[garygreen]

I was replying to a post which argued that perspective is caused by lenses in the eye that focus things to a point and then sends the image back onto the retina. You are saying that you agree with me that it has nothing to do with lenses? Great.
...
Do you agree, then, that the world is presenting a certain angular size to you and that it is not your eye doing it?

the poster you replied to was explaining apertures to you, not lenses.  that's what your pupil is.

i'm replying to your argument that distant objects look smaller "because the world presents to us that they are shrunken."  especially wrt to the diagram you posted.  it makes no sense at all.  "things look smaller because they look smaller" is not an explanation.

the reason things appear smaller as they recede from us is not mysterious.  it's just angles.  as an object recedes, it subtends a smaller and smaller angle.  but this angle is always greater than zero.  the smallest angle one can possibly resolve is a function of aperture (in the ideal case).

that's basically it.  everything around you has a non-zero angular size, and there's a "smallest angle" your eyes can differentiate.  note that infinity is not required.

[TomInAustin]

That is because you were taught to imagine the world as in the left side of this image below, which is what the Ancient Greeks taught, what the educational system continues to teach today, and is a wrong interpretation of perspective geometry. We really view the world in accordance to perspective that culminates to a point, as the right side of this overhead image shows:

So what you are saying is that the farther something is away the smaller it appears?  Always?  Or just sometimes?

[Obviously]

Probably just when it’s convenient for him

[SiDawg]

Perspective is how the world presents itself to us, and has nothing to do with your eyeball.

Er, no, it has EVERYTHING to do with your eyeball. You know that a building in the distance is still the same height no matter how far away you are yes? It's only the image formed inside your eye that makes it appear smaller yes?

Perspective also happens to pinhole cameras which don't have lenses.

The purpose of a lens if to focus the light rays in to a single point. A pinhole camera doesn't need a lens: it IS the point. So yes, perspective happens with pinhole cameras. I still don't think you realise what perspective actually is... You can think of it as the angles formed by light in to the pin hole... there is still an "image" on the other side of the pinhole yes? So the further things move away, the smaller they appear in that image, because the angles between the top and the bottom and smaller... If the angles are smaller, then they project a smaller image...  I'm really not sure what you don't understand about this

Things shrink in the distance because the world presents to us that they are shrunken. They are not physically shrunken, but the world presents to us that they are. It has nothing to do with the lenses in your eye to cause the effect.

What?? If it's not the eye, then what is it? I really can't comprehend how to even respond to this nonsense. It's as if you think there's some sort of "magic" involved which "presents" a small image to your eye? It's not... it's light inside your eye hitting different points on your retina.

You are basically arguing that a tiny voracious bear 3 miles in the distance isn't really displayed by the world to you as tiny. It is only your eyeball causing it to be tiny. That is a ridiculous notion on several fronts.

That's perspective! The bear isn't literally smaller... the eye isn't "causing" it to be small... the light rays from the top of the bear and the light rays from the bottom of the bear, are entering your eye so very very close to each other, that the image projected on to your retina is very small... Larger angle, larger image... smaller angle, smaller image. You do understand how "lines" work right?

Take this image, from Johannes Kepler's "Astronomiae Pars Optica", published 1604 (not sure if it's an image from the book or derived). As the object described by A-B moves further away, then the image a-b gets smaller yes? We've known how the eye and perspective works for 400 years.

[George Jetson]

I have just wasted nearly 20 minutes watching the most jumbled explaination of why the stars rotate ets. It is a mixture of half truths, and jumping from one subject, to another with no connection.

OK Crepusculart rays. Even the actual ones in the very short clips he showed, (the “antcrepuscular” ones) not actually truly converge, but they do so in his diagrams, so they are not the same.

Secondly with the anti crepuscular rays the light source is behind your back, ie the sun. You never see the sun again when looking away from it. (This is important)

The light rays from the stars do not cause crepuscular rays, so there is no link between the 2, ie light from stars and crepuscular rays.

When looking at the stars they are in from of you, you are facing them, so the light cannot behave in the same way as anti crepuscular rays which are generated from behind you.

The light from the stars shine directly into your eyes, so there is no bending of the light source to a single point on the horizon. If that were the case then all of the stars if they were in a globe above us at fixed distance would by perspective be one single pinpoint of light.

In the video he makes massive jumps to conclusions that makes the South Pole star steady on the same bearing on the horizon at the same time, which is plainly wrong. What is also does not explain is why the relationship between the stars is the same.

I will give you an example of an actual observation i made last night.
We are in 20S latitude, and at about 19:00 lt, or 11:00Z o saw the constellation of Crux, (southern cross) with Acrux at an altitude of about 20 degrees above the horizon, and the long axis of Crux was about parallel with the horizon, pointing towards the South Pole star. At the same time of the night, in GMT about 11:00 hrs, someone in Fuji, with a similar lattitude, but 60degrees difference in longitude, at 23:00lt would have seen EXACTLY the same as i did, Acrux to the left of the South Pole star, Cruz long axis above the horizon, about 20 degrees Alrtitude, and parallel to the horizon, the only difference would have been it would have been 4 hours later in local time.

Finally his representation of the stars is rubbish. When he imposes the star movements over the earth, with the “apparent” movement to an observer on the equator, does he not realise that he has stars on the NE of the equator disappearing as they get near the equator, then Re appearing after they pass overhead, and finally spreading out towards the edges?

In reality stars DO NOT look like that. I am guessing he has never actually seen stars on the equator, or at different points whilst travelling from north to south.
The angles or distances between stars does not change. If i measure an anglular distance from Alpha Centurii to Acrux I will get a reading, and that reading WILL BE THE SAME pretty much wherever i am on the earth when the 2 are visible. The same goes for the stars over the equator. When we are next on the equator i will do this at different time of the night, proving “perspective” cannot apply to stars.

P Brain is an adequate title for him if he thinks he has proven anything. It is more like smoke and mirrors of a magic trick, keeping you distracted with a load of rubbish, to distract the audience from the real reasons. Ie the earth is Round.

Pity Tom started a new thread as i already explained most of this post in my other thread. On the examination of the movement of stars

You completely failed to grasp p-brane's argument.  He isn't arguing that the stars produce crepuscular rays, he uses crepuscular rays as an example of how perspective works.  His argument is premised upon the idea that the stars are on the same plane (on some sort of rotating stellar disc) and that the appearance of some of the stars appearing to be higher or lower is due to their distance from the observer.

[George Jetson]

The people on opposite sides of the earth would only see stars at night. It is not night for two people on opposite sides of the earth at the same time; and so whoever is in night is experiencing Sigma Octantis sweep across their half of the earth.

It can very easily be night for people on opposite meridians if they are at a sufficient latitude. Anywhere that you have more than 12 hours of darkness in winter can have observers at opposite sides of the earth observing sigma octantis at the same time.

Santiago, Chile and Perth, Australia are nearly 180 degrees of longitude apart, and both around 30 degrees south, so both could be expected to see sigma octantis at the same time every night for months during winter. Given the lack of people objecting to star charts being inaccurate, I think it is likely that this is the case.

This is a highly questionable claim (their time zones are 13 hours apart).  Evidence?

[Curious Squirrel]

The people on opposite sides of the earth would only see stars at night. It is not night for two people on opposite sides of the earth at the same time; and so whoever is in night is experiencing Sigma Octantis sweep across their half of the earth.

It can very easily be night for people on opposite meridians if they are at a sufficient latitude. Anywhere that you have more than 12 hours of darkness in winter can have observers at opposite sides of the earth observing sigma octantis at the same time.

Santiago, Chile and Perth, Australia are nearly 180 degrees of longitude apart, and both around 30 degrees south, so both could be expected to see sigma octantis at the same time every night for months during winter. Given the lack of people objecting to star charts being inaccurate, I think it is likely that this is the case.

This is a highly questionable claim (their time zones are 13 hours apart).  Evidence?

Santiago, Chile: 33.4489° S, 70.6693° W
Perth, Australia: 31.9505° S, 115.8605° E

About 5° off being 180° opposite one another. Time zones aren't exact straight lines either. Not by a long shot.

[rabinoz]

The people on opposite sides of the earth would only see stars at night. It is not night for two people on opposite sides of the earth at the same time; and so whoever is in night is experiencing Sigma Octantis sweep across their half of the earth.

It can very easily be night for people on opposite meridians if they are at a sufficient latitude. Anywhere that you have more than 12 hours of darkness in winter can have observers at opposite sides of the earth observing sigma octantis at the same time.

Santiago, Chile and Perth, Australia are nearly 180 degrees of longitude apart, and both around 30 degrees south, so both could be expected to see sigma octantis at the same time every night for months during winter. Given the lack of people objecting to star charts being inaccurate, I think it is likely that this is the case.

This is a highly questionable claim (their time zones are 13 hours apart).  Evidence?

Santiago, Chile: 33.4489° S, 70.6693° W
Perth, Australia: 31.9505° S, 115.8605° E

About 5° off being 180° opposite one another. Time zones aren't exact straight lines either. Not by a long shot.

I doubt that Santiago, Chile and Perth, Australia can be in darkness at the same time but try:
Santiago, Chile: 33.4489° S, 70.6693° W
Sydney, Australia: 33.8688° S, 151.2093° E
UTC time = Thursday, 21 June 2018 at 09:10:00.
And it will be much the same in 2019.

Mind you it's full moon and Sigma Octantis and nearby stars are barely visible to the unaided eye at the best of times.
The Southern Cross (Crux) and its "pointers" (Alpha and Beta Centauri) are far brighter but about 30° from the South Celestial Pole.

[edby]

You are basically arguing that a tiny voracious bear 3 miles in the distance isn't really displayed by the world to you as tiny. It is only your eyeball causing it to appear to be tiny. That is a ridiculous notion on several fronts.

Fixed that for you.