Lunar eclipse 'magnified' in US...but why?

Trine

http://news.bbc.co.uk/2/hi/science_and_environment/10414201.stm

A partial lunar eclipse taking place on 26 June will appear magnified in the US by an effect known as the "moon illusion".

The eclipse will begin 10:17 GMT when the Moon enters the shadow of Earth.

Because of the timing, it will not be visible from the UK or Europe.

But in many parts of the US and Canada, the eclipse will appear larger because it occurs while the Moon is so close to the horizon.

According to Nasa, low-hanging Moons look "unnaturally large when they beam through trees, buildings and other foreground objects". The reason for this is not understood.

At its maximum, 54% of the Moon's diameter will be covered. This will occur at 0438 US pacific time (1138 GMT) - the event will last almost three hours.

Because the Moon, Sun and Earth are not aligned, it will not reach "totality".

I don't understand the part in bold. How is it not understood? I'm sure it's not simple and I sure can't explain it! But still, it struck me as something that would have been explained a long time ago. Just surprised me a little.

iceage

I always believed it to be an optical illusion.

EL_Loco

diffraction through atmosphere? curve of the earth? the moon actually only being a projection ala the truman show?!?!

dbran

Hi

The size of the moon when measured properly is virtually the same whether it is high in the sky or low down at the horizon. However to the human eye the moon when it is low down seems spectacularly large.

This is thought to be an optical illusion whereby the human brain is hard wired to judge the size and distance to any object it sees in terms of other objects it sees in the foreground that it already knows the distance to.

When the moon is high up in the sky there are no foreground objects for the brain to use as a reference and therefore the moon appears small as the brain has no way of telling if the moon is near or far away. When the moon is on the horizon it has lots more things to use to judge distance and as a result it appears large to us even though if you measure it, it is exactly the same size.

Hope this helps.


dbran

lord lucan

I've always figured it was an optical illusion. I remember coming home from work one night a couple of years ago and i had to pull the motorbike off the road. The Moon appeared to be sitting at the end of the road and was huge. It was so distracting i nearly had an accident. I just sat there for 20 minutes gazing at it,amazing sight.:)

I always thought it was just a funny point in its orbit
It's awesome when you see it all massive, low down and yellow.

Pittens

dbran wrote: »

Hi

The size of the moon when measured properly is virtually the same whether it is high in the sky or low down at the horizon. However to the human eye the moon when it is low down seems spectacularly large.

This is thought to be an optical illusion whereby the human brain is hard wired to judge the size and distance to any object it sees in terms of other objects it sees in the foreground that it already knows the distance to.

When the moon is high up in the sky there are no foreground objects for the brain to use as a reference and therefore the moon appears small as the brain has no way of telling if the moon is near or far away. When the moon is on the horizon it has lots more things to use to judge distance and as a result it appears large to us even though if you measure it, it is exactly the same size.

Hope this helps.


dbran

+1

I think thats the reason alright. I dont fully understand why this is not "understood" ( as in the original artice)

Anybody got any ideas?

EDIt:

I suppose the question is this: Do we subconsciously assume the sky is a dome at a certain distance from us?

Paradoxically the closer this virtual dome( we imagine) is the smaller the moon would appear to us, the further it is the bigger the moon would appear.

gbee

The moon illusion is a phenomenon where people are tricked into seeing the moon bigger low to the horizon because we are expecting to see the object this size!

If you take a picture of the moon with a standard lens you won't see the moon illusion.

If you are in orbit or in a high flying plane, you won't see the moon illusion.

If you are one of the few unaffected, you won't see the moon illusion.

I don't buy the mind being tricked thing, at that rate lots of other items, like ships about to come over the horizon, planes at the horizon and a few others should all display the 'moon illusion' but don't.

Trine

bluewolf wrote: »

I always thought it was just a funny point in its orbit

That's what I always thought, without really thinking about it. But obviously it doesn't make much sense if you do!

I think dbran's explanation makes the most amount of sense, but the BBC (and NASA?) reporting it as unexplained is interesting.

slade_x

Trine wrote: »

http://news.bbc.co.uk/2/hi/science_and_environment/10414201.stm



I don't understand the part in bold. How is it not understood? I'm sure it's not simple and I sure can't explain it! But still, it struck me as something that would have been explained a long time ago. Just surprised me a little.

Because ultimately the conclusion lies with completely understanding the brain and how it gives us our spacial perception.

Why when you see a cow or a horse almost stationary in a distant field do you immediately know its really, really far away. logic plays a very important role but also does the environment around it and what we conclude its apparent distance to be.

Is it the horizon and/ or relative objects in our view making the moon appear bigger than it really is, since we know the moon is really large and distance our brain may be perceiving it larger because we exaggerate the distance, as to compare it with relatively closer objects which we know are much much smaller but appear much bigger in comparison to what we imagine the true size of the moons is and the distance for both.

or could it even be, is it the lack of a reference object or horizon that makes the moon appear smaller than it really is approaching the zenith because we think its closer.

Do we think the moon should take up more space in the sky because we perceive it as much more distant as we know its very very far away but also much larger in comparison to our typical view of the horizon and its proximity ( etc. buildings, trees and more distant buildings and trees in perspective)

i think currently its more of a psychological view at this point. i think its the latter. our brains might just be making it bigger than it is at the horizon

r0n0c

might it have anything to do with the fact that when the moon is low on the horizion we're looking at it through more of the atmosphere than normal and the air and moisture in the atmosphere have a greater magnifying effect?

slade_x

r0n0c wrote: »

might it have anything to do with the fact that when the moon is low on the horizion we're looking at it through more of the atmosphere than normal and the air and moisture in the atmosphere have a greater magnifying effect?

The atmosphere wont gather and focus light for our eyes, it does affect the transmission and scattering of light however.

stevoslice

just read an interesting article on it recently, liking it to the ponzo illusion.
On my phone so can't upload an image, but if you go to the bad astronomy website and search for ponzo you should find it.

FISMA

As most have already stated, when viewed on the Horizon the moon will look HUGE! However, when overhead it looks tiny. If you ever have the opportunity to see the moon just rising over a city, you'll be amazed at how big it looks.

If you made a crude measurement, like diameter marked off on a card arm's length away, when the moon is low vs high, the measurements will be virtually the same.

However, it should be noted that moon will indeed be "squashed" a bit when low on the horizon due to refraction. A bit tough to perceive over the course of one night.