Why the moon looks bigger at the horizon

[PhanthomJay]

Yes, when I said about the size of the sun, I was comparing it to what I thought was the size of the sun when I last viewed it during a sunset through a layer of clouds, some years ago. So you are correct, I can't compare the size of the moon with the size of something I saw years ago. I was really comparing it to the bright sun shining fully, which I can only look at with a glancing eye. So I'll correct my statement : The harvest moon last year appeared greater than the size of the sun. I can't believe that no one else on this forum has ever viewed the Harvest Moon at moonrise over the horizon. IT IS HUGE. Next week when I view it, I'll eat crow if I'm wrong. Of course, i won't be able to prove it appeared huge, so I guess you should look yourself and give me your take on it.

 

[john.phillip]

On the Southern Hemisphere, the Harvest Moon was on March. How could you see the moon larger on the Northern Hemisphere, on August, while it had a normal size for viewers on the South, and vice-versa on March ?

http://www.archimedes-lab.org/atelier.html?http://www.archimedes-lab.org/moon_illusion/moon.html

 

[Janus]

Nice! Did you use a commercial package? Which one?

I thought of a suggestive comeback to this, but we forum moderators need to set a good example.

I used POV-Ray.

 

[DaveC426913]

The harvest moon last year appeared greater than the size of the sun. I can't believe that no one else on this forum has ever viewed the Harvest Moon at moonrise over the horizon. IT IS HUGE.

No one is arguing that you looked at the Moon and saw it was huge. In fact, that is exactly what we're saying.

But without any objective measurement, who are you to claim that what you saw was not simply an illusion?

 

[DaveC426913]

On the Southern Hemisphere, the Harvest Moon was on March. How could you see the moon larger on the Northern Hemisphere, on August, while it had a normal size for viewers on the South, and vice-versa on March ?

I think you're missing his point.

He is claiming it's a phenomenon of atmosphere and viewing angle, which will be specific to one's location.

Not that it's right, but you're missing his argument.

 

[john.phillip]

He is claiming it's a phenomenon of atmosphere and viewing angle, which will be specific to one's location.

I reviewed PhanthomJay posts, and I think you are right.

 

[PhanthomJay]

No one is arguing that you looked at the Moon and saw it was huge. In fact, that is exactly what we're saying.

But without any objective measurement, who are you to claim that what you saw was not simply an illusion?

I am NOT claiming it wasn't an illusion. I am claiming that the Harvest Moon ,in particular, on the horizon , appeared , last year, to me (and my grandkids), subjectively, to be bigger than other full moons I've seen on the horizon, and I don't know why. Let me put it this way: When I viewed the full moon over the horizon , about 3 weeks ago I believe, it appeared, as one would expect, due to the moon illusion effect, larger than it appeared when directly overhead. I placed a dime at arms length in front of me (I wanted to use a pencil eraser, but I can never find one when I need it most), but anyway, the dime more than covered the moon. When I removed the dime and viewed it, it appeared big again, oh I don't know, maybe the size of a 10 inch cheese (or pepperoni) pizza. I think we all agree as to why. Now next week, when I view the rising Harvest Moon over the Horizon at sunset, I fully expect that holding a dime at arms length in front of me, (or perhaps even a pencil eraser that i'll bring with me), will also more than cover the moon. But when i remove that dime, the moon will appear bigger than a 10 inch pizza, oh, say, maybe the size of a 16 inch pizza fully loaded with all the toppings. I don't know why the illusion on this special night will be so big. It won't appear to be as big as say the frontal area of a Mack Truck, but it will be big for sure, and until i view it, I can't yet describe how big. Again, you should view it yourself, and give me your 'trustworthy' subjective take on how big you think is its apparent size. Mind you, I'm not skilled in astronomy and talking as a science advisor, but rather, as a layman who has seen an extra HUGE Harvest Moon. And I hope I don't strain my back when viewing it through my legs. I am really looking forward to this event. It'll probably be cloudy, but if not, I'll give you my honest take on it.

 

[DaveC426913]

I don't know why the illusion on this special night will be so big. It won't appear to be as big as say the frontal area of a Mack Truck, but it will be big for sure.

Oh I know why. The harvest moon is a full moon and a particularly bright moon because that particular full moon, of all the 13 in the year, it is directly opposite the sun AND right near the horizon. That is the whole thing about the harvest moon and why it is so spectacular.

But its disc does not subtend any larger angle of the sky.

 

[PhanthomJay]

Oh I know why. The harvest moon is a full moon and a particularly bright moon because that particular full moon, of all the 13 in the year, it is directly opposite the sun AND right near the horizon. That is the whole thing about the harvest moon and why it is so spectacular.

OK, I'll buy it.

But its disc does not subtend any larger angle of the sky.

Agreed

 

[JDługosz]

Oh I know why. The harvest moon is a full moon and a particularly bright moon because that particular full moon, of all the 13 in the year, it is directly opposite the sun AND right near the horizon. That is the whole thing about the harvest moon and why it is so spectacular.

Hmm, how is that different than any other full moon? That's what it means for it to be full. And it will be near the horizon at some point during the day.

 

[Buckleymanor]

OK, I'll buy it.Agreed

Oh I know why. The harvest moon is a full moon and a particularly bright moon because that particular full moon, of all the 13 in the year, it is directly opposite the sun AND right near the horizon. That is the whole thing about the harvest moon and why it is so spectacular.

But its disc does not subtend any larger angle of the sky.

Then there is the real reason

 

[PhanthomJay]

Then there is the real reason

Grazie molte!

 

[seto6]

doesnt it have to do with light bending? near Earth surface?

 

[DaveC426913]

doesnt it have to do with light bending? near Earth surface?

No. In fact, refraction near the horizon works to make the Moon look smaller.

Read the thread.

 

[wortzman]

I would think that the light bends through the same angle whether the moon is above or in the horizon. The difference is only that it travels much further, getting to your eye, when it is on the horizon.

 

[DaveC426913]

I would think that the light bends through the same angle whether the moon is above or in the horizon. The difference is only that it travels much further, getting to your eye, when it is on the horizon.

Refraction is a well-known phenomenon. If you look directly down into a swimming pool (like the Moon high overhead), you see no bending of light rays, but if you look at through it at an oblique angle (like the Moon near the horizon), you see a significant bending.

So, the phenom is real enough, it just doesn't have a significant effect here.

 

[PhanthomJay]

2 more days till the Harvest Moonrise over the horizon at the Equinox... I hope it looks like this:

 

[DaveC426913]

2 more days till the Harvest Moonrise over the horizon at the Equinox... I hope it looks like this:

Please tell me you're kidding around with that pic .

 

[PhanthomJay]

Please tell me you're kidding around with that pic .

Hey, you're the humorist around here...I'm dead serious.
By the way, I looked at the moon last night a bit after moonrise...the sun had not set yet, and the moon was about 5 degrees or so above the horizon, rather dim with the sunlight still glowing...it looked quite ordinary...and white...nothing special about it...but come this Thursday, or maybe Friday, when the moon rises a bit after sunset...well, we'll see, we'll see...

 

[DaveC426913]

Hey, you're the humorist around here...I'm dead serious.

Well, the reason I'm asking is you don't really think that the Moon literally appears that large...


The pic is clearly taken without proper context - it is taken with a telephoto lens. Telephoto lenses can dramatically enlarge foreground objects in relation to background objects.

 

[DaveC426913]

Hey, you're the humorist around here...I'm dead serious.
By the way, I looked at the moon last night a bit after moonrise...the sun had not set yet, and the moon was about 5 degrees or so above the horizon, rather dim with the sunlight still glowing...it looked quite ordinary...and white...nothing special about it...but come this Thursday, or maybe Friday, when the moon rises a bit after sunset...well, we'll see, we'll see...

What you need to do is take a picture tonight, with some skyline object as refernce, then take the same pic again tomorrow night.

 

[PhanthomJay]

Big enough for you? I know its a telephoto, but As I remember the harvest moon last year, it almost did appear that big...in a day or 2, I'll know for sure...

 

[cjl]

Telephotos make it appear bigger than it actually is. What you really need to do is take a picture of it in a day or two with a known lens and camera from a known position. Then, a couple of weeks (or a month) later, take another picture with the same lens and camera. That'll show that there's effectively no difference.

 

[PhanthomJay]

Telephotos make it appear bigger than it actually is. What you really need to do is take a picture of it in a day or two with a known lens and camera from a known position. Then, a couple of weeks (or a month) later, take another picture with the same lens and camera. That'll show that there's effectively no difference.

That is very likely true...but nonetheless, it's appearance without the photo will be larger than usual for a full moon rising over the horizon...I think...I'm a bit concerned that the near full moon is presently rising about an hour before sunset, dimming its view... I saw it tonight, but arriving home late from work, it was about 20 minutes after moonrise and about 5 degrees or more above the east horizon, and the sun was also about 5 to 10 degrees above the west horizon, so the view of the moonrise was a non-event. I might have to wait until a couple of days after the equinox , when the moon rises just after sunset, to confirm my judgement of its apparent size. Time will tell.

 

[DaveC426913]

That is very likely true...but nonetheless, it's appearance without the photo will be larger than usual for a full moon rising over the horizon...I think...I'm a bit concerned that the near full moon is presently rising about an hour before sunset, dimming its view... I saw it tonight, but arriving home late from work, it was about 20 minutes after moonrise and about 5 degrees or more above the east horizon, and the sun was also about 5 to 10 degrees above the west horizon, so the view of the moonrise was a non-event. I might have to wait until a couple of days after the equinox , when the moon rises just after sunset, to confirm my judgement of its apparent size. Time will tell.

What I have yet to understand is how you will verify it.

Will you just look up at it and say "Yep, that's bigger"?

 

[PhanthomJay]

What I have yet to understand is how you will verify it.

Will you just look up at it and say "Yep, that's bigger"?

If it looks as big as the "Mothership" in that movie "Close Encounters of the Third Kind' (if you remember it), that's my verification. I would certainly encourage you to view it as well, to see what I think I mean. Certainly, I can judge a 10 inch (25 cm) pizza pie from a 16 inch (40 cm) pizza pie. The moon tonight near the horizon looked like the 10 inch/25 cm version. In a couple of nights, weather permitting, I'll judge its apparent size accordingly. And if I'm right, i'll say, "Yep, that's bigger"!

 

[DaveC426913]

If it looks as big as the "Mothership" in that movie "Close Encounters of the Third Kind' (if you remember it), that's my verification. I would certainly encourage you to view it as well, to see what I think I mean. Certainly, I can judge a 10 inch (25 cm) pizza pie from a 16 inch (40 cm) pizza pie. The moon tonight near the horizon looked like the 10 inch/25 cm version. In a couple of nights, weather permitting, I'll judge its apparent size accordingly. And if I'm right, i'll say, "Yep, that's bigger"!

Thank you. There were a couple of brain storage cells I was setting aside, giving you the benefit of the doubt, content to wait and see how this played out.

But since, as I've feared all along, your method for verification is utterly subjective and ultimately self-fulfilling (you'll see the Moon as big as you think you see it, no way for you to determine otherwise, let alone anyone else) - you've freed up those storage cells for me.


So I'll just provide my answer to tomorrow's post right now:

"Gee, there's a surprise."

 

[PhanthomJay]

But since, as I've feared all along, your method for verification is utterly subjective and ultimately self-fulfilling (you'll see the Moon as big as you think you see it, no way for you to determine otherwise, let alone anyone else) - you've freed up those storage cells for me.

See the 2 photos below for comparison. Now I know one is a telephoto, but can't you see , subjectively, that one is bigger than the other, without having to take a scale and measure it across the computer screen? Gee...

 

[cjl]

The fact that one is a telephoto completely ruins the comparison.

The thing is, in a telephoto lens, things look bigger. To have a legitimate comparison, take a picture with a camera and then take another picture in a few days with exactly the same lens settings.For example, I think you can plainly see that one of these looks bigger than the other:

http://blog.lib.umn.edu/draeg001/regionalpartnerships/snow moon.jpg
http://muneebastronomy.files.wordpress.com/2007/07/moon.jpg

That doesn't mean the moon actually changed size though - just that the image composition and camera settings are different.

 

[PhanthomJay]

The fact that one is a telephoto completely ruins the comparison.

The thing is, in a telephoto lens, things look bigger. To have a legitimate comparison, take a picture with a camera and then take another picture in a few days with exactly the same lens settings.


For example, I think you can plainly see that one of these looks bigger than the other:

http://blog.lib.umn.edu/draeg001/regionalpartnerships/snow moon.jpg
http://muneebastronomy.files.wordpress.com/2007/07/moon.jpg

That doesn't mean the moon actually changed size though - just that the image composition and camera settings are different.

You are missing the point...the full moon, when approximately the same distance from the earth, is always the same size, but due to the 'moon illusion', our brain makes it appear bigger, visually, forget the darn camera, when it's close to the horizon as compared to when its overhead. That's a given fact. What I am saying is that the Harvest Moon, when on the horizon at the Autumn Equinox (day of equal day and equal night at the Equator, September 22,23, this year) , appears bigger than other full moons when on the horizon. It may be due to its brightness and the fact that it is directly opposite the setting sun at the Equinox. I know the camera will prove otherwise, but my brain will say otherwise.