Sun appeared to you to be at least twice the size that it appeared to you at noon. Somebody else might see it very differently, because it is just an illusion. If you actually measured the size (which is easy), the Sun at sunrise will be a little smaller than at noon, because of its greater distance (this effect is tiny for the Sun, but quite significant for the Moon). It many also be a little smaller because of atmospheric distortion- that's a little more complicated visually because its effect is to change the shape, not just the size.

A better multiple exposure photograph needs to be taken.

I've seen such images, possibly even on APOD.

Maybe this APoD will illustrate the illusory nature of the effect a bit better.

Qev wrote:Maybe this APoD will illustrate the illusory nature of the effect a bit better.

So the moon doesn't get REALLY BIG until it has risen about the clouds, then.

Here is an easy way to personally determine the illusion that works fairly well:
At moonrise, when the moon appears visually larger to you, stick up your thumb at arms length and hold it up to the moon. Remark the relative size of your thumb to the size of the moon. It is likely only slight larger than 1/2 the width of your thumbnail. Now, make the same comparison a couple hours later (or once you feel the moon is visually smaller in the sky) and you will see that it is still the same apparent size (smaller than your thumbnail)

Well, there you go again. I assume what you mean to say is that you have seen a sunrise where the Sun appeared to you to be at least twice the size that it appeared to you at noon. Somebody else might see it very differently, because it is just an illusion.

Yes, Chris. It appeared to be twice the size (at least) than it appeared at noon. There were several hundred of us and we all agreed. We were at Air Force Basic Training at Lackland AFB in 1961. And from the way you keep using the word illusion, I guess everything we see is illusion. But there was no "very differently" about it. That Sun was HUGE!

Here is an easy way to personally determine the illusion that works fairly well:
At moonrise, when the moon appears visually larger to you, stick up your thumb at arms length and hold it up to the moon. Remark the relative size of your thumb to the size of the moon. It is likely only slight larger than 1/2 the width of your thumbnail. Now, make the same comparison a couple hours later (or once you feel the moon is visually smaller in the sky) and you will see that it is still the same apparent size (smaller than your thumbnail)

Good idea. I'll do that and report my findings. Might take a little while, but I'll try it!

ChiefChuckalucky wrote:And from the way you keep using the word illusion, I guess everything we see is illusion.

Everything we see passes through some kind of perceptual filter, but that doesn't mean everything is an illusion. That term is generally reserved for unexpected observations. We commonly perceive the Moon near the horizon as larger than overhead, even though it is not. So that's an illusion- a trick of some kind that our brain is playing on us. Compare that to viewing a person standing 20 feet away and one standing 100 feet away. Our vision quite correctly records a substantial difference between the sizes of the two. But our brain uses other information to "fix" the raw data, and we see the two people as being the same size. Nothing unexpected, so we don't call that an illusion.

Chris Peterson wrote:Everything we see passes through some kind of perceptual filter, but that doesn't mean everything is an illusion. That term is generally reserved for unexpected observations. We commonly perceive the Moon near the horizon as larger than overhead, even though it is not. So that's an illusion- a trick of some kind that our brain is playing on us. Compare that to viewing a person standing 20 feet away and one standing 100 feet away. Our vision quite correctly records a substantial difference between the sizes of the two. But our brain uses other information to "fix" the raw data, and we see the two people as being the same size. Nothing unexpected, so we don't call that an illusion.

I, for one, have never seen the "moon illusion". When I was young(er), my parents pointed out to me how the full moon was orange when it rose and became yellow and then white. I enjoyed looking at this phenomenon time after time after time, so I observed the full moon close to the horizon quite a lot, and not once did I get the impression that the moon was unusually large.

Harry Warren & Jack Brooks wrote:When the moon hits your eye like a big pizza pie, that's amore

And Dean Martin wasn't singing about Io.

apodman wrote:I, for one, have never seen the "moon illusion". When I was young(er), my parents pointed out to me how the full moon was orange when it rose and became yellow and then white. I enjoyed looking at this phenomenon time after time after time, so I observed the full moon close to the horizon quite a lot, and not once did I get the impression that the moon was unusually large.

I really do think that we all have an instinctive capability for
picking out the largest or smallest individual within a given group.

If you're a predator you want to zero in on the smallest (and presumeably weakest) member.

If you're a female you want to zero in on the alpha (and presumeably the largest) male.

When I brought home a female cocker spaniel puppy for my kids years ago
all she was interested in was attaching herself to me & barking at other large men.


A moon high in the vast sky or even rising over a large featureless salt flat probably looks pretty small.

But a moon rising over Lackland AFB is going to look pretty big
next to distant towers & buildings.
http://antwrp.gsfc.nasa.gov/apod/ap090128.html

apodman wrote:

Harry Warren & Jack Brooks wrote:When the moon hits your eye like a big pizza pie, that's amore

And Dean Martin wasn't singing about Io.

Ma n'atu sole,
cchiù bello, oje ne'
'O sole m-Io
sta 'nfronte a te!
'O sole, 'o sole m-Io
sta 'nfronte a te!
sta 'nfronte a te!

But another sun,
that's brighter still
It's my own sun
that's upon your face!
The sun, my own sun
It's upon your face!
It's upon your face!