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> You can trivially deomonatrate that the earth is round using basic tools available 2000 years ago. It's not actually so trivial. There are simple observation

> You can trivially deomonatrate that the earth is round using basic tools available 2000 years ago. It's not actually so trivial. There are simple observations that are consistent with a Round Earth model, but it's pretty difficult to nail things down rigorously and precisely. Anyway, it's sort of interesting to me that you even bring that up. My comment didn't really claim anything about Flat Earth at all; it was more an open statement about the epistimics of scientific knowledge among non-experts. The fact that you and one other commenter come to defend Round Earth, seems to suggest a sort of belief tribalism in our current science-oriented zeitgeist.

eesmith 9y ago
Questions about rigor and precision are a function of your goal. The goal is to determine if a Round Earth model is a more useful model than a Square or Disk Earth model. I've demonstrated it empirically to my own satisfaction. I've seen the Southern Cross right at the horizon from the Florida Keys, but not visible father north. I've seen that the North Star rises higher in the sky as I've gone north. And in summer I've seen that the daytime is much longer in Michigan than Florida, and how the sunlight in the evening goes through the windows of the north side of buildings, which it doesn't really do in Miami. I've driven across the US and seen that the sun rises a couple of hours later in the West than the East. I've been below the Equator, and seen Orion cross the sky upside down, while the Southern Cross and the Magellanic Clouds were high in the sky. I also got confused when driving because it turns out my sense of direction was based on the expectation that the Sun should be in the south at midday, not in the north. I was once at about 55 degrees north latitude, in early December, and the sun was low in the sky at noon. By measuring the shadow length I calculated the latitude to within a couple of degrees. (This calculation does require knowing the axial tilt, which I have not independently measured.) These are all consistent with a Round Earth model, and not at all consistent with any description of a Flat Earth model that I've come across. Now of course it's possible to say that I've not measured the radius of the Earth to sufficient precision, or demonstrated that the diameter between the poles is shorter than the equatorial bulge. But that's changing the goalposts. I did not have to appeal to any authorities to confirm that the round earth model is a much better fit to my observations than a flat earth one. Why are you not able to make similar empirical tests? If you are able to carry them out, why are they not enough for you? The TV series "Ring of Truth" from the 1980s tried to address the question of how you can test things out for yourself. One of the things they did, in such a way that you could reproduce their work, was to drive along a long north-south road and measure the elevation change in a star. From this they could estimate the size of the Earth. They call it the "Van of Eratosthenes." You can see it at https://www.youtube.com/watch?v=yRY2SkMTafc https://www.youtube.com/watch?v=yRY2SkMTafc . Again, there's no reason to trust what the said. Rather, you can use it to reproduce their methods yourself, which is the sort of empirical test you asked about.
- xelxebar 9y ago
  Thanks for sharing those stories. It sounds like you pay quite a bit of attention to the sky and stars! > Why are you not able to make similar empirical tests? If you are able to carry them out, why are they not enough for you? I'm guessing you meant these as rhetorical questions. They're indeed good for introspection. For clarity though, I'm perfectly satisfied with a globe Earth. Seems to be a pretty good model for my needs. I was actually hoping sidestep discussions of Flat Earth vs Round Earth since, as you point out, the empirical observations aren't to hard to think up as a lay person. They're not quite trivial enough to be done in your backyard though. What I'm more interested in, personally, are questions like "What is the structure of the Earth's interior?" I learned an answer from a textbook and am vaguely aware of how seismic data has been used to extrapolate this, but I'm not quite sure how to come up with a Core + Mantle + Crust model myself. Instead of brute forcing these things, I'd really like to hear some clever reasoning and Fermi estimation capable of rederiving these standard results. Perhaps easier to answer would be "Does the moon have an atmosphere?" One idea I had was to point a telescope on a line of site tangent to the lunar surface and look for abberations in starlight compared to stars a large angular distance away. This seems doable in your backyard with relatively cheap hardware.
  - eesmith 9y ago
    I was responding to your statement "It's not actually so trivial. There are simple observations that are consistent with a Round Earth model, but it's pretty difficult to nail things down rigorously and precisely." I object to the idea that additional rigor and precision is needed for the specific case you were responding to. As to your overall topic, one step is to watch that miniseries I mentioned earlier, "The Ring of Truth: An Inquiry into How We Know What We Know". It gives several examples of working things out from scratch. For example, drop a measured and small amount of olive oil onto a still pond. It produces an oil patch. The volume of the oil divided by the size of the patch gives an upper bound for the size of the molecules in olive oil. What you might not know is that there is a large amount of literature in repeating some of the classic experiments. For example, physics undergraduate lab courses may have the students measure the strength of the Earth's local magnetic field, or the value of the gravitational constant G (not g, which is the acceleration due to gravity), and do so using basic equipment you can gather or make yourself. Detecting the Earth's structure on your own is difficult. You will need a seismometer, and learn how to interpret it. A quick search shows there are many hobby plans for building your own seismometer, or you can buy ones made for schools. The harder part is to come to trust that P-waves and S-waves are different, that they have different speeds, that one cannot go through liquid, and that observations of many earthquakes from around the world can be combined with an understanding of material science and thermodynamics to produce a model of the interior of the Earth. If your purpose is to avoid what you consider to be appeals to authoritative sources, you will have to redo from scratch what took others several lifetimes to develop. One of these is Francis Birch, https://en.wikipedia.org/wiki/Francis_Birch_(geophysicist) https://en.wikipedia.org/wiki/Francis_Birch_(geophysicist) . Quoting that Wikipedia page, "In 1952 he demonstrated that Earth's mantle is chiefly composed of silicate minerals, with an inner and outer core of molten iron." Concerning the round earth model, what you can do given limited travel is to create a Foucault pendulum, or visit somewhere which has one set up. In principle this can be done in a backyard, but it required a long pendulum wire and still air - do you have an empty corn silo in your backyard? The time it takes to go around can be used to calculate your latitude. However, this only shows that you are in a rotating reference frame. You then need to repeat what the ancient Greeks did, and look at lunar eclipses to see that the shadow of the earth is always a circle, no matter where the Moon is in the sky. These together mean that from your backyard you could (in principle) determine that the Earth is a rotating round object. Concerning your question "Does the moon have an atmosphere?", the problem is, the Moon does have an atmosphere. It's very thin - https://en.wikipedia.org/wiki/Atmosphere_of_the_Moon https://en.wikipedia.org/wiki/Atmosphere_of_the_Moon . A naked eye view of the Moon is enough to determine that it does not have an extremely thick atmosphere. So with a backyard telescope all you can do is set an upper bound for the thickness of the atmosphere. But to do that, you need some way to predict what those aberrations might look like. For example, if it had a CO2 atmosphere that was 0.1 bar at the surface, would you be able to detect it? Have you measured the index of refraction of different gasses, or are you willing to trust the measurements of others. I'm not saying it's impossible, but rather that you have to decide at some point where you can trust the results of others.
dragonwriter 9y ago
> There are simple observations that are consistent with a Round Earth model, but it's pretty difficult to nail things down rigorously and precisely. It's quite possible to both demonstrate that the Earth is round and get an accurate first-order approximation of its size with tools available 2,000+ years ago. We know this is possible with certainty because it was actually done 2,000+ years ago, by Eratosthenes.
Spooky23 9y ago
I referenced “round earth” because it is so trivial to demonstrate with tools available to almost everyone. A subset of people are able to directly observe the earths curvarure from ships, aircraft or outer space. There are people in the space station right now who looking at the round earth. The notion that the earth is flat is absurd to all but the ignorant. There’s a reason why skeptics target things like round vs. flat earth — it’s a variant of “the big lie” approach used by oppressive political regimes. As humans, we dig into and push back against nuanced arguments. But when you challenge fundamental things, people who are actively ignorant and charismatic have an easier time convincing people about nonsense. A similar example is the UFO phenomenon of the 80s and 90s, where the military planted or encouraged wacky stories to divert attention from aircraft and cruise missile testing.

eesmith 9y ago

Questions about rigor and precision are a function of your goal. The goal is to determine if a Round Earth model is a more useful model than a Square or Disk Earth model. I've demonstrated it empirically to my own satisfaction. I've seen the Southern Cross right at the horizon from the Florida Keys, but not visible father north. I've seen that the North Star rises higher in the sky as I've gone north. And in summer I've seen that the daytime is much longer in Michigan than Florida, and how the sunlight in the evening goes through the windows of the north side of buildings, which it doesn't really do in Miami. I've driven across the US and seen that the sun rises a couple of hours later in the West than the East. I've been below the Equator, and seen Orion cross the sky upside down, while the Southern Cross and the Magellanic Clouds were high in the sky. I also got confused when driving because it turns out my sense of direction was based on the expectation that the Sun should be in the south at midday, not in the north. I was once at about 55 degrees north latitude, in early December, and the sun was low in the sky at noon. By measuring the shadow length I calculated the latitude to within a couple of degrees. (This calculation does require knowing the axial tilt, which I have not independently measured.) These are all consistent with a Round Earth model, and not at all consistent with any description of a Flat Earth model that I've come across. Now of course it's possible to say that I've not measured the radius of the Earth to sufficient precision, or demonstrated that the diameter between the poles is shorter than the equatorial bulge. But that's changing the goalposts. I did not have to appeal to any authorities to confirm that the round earth model is a much better fit to my observations than a flat earth one. Why are you not able to make similar empirical tests? If you are able to carry them out, why are they not enough for you? The TV series "Ring of Truth" from the 1980s tried to address the question of how you can test things out for yourself. One of the things they did, in such a way that you could reproduce their work, was to drive along a long north-south road and measure the elevation change in a star. From this they could estimate the size of the Earth. They call it the "Van of Eratosthenes." You can see it at https://www.youtube.com/watch?v=yRY2SkMTafc https://www.youtube.com/watch?v=yRY2SkMTafc . Again, there's no reason to trust what the said. Rather, you can use it to reproduce their methods yourself, which is the sort of empirical test you asked about.

xelxebar 9y ago
Thanks for sharing those stories. It sounds like you pay quite a bit of attention to the sky and stars! > Why are you not able to make similar empirical tests? If you are able to carry them out, why are they not enough for you? I'm guessing you meant these as rhetorical questions. They're indeed good for introspection. For clarity though, I'm perfectly satisfied with a globe Earth. Seems to be a pretty good model for my needs. I was actually hoping sidestep discussions of Flat Earth vs Round Earth since, as you point out, the empirical observations aren't to hard to think up as a lay person. They're not quite trivial enough to be done in your backyard though. What I'm more interested in, personally, are questions like "What is the structure of the Earth's interior?" I learned an answer from a textbook and am vaguely aware of how seismic data has been used to extrapolate this, but I'm not quite sure how to come up with a Core + Mantle + Crust model myself. Instead of brute forcing these things, I'd really like to hear some clever reasoning and Fermi estimation capable of rederiving these standard results. Perhaps easier to answer would be "Does the moon have an atmosphere?" One idea I had was to point a telescope on a line of site tangent to the lunar surface and look for abberations in starlight compared to stars a large angular distance away. This seems doable in your backyard with relatively cheap hardware.
- eesmith 9y ago
  I was responding to your statement "It's not actually so trivial. There are simple observations that are consistent with a Round Earth model, but it's pretty difficult to nail things down rigorously and precisely." I object to the idea that additional rigor and precision is needed for the specific case you were responding to. As to your overall topic, one step is to watch that miniseries I mentioned earlier, "The Ring of Truth: An Inquiry into How We Know What We Know". It gives several examples of working things out from scratch. For example, drop a measured and small amount of olive oil onto a still pond. It produces an oil patch. The volume of the oil divided by the size of the patch gives an upper bound for the size of the molecules in olive oil. What you might not know is that there is a large amount of literature in repeating some of the classic experiments. For example, physics undergraduate lab courses may have the students measure the strength of the Earth's local magnetic field, or the value of the gravitational constant G (not g, which is the acceleration due to gravity), and do so using basic equipment you can gather or make yourself. Detecting the Earth's structure on your own is difficult. You will need a seismometer, and learn how to interpret it. A quick search shows there are many hobby plans for building your own seismometer, or you can buy ones made for schools. The harder part is to come to trust that P-waves and S-waves are different, that they have different speeds, that one cannot go through liquid, and that observations of many earthquakes from around the world can be combined with an understanding of material science and thermodynamics to produce a model of the interior of the Earth. If your purpose is to avoid what you consider to be appeals to authoritative sources, you will have to redo from scratch what took others several lifetimes to develop. One of these is Francis Birch, https://en.wikipedia.org/wiki/Francis_Birch_(geophysicist) https://en.wikipedia.org/wiki/Francis_Birch_(geophysicist) . Quoting that Wikipedia page, "In 1952 he demonstrated that Earth's mantle is chiefly composed of silicate minerals, with an inner and outer core of molten iron." Concerning the round earth model, what you can do given limited travel is to create a Foucault pendulum, or visit somewhere which has one set up. In principle this can be done in a backyard, but it required a long pendulum wire and still air - do you have an empty corn silo in your backyard? The time it takes to go around can be used to calculate your latitude. However, this only shows that you are in a rotating reference frame. You then need to repeat what the ancient Greeks did, and look at lunar eclipses to see that the shadow of the earth is always a circle, no matter where the Moon is in the sky. These together mean that from your backyard you could (in principle) determine that the Earth is a rotating round object. Concerning your question "Does the moon have an atmosphere?", the problem is, the Moon does have an atmosphere. It's very thin - https://en.wikipedia.org/wiki/Atmosphere_of_the_Moon https://en.wikipedia.org/wiki/Atmosphere_of_the_Moon . A naked eye view of the Moon is enough to determine that it does not have an extremely thick atmosphere. So with a backyard telescope all you can do is set an upper bound for the thickness of the atmosphere. But to do that, you need some way to predict what those aberrations might look like. For example, if it had a CO2 atmosphere that was 0.1 bar at the surface, would you be able to detect it? Have you measured the index of refraction of different gasses, or are you willing to trust the measurements of others. I'm not saying it's impossible, but rather that you have to decide at some point where you can trust the results of others.

dragonwriter 9y ago

> There are simple observations that are consistent with a Round Earth model, but it's pretty difficult to nail things down rigorously and precisely. It's quite possible to both demonstrate that the Earth is round and get an accurate first-order approximation of its size with tools available 2,000+ years ago. We know this is possible with certainty because it was actually done 2,000+ years ago, by Eratosthenes.

Spooky23 9y ago

I referenced “round earth” because it is so trivial to demonstrate with tools available to almost everyone. A subset of people are able to directly observe the earths curvarure from ships, aircraft or outer space. There are people in the space station right now who looking at the round earth. The notion that the earth is flat is absurd to all but the ignorant. There’s a reason why skeptics target things like round vs. flat earth — it’s a variant of “the big lie” approach used by oppressive political regimes. As humans, we dig into and push back against nuanced arguments. But when you challenge fundamental things, people who are actively ignorant and charismatic have an easier time convincing people about nonsense. A similar example is the UFO phenomenon of the 80s and 90s, where the military planted or encouraged wacky stories to divert attention from aircraft and cruise missile testing.