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Poll: The moon is about the same size as one of the following held at arms length
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The moon is about the same size as one of the following held at arms length

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  #21  
Old 27-02-2008, 06:15 PM
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spearo (Frank)
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Well,
I immediately thought "cherry", then read the posts and voted cherry.
Now I just need to find a cherry that matches the size of the Moon at arm's length.
frank
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  #22  
Old 27-02-2008, 06:34 PM
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Definately the pea. You can cover the full moon with the tip of your little finger held at arms length. Mind you you have to close one eye
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  #23  
Old 27-02-2008, 07:21 PM
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I voted for a pea.

Al.
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  #24  
Old 27-02-2008, 07:23 PM
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The Moon takes up half of a degree of the sky, the same as the Sun and can be covered by your little finger held at a normal persons arms length, so you don't have to wait fo a Full Moon to check.
But don't stare at the Sun with unaided eyes for to long
Ron
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  #25  
Old 27-02-2008, 07:27 PM
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Although I did vote about cherry size, it is still to bloody big when you want to image.

Leon
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  #26  
Old 27-02-2008, 07:48 PM
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Originally Posted by leon View Post
Although I did vote about cherry size, it is still to bloody big when you want to image.

Leon
LOL too right!
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  #27  
Old 27-02-2008, 09:26 PM
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But don't stare at the Sun with unaided eyes for to long
Ron
Bugga! NOW you tell me ...


frank
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  #28  
Old 27-02-2008, 09:32 PM
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Well, no one has come up with any maths to justify their thoughts/guesses/beliefs, so;

The distance from my eye to my fingers "holding a pea" is 710mm
The pea is 8mm, so the angle subtended is 0.65 degree

The cherry is 18mm, so the angle subtended is 1.45 degrees

The moon tonight is 399715 km away, and its diameter is 3474km, so the angle is 0.5 degree. (Starry Night)

So if you are holding a small pea, that's the answer, approximately.

I guessed at the cherry, so I was wrong, as are 52% of the guesses, but a cherry stone would be nearer the mark.
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  #29  
Old 27-02-2008, 10:25 PM
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I did a kneejerk "cherry" and immediately knew I was wrong. Since I started this hobby, I've always held up my little finger at arms length to the full moon and can always more than block it out. And the tip of my little finger is no cherry

The brain is a strange thing. Hold your little finger up now at arms length and think whether the tip of that finger would cover the full moon. "No way", your brain says, "the Moon is much larger than that!" Well, we can all try it in three weeks time.
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  #30  
Old 27-02-2008, 11:20 PM
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I voted 'Pea'.
Ya'sawll knows thats the moons izonly 1/2 degree/30 AM.
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  #31  
Old 28-02-2008, 02:48 AM
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I voted cherry because I like red more than orange, green, silver, or undefined.
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  #32  
Old 29-02-2008, 12:06 AM
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There are a lot of people who like their cherries on this forum
Ron
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  #33  
Old 29-02-2008, 02:19 AM
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Moon

I have read plenty of times how 'big' the moon appears in the sky, and reasons why.

One I have read, is that a full moon rising just above the horizon looks 'so big' because it is a psychological trick of the mind. That being because the moon is closer to objects on the horizon, the mind has some terrestrial objects to 'compare' it size too. And that is what makes the rising full moon 'look so big'. Personally I disagree with this psychological explanation, like I disagree with many things psychologists say are psychological 'facts'.

It was when I was a child that I became aware of a phenomenon of how light is transmitted through liquids. For example, using a ruler go and try and poke a fish in bowl of water, or a fish tank and you will see what I mean. Even better try going spear fishing flounder. The water, at an angle 'bends' the light, so if you are pointing your spear straight at the target, you are going hungry mate!

The next time I became aware of the transmission of light through water was also when I was a kid, when we used to go to a take away restaurant. They had a massive fish tank full of tropical fish. I noticed that if you looked through the end walls of that tank objects outside the other end of the tank appear much bigger / closer than if you put your head around the corner of that tank and looked at them through just air.

I also noticed this when I used to got snorkeling / spear fishing. Underwater objects appear 'much bigger' and closer than they actually are, and many a time I was disappointed to find that my spear never had the range, and when I did get a hit what I thought would feed a family of 10 underwater wasn't so great when landed back on dry land. Also when underwater, looking up through the surface, objects above the surface appear magnified.

Now, the atmosphere at mean sea level is 40 times denser than water. But the atmosphere acts like a liquid.

I have a hunch, based on my previous visual experiments with water / liquid, that a rising full moon 'appears' much bigger as it rises as the greater thickness of the atmosphere you are looking through as the moon rises above the horizon, is acting on the transmission of the light from the moon, just like is does when viewing objects through water in a fish tank, and underwater.

I have tested the 'psychological' explanation, and it just doesn't cut it.

I have made a point of being at the bottom of an extremely steep granite cliff, that was close to 2500 feet, and I have observed the moon 'rise' above the top of the cliff, through the trees, and a fire watch tower, and at that elevation it would be above the horizon, roughly 30 degress, it does not 'appear' to look the same 'big' size it does as it 'rises' above the horizon as if you were out on the plains watching it rise.

Well, that's what I think is the reason why.

In any event watching a full moon on the rise usually makes me stop for a few minutes to enjoy it.
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  #34  
Old 29-02-2008, 06:25 AM
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Pea.
Or about the size of your smallest fingernail.
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  #35  
Old 29-02-2008, 06:37 AM
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[quote=Night Owl;301931]
I have a hunch, based on my previous visual experiments with water / liquid, that a rising full moon 'appears' much bigger as it rises as the greater thickness of the atmosphere you are looking through as the moon rises above the horizon, is acting on the transmission of the light from the moon, just like is does when viewing objects through water in a fish tank, and underwater.

I have tested the 'psychological' explanation, and it just doesn't cut it.

I have made a point of being at the bottom of an extremely steep granite cliff, that was close to 2500 feet, and I have observed the moon 'rise' above the top of the cliff, through the trees, and a fire watch tower, and at that elevation it would be above the horizon, roughly 30 degress, it does not 'appear' to look the same 'big' size it does as it 'rises' above the horizon as if you were out on the plains watching it rise.

quote]

I have no way to measure wether there is an actual size difference due to atmospheric distortion close to the horizon. It would be great if someone out there could do the experiment.

I Disagree with the lack of size illusion at higher elevations though. I find that there is little difference compared to looking at the moon rising over a mountain peek or distant tree line. I have done the "hold little fingertip out at arms length" experiment at different moon elevations (very scientific ) and found the same effect: it does look bigger.
Well, thats just my thoughts.
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  #36  
Old 29-02-2008, 06:40 AM
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OMG.
Somebody said Dinner Plate.
Now thats psychology.
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  #37  
Old 29-02-2008, 07:16 AM
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1/2 a Degree (if I remember correctly !) so I went with a Pea
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  #38  
Old 29-02-2008, 09:16 AM
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Quote:
Originally Posted by Sharnbrook View Post
Well, no one has come up with any maths to justify their thoughts/guesses/beliefs, so;

The distance from my eye to my fingers "holding a pea" is 710mm
The pea is 8mm, so the angle subtended is 0.65 degree

The cherry is 18mm, so the angle subtended is 1.45 degrees

The moon tonight is 399715 km away, and its diameter is 3474km, so the angle is 0.5 degree. (Starry Night)

So if you are holding a small pea, that's the answer, approximately.

I guessed at the cherry, so I was wrong, as are 52% of the guesses, but a cherry stone would be nearer the mark.
Yep, that's right. I was thinking pea at 6mm, held 60 cm away. The angle is 0.573 degrees, or 34'. Since the average size of the moon is 31', the pea is about right. Really unbelievable!
Geoff
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  #39  
Old 01-03-2008, 02:50 AM
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Quote:
Originally Posted by [1ponders] View Post
Definately the pea. You can cover the full moon with the tip of your little finger held at arms length. Mind you you have to close one eye
Absolutely Agree.

I can Block a Full Moon with the tip,of my little finger ,held at arms length.

I voted "Pea" also.

John
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  #40  
Old 01-03-2008, 05:09 PM
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Now, the atmosphere at mean sea level is 40 times denser than water
The density of water is 1 gram per cc, or 1 kg per litre, or 1 tonne per cubic meter. The weight of 1 cubic meter of dry air at sea level, at 15 deg C, is approximately 1.226 kg, or less than 1/800th the density of water.

The atmospheric pressure at sea level is approximately 101 kPa, but pressure is not the same as density. The weight of a column of "atmosphere" with a base area of 1 square centimeter is approximately 1 kg, but I'm not sure what you mean by atmosphere is 40 times denser than water?

I can recall my physics master at school, sometime in the late 1950s, explaining that the moon looked bigger at moonrise because of the refraction of the denser air at just a few degrees of elevation, whereas when the moon is overhead, the light is striking the atmosphere at 90 degrees, and therefore there is no (or minimal) diffraction. However, I have heard that if you photograph the moon at moonrsie, or at its zenith, the size of the image is identical. That's another project to be undertaken sometime...........
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