[9 out of 10 doctors agree]

Dr. Rowbotham postulates that disappearing due to perspective occurs at "the angular limits of the eye", asserting that the angular limit is around 1 arcminute.

I disagree with Round Earthers that disappearing from perspective is completely ridiculous. I can actually name the Airy disk as a mechanism for it.

The Airy disk is a pattern of rings created by diffraction. For the human eye in bright light, the limit is about 1 arcminute. Additionally, multiple point sources of light can appear to merge like so:



Given this mechanism, I can hypothesize the following:

• An object close to disappearing due to perspective should be significantly blurred.
• There should be a pattern of rings, if it is indeed blurred from the Airy disk.

[Curious Squirrel]

I don't think I've seen anyone suggest that "disappearing from perspective is completely ridiculous" but rather that Rowbotham applies it to things or in ways that don't follow the known laws of optics. Such as the sun maintaining a crisp outline the whole time, as well as remaining unchanging in size. Or the bottom of a tower vanishing before the much smaller tip/top.

I do like this Airy disk thing though, have not heard of it before. I would posit that your hypothesis sounds reasonable though.

[Bobby Shafto]

Dr. Rowbotham postulates that disappearing due to perspective occurs at "the angular limits of the eye", asserting that the angular limit is around 1 arcsecond.

In Chapter XIV he writes "The smallest angle under which an object can be seen is upon an average, for different sights, the sixtieth part of a degree, or one minute in space."

[9 out of 10 doctors agree]

Dr. Rowbotham postulates that disappearing due to perspective occurs at "the angular limits of the eye", asserting that the angular limit is around 1 arcsecond.

In Chapter XIV he writes "The smallest angle under which an object can be seen is upon an average, for different sights, the sixtieth part of a degree, or one minute in space."

Typo, now fixed.

[Tontogary]

So how does the sun disappear when it measures about 31.5 to 32.5 arc minutes at sunset??? Too big to disappear due to the vanishing point. It never ever gets small enough, or low enough, or well, everything that FET says happens when it disappears, slowly, bit by bit below the horizon..........

[SiDawg]

So this is what we know:

• Parallel lines never meet
• Parallel lines or objects, as seen through the eye (or a camera lenses) will be "angled" towards a vanishing point
• The vanishing point is an infinite distance away
• Distance objects appear smaller in our field of vision because all images are focused to a point inside our eye
• At a certain distance, the eye can not discern whether two parallel objects are still separate or not

This is what flat earthers "know"

• Distant objects appear smaller for some reason
• At a certain distance, the eye can not discern whether two parallel objects are still separate or not
• I can see the sun disappear, therefore that must be the point where two parallel paths meet the vanishing point
• I can't draw a scale drawing, but I can draw a representation of that, by drawing a diagonal line for the sun and the earth and showing them meet somewhere
• I know I don't have to provide any more thought behind that because I'm happy with what ENAG shows me

The facts behind how perspective work are compatible with the flat earth "simplified representation" of how perspective works. Drawing representations of things is an important part of relaying information and teaching new concepts to people, provided they KNOW it is just a representation, and KNOW where that representation falls down. Flat Earth doesn't seem to be able to make that leap.

It is demonstrably, mathematically, and logically impossible for three parallel lines to reach a vanishing point independently... That is essentially what they're saying. There are three parallel paths: the ground, the bottom point of the sun, the top point of the sun. If the bottom point of the sun is parallel with the earth, then the top point is ALSO parallel with the ground. If the bottom point of the sun appears to meet/touch the earth, then the top part of the sun would meet/touch the earth at exactly the same point. As the bottom point of the sun gets closer and closer to that point, then the top point of the sun also gets closer and closer to the same point. Ergo, the top point and bottom point should meet at that point, and should appear to be getting closer and closer to that point as they approach it. In other words: the sun would shrink to a single point.

[rabinoz]

Dr. Rowbotham postulates that disappearing due to perspective occurs at "the angular limits of the eye", asserting that the angular limit is around 1 arcminute.

Who is arguing? Though to be precise that angular limit of around 1 arcminute is not as Rowbotham postulates the "vanishing point" due to perspective but the typical resolution limit.
Have a look at Notes on the Resolution and Other Details of the Human Eye.
And more:

The Limits of Human Vision
Highest resolution perceivable pixels: 28 seconds of arc.
Several physical factors limit the highest spatial frequencies that can be perceived by the human eye. The diffraction limit of the pupil, the foveal cone spacing, neural trace and physiological tests all agree on a maximum perceived frequency of approximately one cycle per arcminute (half arc-minute pixels). This is under optimal conditions, including100% contrast. While not quite directly comparable, so-called “20/20” vision represents detecting image features twice as large

From: The Limits of Human Vision, Michael F. Deering

I disagree with Round Earthers that disappearing from perspective is completely ridiculous. I can actually name the Airy disk as a mechanism for it.

What do you base your claim on that "Round Earthers" think "that disappearing from perspective is completely ridiculous"?
All we disagree with is claims that the ships, buildings and even the sun and moon disappear due to perspective rather than being hidden behind "something".

The Airy disk is a pattern of rings created by diffraction. For the human eye in bright light, the limit is about 1 arcminute. Additionally, multiple point sources of light can appear to merge like so:

But an Airy disk is a limit on the spot size determined by the wavelength of the light. The resolution of the eye or a camera is determined by the spacing of the receptor cells (or pizels).

Given this mechanism, I can hypothesize the following:

• An object close to disappearing due to perspective should be significantly blurred.
• There should be a pattern of rings, if it is indeed blurred from the Airy disk.

Yes, if it's due to the Airy disk.

This so-called 1 minute of arc is not a limit of visibility, just a limit on the eye's ability to separate objects, as illustrated in your photos.
There is no lower limit to the size object that can be seen provided there is enough contrast between it and the background and the eye receives enough light from it.

How Far Can the Human Eye See a Candle Flame?
Answers on the Web vary from a few thousand meters to 48 kilometers.
Now a pair of physicists have carried out an experiment to find out.

See the details in: How Far Can the Human Eye See a Candle Flame?

The result claimed is:

We show that a candle flame situated at ~2.6 km (1.6 miles) is comparable in brightness to a 6th magnitude star with the spectral energy distribution of Vega. The human eye cannot detect a candle flame at 10 miles or further, as some statements on the web suggest.

A 6th magnitude star is regarded as about the limit of unaided vision.
Guessing the candle flame as 15 mm high x 5 cm wide, its angular size would be: 0.02 x 0.007 minutes of arc - far smaller than the resolution limit of the eye.

This is just a quick example, but the visibility distance of a bright object against a dark background is limited only by the brightness.

Now what Globe supporters object to is the flat earthers' claims than the sun and moon can disappear and appear to set due to perspective.
The moon, for example, is supposedly about 50 km in diameter and when setting would typically be about 15,000 km away, so its angular size would be about 11 minutes of arc, so should easily be visible.
But what is so wrong with even this is that when overhead the angular size of the moon averages about 31 arcminutes and that size is virtually unchanged when it is setting - where's your "perspective"?

[hexagon]

Dr. Rowbotham postulates that disappearing due to perspective occurs at "the angular limits of the eye", asserting that the angular limit is around 1 arcminute.

I disagree with Round Earthers that disappearing from perspective is completely ridiculous. I can actually name the Airy disk as a mechanism for it.

The Airy disk is a pattern of rings created by diffraction. For the human eye in bright light, the limit is about 1 arcminute. Additionally, multiple point sources of light can appear to merge like so:



Given this mechanism, I can hypothesize the following:

• An object close to disappearing due to perspective should be significantly blurred.
• There should be a pattern of rings, if it is indeed blurred from the Airy disk.

That's a bit too naive approach. The full diffraction pattern you can only observe for diffraction at single object. Maybe you remember from school diffraction at a slit, double slit or grating. The pattern is basically the square of the Fourier transform of your diffracting object. In case of the the Airy disc, this is a point like object or a tiny hole.

What you see with your eye or if you take a picture with a camera is the convolution of the object and the point spread function of your imaging system. The point spread function is basically the image of a single point that you get due to the limited aperture of your eye or camera. The higher order fringes are not visible in this convoluted image, you just observe the blurriness. Due to this blurriness and depending of the contrast of the imaged objects, more and more details are getting lost.   

[hexagon]

But an Airy disk is a limit on the spot size determined by the wavelength of the light. The resolution of the eye or a camera is determined by the spacing of the receptor cells (or pizels).

I don't know for the eye, but for an ideal camera the pixel size should be smaller than the size of the Airy disc, something like a factor of 1.5 is ideal. The camera should be limited by diffraction, not by pixel size. On the other hand, pixels should not be much smaller, because you don't gain anything regarding resolvable information. That's sometimes funny if people buy a smartphone with tens of megapixel, but a crappy lens :-) 

[rabinoz]

But an Airy disk is a limit on the spot size determined by the wavelength of the light. The resolution of the eye or a camera is determined by the spacing of the receptor cells (or pizels).

I don't know for the eye, but for an ideal camera the pixel size should be smaller than the size of the Airy disc, something like a factor of 1.5 is ideal. The camera should be limited by diffraction, not by pixel size. On the other hand, pixels should not be much smaller, because you don't gain anything regarding resolvable information. That's sometimes funny if people buy a smartphone with tens of megapixel, but a crappy lens :-)

Much earlier than this I meant to quote the pixel pitch of some typical digital cameras, but things got in the way.

On the large size is the 24mm x 36mm sensor of the full frame digital SLR's with say 25 MPixels. The pixel spacing here is about 5.7 µm
down to say the iPhone X where the dual-12MP wide-angle camera has a 1.22 µm and the telephoto camera has a 1.0 µm pixel size.

These can be compared to the wavelength of green light of 0.55 µm.

But even excellent 25 MPixel digital SLR's are then limited by the lens resolution.