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Moon illusion



 
 
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  #1  
Old March 24th 11, 01:15 AM posted to sci.physics,sci.physics.relativity,sci.astro
Rama
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Posts: 12
Default Moon illusion

1. It is said that moon illusion is psychological perception, not
physical i.e it got nothing to do with atmospheric refraction.
2. The horizone full moon is at farther distance compared to overhead
moon. This variation in distance is physical.

So as moon illusion is psychological, it should work if earth itself
is removed. Now just observer(you) in space. Imagine one moon at
distance of 390,000 km straight before your eyes(horizone moon) and
second moon at distance of 384,000 km above (overhead moon).

As moon illusion is psychological, 'horizone moon' should look larger
than 'overhead moon'.

On same logic, any distant object in space should look larger than
closer object.

Please point out any mistake.

Thanks!
  #2  
Old March 24th 11, 01:34 AM posted to sci.physics,sci.physics.relativity,sci.astro
[email protected]
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Posts: 1,346
Default Moon illusion

In sci.physics Rama wrote:
1. It is said that moon illusion is psychological perception, not
physical i.e it got nothing to do with atmospheric refraction.
2. The horizone full moon is at farther distance compared to overhead
moon. This variation in distance is physical.

So as moon illusion is psychological, it should work if earth itself
is removed. Now just observer(you) in space. Imagine one moon at
distance of 390,000 km straight before your eyes(horizone moon) and
second moon at distance of 384,000 km above (overhead moon).

As moon illusion is psychological, 'horizone moon' should look larger
than 'overhead moon'.

On same logic, any distant object in space should look larger than
closer object.

Please point out any mistake.


Not taking, or perhaps sleeping through, high school trigonometry.

The diameter of the moon is roughly 3,500 km.

The difference in the subtended angle at the two distances is about 0.008
degrees, below the resolution of the eye.


--
Jim Pennino

Remove .spam.sux to reply.
  #3  
Old March 24th 11, 01:40 AM posted to sci.physics,sci.physics.relativity,sci.astro
Androcles[_40_]
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Posts: 94
Default Moon illusion


"Rama" wrote in message
...
| 1. It is said that moon illusion is psychological perception, not
| physical i.e it got nothing to do with atmospheric refraction.
| 2. The horizone full moon is at farther distance compared to overhead
| moon. This variation in distance is physical.

By one Earth radius, and anyway the moon appears larger
near the horizon than overhead.
It should appear smaller, therefore the effect is psychological.
The reason it appears larger is the background, the effect is in
photographs, too.


| So as moon illusion is psychological, it should work if earth itself
| is removed. Now just observer(you) in space. Imagine one moon at
| distance of 390,000 km straight before your eyes(horizone moon) and
| second moon at distance of 384,000 km above (overhead moon).
|
| As moon illusion is psychological, 'horizone moon' should look larger
| than 'overhead moon'.
|
It does. shrug

| On same logic, any distant object in space should look larger than
| closer object.
|
| Please point out any mistake.
|
The moon only seems larger when compared to trees, houses, objects
that are on the ground. By looking through a tube to hide them the
effect goes away. Holding your thumb up (or a coin) at arms length
to obscure the moon will quickly show you the size is the same on the
horizon or overhead.



  #4  
Old March 24th 11, 02:16 AM posted to sci.physics,sci.physics.relativity,sci.astro
Sam Wormley[_2_]
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Posts: 3,966
Default Moon illusion

On 3/23/11 7:15 PM, Rama wrote:
1. It is said that moon illusion is psychological perception, not
physical i.e it got nothing to do with atmospheric refraction.
2. The horizone full moon is at farther distance compared to overhead
moon. This variation in distance is physical.



Background on Moon Illusion
http://en.wikipedia.org/wiki/Moon_illusion
  #5  
Old March 24th 11, 02:41 AM posted to sci.physics,sci.physics.relativity,sci.astro
pete[_2_]
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Posts: 17
Default Moon illusion

Rama wrote:

1. It is said that moon illusion is psychological perception, not
physical i.e it got nothing to do with atmospheric refraction.
2. The horizone full moon is at farther distance compared to overhead
moon. This variation in distance is physical.

So as moon illusion is psychological, it should work if earth itself
is removed.


No.

The illusion is caused by the proximity to the horizon.

--
pete
  #6  
Old March 24th 11, 02:42 AM posted to sci.physics,sci.physics.relativity,sci.astro
Tom Roberts
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Posts: 344
Default Moon illusion

Rama wrote:
[...]


The illusion that the moon is larger when near the horizon than when overhead is
due to humans applying their general expectation about the size of objects in
the sky to a situation in which those expectations are wrong. Birds of a given
size look smaller near the horizon than when overhead, simply because they are
farther away; since the moon appears the same size in both locations [#], we
INTERPRET this as it being bigger near the horizon.

[#] Instruments that measure its angular spread show unambiguously
that the image of the moon has the same angular spread in any given
night.


Tom Roberts
  #7  
Old March 24th 11, 06:09 AM posted to sci.physics,sci.physics.relativity,sci.astro
palsing[_2_]
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Posts: 3,068
Default Moon illusion

On Mar 23, 5:15*pm, Rama wrote:
1. It is said that moon illusion is psychological perception, not
physical i.e it got nothing to do with atmospheric refraction.
2. The horizone full moon is at farther distance compared to overhead
moon. This variation in distance is physical.

So as moon illusion is psychological, it should work if earth itself
is removed. Now just observer(you) in space. Imagine one moon at
distance of 390,000 km straight before your eyes(horizone moon) and
second moon at distance of 384,000 km above (overhead moon).

As moon illusion is psychological, 'horizone moon' should look larger
than 'overhead moon'.

On same logic, any distant object in space should look larger than
closer object.

Please point out any mistake.

Thanks!


The moon illusion works for more than just the moon, it works for
entire constellations. Orion rising or setting is huge, but it appears
to be much smaller (to my eye) when it is culminating, and the same
can be said for other constellations that get high enough in the
sky... in other words, Grus doesn't change apparent size at all for
me.

\Paul A
  #8  
Old March 24th 11, 09:00 AM posted to sci.physics,sci.physics.relativity,sci.astro
Mike Dworetsky
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Posts: 715
Default Moon illusion

pete wrote:
Rama wrote:

1. It is said that moon illusion is psychological perception, not
physical i.e it got nothing to do with atmospheric refraction.
2. The horizone full moon is at farther distance compared to overhead
moon. This variation in distance is physical.

So as moon illusion is psychological, it should work if earth itself
is removed.


No.

The illusion is caused by the proximity to the horizon.


But that is still a psychological effect, Sam. To get the Moon illusion,
you need to be on a planet (Earth) so that you have a horizon* and an
illusion (probably something "hard-wired" in the visual system) that the
Moon looks larger on the horizon than higher in the sky.

*Question (that may never have been asked but should be tested): Do
astronauts on the ISS have an impression that the full Moon is larger when
seen "rising" or "setting" than at other times? They are in free-fall
(zero-g) but Earth gives them a horizon of sorts.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

  #9  
Old March 24th 11, 12:06 PM posted to sci.physics,sci.physics.relativity,sci.astro
Rama
external usenet poster
 
Posts: 12
Default Moon illusion



Mike Dworetsky wrote:
pete wrote:
Rama wrote:

1. It is said that moon illusion is psychological perception, not
physical i.e it got nothing to do with atmospheric refraction.
2. The horizone full moon is at farther distance compared to overhead
moon. This variation in distance is physical.

So as moon illusion is psychological, it should work if earth itself
is removed.


No.

The illusion is caused by the proximity to the horizon.


But that is still a psychological effect, Sam. To get the Moon illusion,
you need to be on a planet (Earth) so that you have a horizon* and an
illusion (probably something "hard-wired" in the visual system) that the
Moon looks larger on the horizon than higher in the sky.

*Question (that may never have been asked but should be tested): Do
astronauts on the ISS have an impression that the full Moon is larger when
seen "rising" or "setting" than at other times? They are in free-fall
(zero-g) but Earth gives them a horizon of sorts.


Some people had asked this question to Astronaut Paolo in ISS. He
replied to ESA and europeanspaceagency posted his reply on this page.
Please scroll for 'europeanspaceagency'
http://flickr.com/photos/magisstra/5372739290/

His answer is not clear. He said that he has not done 'experiment' and
kept talking about squashed moon. Further follow-up was futile.
  #10  
Old March 24th 11, 12:50 PM posted to sci.physics,sci.physics.relativity,sci.astro
Rama
external usenet poster
 
Posts: 12
Default Moon illusion



palsing wrote:
On Mar 23, 5:15*pm, Rama wrote:
1. It is said that moon illusion is psychological perception, not
physical i.e it got nothing to do with atmospheric refraction.
2. The horizone full moon is at farther distance compared to overhead
moon. This variation in distance is physical.

So as moon illusion is psychological, it should work if earth itself
is removed. Now just observer(you) in space. Imagine one moon at
distance of 390,000 km straight before your eyes(horizone moon) and
second moon at distance of 384,000 km above (overhead moon).

As moon illusion is psychological, 'horizone moon' should look larger
than 'overhead moon'.

On same logic, any distant object in space should look larger than
closer object.

Please point out any mistake.

Thanks!


The moon illusion works for more than just the moon, it works for
entire constellations. Orion rising or setting is huge, but it appears
to be much smaller (to my eye) when it is culminating, and the same
can be said for other constellations that get high enough in the
sky... in other words, Grus doesn't change apparent size at all for
me.


Doesn't it mean that sky (space) at horizone is magnified like coin in
water is magnified? Reason may be anything, most probably atmospheric
refraction.
 




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