Suddenly, A Flat Earther Appears!

TheGnome said:
No what I'm saying is that with the assumptions mentioned in the gifs a flat earth would be fully consistent with the facts about the shadows presented.
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How? On a flat earth, all shadows regardless of location would be equal length and parallel. This is not what is observed.
 
Jrrarglblarg said:
"Convincing to you" is not the metric by which we judge the validity of science. It's that Argument From Incredulity again. It doesn't prove what you think it proves.

The standalone presentation was a short description of a longer experiment done ages ago. If you doubt it can be done, prove it with numbers. As I said upthread, you could replicate the experiment yourself, strictly on paper or in meatspace. Our forum population spans the globe, we could probably do it tomorrow if we can organize a couple of people in the right places. I'm at latitude 40.17 North. You?
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I am at
49.77277° N, -94.49098° E
 
arthwollipot said:
How? On a flat earth, all shadows regardless of location would be equal length and parallel. This is not what is observed.
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That's going to depend on the sun's distance from the earth. Hence the comment upthread about the Chinese misconcluding the sun was close to a flat planet (which seems inconsistent with what the ancient Chinese astronomers and mathematicians were up to in their day).
 
Jrrarglblarg said:
"The guy" is Carl Sagan. If you don't know who he is I suggest Google. He did not tell a unique story -he was merely providing a recitation of it as a segment of his show Cosmos while making a larger point.

"IMHO" is an opinion. Opinions are not facts. It is a fact that the shadows of identical length poles will cast different length shadows at the same time of the same day depending on latitude. In your opinion this is not possible; fine, but presenting your doubting opinion without supporting information is called "Argument From Incredulity," a form of logical fallacy. It is also a variant form of Argument From Authority in which you present yourself and your opinion as some form of authority on the issue of shadow length or something.

If you doubt the veracity of the story I suggest using references and calculations to prove to us just how much difference in shadow length results from difference in latitude and prove that this amount of data is insufficient. I think we could do it with solar data tables used by builders and architects, just on paper, with data easily found on the Internet.

Alternatively you could replicate the experiment on your own. If you know someone who lives substantially north or south of your location you could do it tomorrow using nothing more than a yardstick and email. You might be surprised how accurate your results are with even that rough data.
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Nowhere did I doubt that the earth is more or less spherical and the sun is about 8 lightminutes away. A long time ago I even delved a bit into celestial mechanics, equations and all.

I also am not aware of having said anything about shadows not being of different length at different places.

All I'm saying is that the logic presented in the gifs is not quite compelling.

When Carl Sagan presented this, he certainly did not do so in a void as happened here. I would say he was quite aware of the fact that for this chain of reasoning to be sound we have to know that the sunrays that hit the earth are highly parallel. But this is not mentioned in the gifs.

I think the omission of this crucial fact in the presentation is quite a serious fault. I mean one more slide?

Oh and MHO is just with respect to the evaluation of the presentation. With respect to the facts I'm not so humble.
 
Jrrarglblarg said:
"Convincing to you" is not the metric by which we judge the validity of science. It's that Argument From Incredulity again. It doesn't prove what you think it proves.

The standalone presentation was a short description of a longer experiment done ages ago. If you doubt it can be done, prove it with numbers. As I said upthread, you could replicate the experiment yourself, strictly on paper or in meatspace. Our forum population spans the globe, we could probably do it tomorrow if we can organize a couple of people in the right places. I'm at latitude 40.17 North. You?
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Sorry I did see this post only after I replied to the other one.

I'm truly at a loss to understand how you could take a denial of science from my posts.

My issue is not with the science but with this presentation of science.
Namely: If you omit a crucial link in a chain of reasoning, your conclusion is not valid. It may still be true though.

My latitude is 46,98 N and I know full well how to determine it in a clear night with the help of a sextant (well in principle anyway). A long time ago I even found my way home with the help of the polar star.
 
TheGnome said:
Sorry I did see this post only after I replied to the other one.

I'm truly at a loss to understand how you could take a denial of science from my posts.

My issue is not with the science but with this presentation of science.
Namely: If you omit a crucial link in a chain of reasoning, your conclusion is not valid. It may still be true though.

My latitude is 46,98 N and I know full well how to determine it in a clear night with the help of a sextant (well in principle anyway). A long time ago I even found my way home with the help of the polar star.
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That's great. There's also an app for that, not to mention a thing called GPS
 
TheGnome said:
Sorry I did see this post only after I replied to the other one.

I'm truly at a loss to understand how you could take a denial of science from my posts.

My issue is not with the science but with this presentation of science.
Namely: If you omit a crucial link in a chain of reasoning, your conclusion is not valid. It may still be true though.

My latitude is 46,98 N and I know full well how to determine it in a clear night with the help of a sextant (well in principle anyway). A long time ago I even found my way home with the help of the polar star.
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I suppose I was confused because this is not new information but apparently this is your first time encountering the story. I saw the Cosmos episode when it was originally broadcast and even then it wasn't the first time I'd heard it. So I have more contextual understanding of what Erastothenes was doing and how he did it, and figured every one would by now. Sorry.

Edit to add
If this gif is your only exposure to this experiment I suggest at least looking for Cosmos episodes at you library or on YouTube. I'm pretty sure Sagan includes the parallel rays of our sun as part of his explanation not included in the gif. Beyond that, it's an interesting story by itself. The wikipedia article is fairly complete but more detail would be required to turn it into a screenplay of any decent length.
 
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Jrrarglblarg said:
I suppose I was confused because this is not new information but apparently this is your first time encountering the story. I saw the Cosmos episode when it was originally broadcast and even then it wasn't the first time I'd heard it. So I have more contextual understanding of what Erastothenes was doing and how he did it, and figured every one would by now. Sorry.

Edit to add
If this gif is your only exposure to this experiment I suggest at least looking for Cosmos episodes at you library or on YouTube. I'm pretty sure Sagan includes the parallel rays of our sun as part of his explanation not included in the gif.
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Seems I can't express myself properly. In my defense it's my third language.

I know the story of Erastothenes quite well. Maybe that's why I spotted the missing link in the logic in the gifs. In every telling of it I remember the paralellity of the sunrays forms an important part of his reasoning. Without that he has nothing. I just regard this as a flaw in the presentation. It cannot stand alone. But maybe it wasn't meant to.

Again if it is used standalone it is lacking.
 
TheGnome said:
O come on. You really think this would be true with the sun being say 500km above a flat earth?
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That idea is adequately debunked by other evidence, so I don't believe that it should be under consideration at all.

A sphere - specifically, a slightly eccentric oblate spheroid - is the only shape that is possible given the evidence.

How can the flat earth hypothesis explain the observed fact that when a ship sails away from shore, its mast is the last thing to disappear over the horizon? A flat earth wouldn't have a horizon at all, let alone one that ships appear to sink down below. How can a flat earth explain the observed fact that the higher from the ground you are, the further you can see? If the earth were flat, you'd be able to see the same distance - in fact, to the other side of the earth - no matter how high off the ground you are.

Eratosthenes' demonstration isn't the smoking gun for a spherical earth. It's merely one piece of evidence among many. As others have said, it wasn't even done to prove that the earth was round - that was already well-known. It was done to calculate its diameter.
 
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arthwollipot said:
I've seen that explained. I wonder if TheGnome will explain it in the same way.
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Erastothenes did not prove a spherical earth. This fact was known long before. It was inferred e.g. by the nature of the earth's shadow on the moon during an eclipse.

A spherical earth was his starting point. What he did was determine its size. For that he used a rather simple geometrical argument. In it he used three facts that were well known by then.

First the earth is spherical. That enabled him to use the circle with its well understood properties.

Second the sunrays arrive on earth almost perfectly parallel. That made the math quite simple.

Third the earth is rotating on its axis and he had to know its orientation. That enabled him to choose 2 locations with the same longitude and to time the measurement.

That's my take on what he did. It was an impressive achievement and I never doubted it in this whole thread. Nor did I in any way doubt what science does know about the solar system.

But when I look at the presentation under discussion (that by the way doesn't outline the work of Erastothenes), I don't find the slide to mention that the sun is not small but far away :p. And without that the logic is just not sound.

I get it that today everybody that is not a flat-earther knows this very well by his teens at the latest and he fills in the missing bits with ease. But then this presentation doesn't tell him much new anyway.

But to teach the intelligent uninformed, or to convince a flat-earther even, such details are important to make a valid argument.

Now I take it that the presentation was not meant to be standalone so I give it some slack. But even so, it outlines an argument for a curved earth and leaves out a basic ingredient which would have needed just one aditional slide! Without it the conclusion is just not valid.

I can only assume that this was an oversight by Sagan.
 
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