Flat Earth Tests

Flat-Earthers will, it seems, go to great lengths to prove that the Earth is not a globe. They will try to raise money, unsuccessfully, to travel to Antartica, perhaps in order to demonstrate that they will be turned away at gunpoint for the attempt.

They will buy fairly expensive cameras with powerful zoom lenses and use the zoom to somehow prove that the ships don't go over the horizon, or that faraway skylines are visible when they shouldn't be, or that stars are really blurry undulating masses.

They will shoot lasers across lakes in an attempt to debunk a similar (but notably not identical) experiment performed on the series Genius recently.  And they will measure the temperature, so they say, of moonlight compared to moon shade which, somehow, is supposed to prove that the Earth is flat. But what they won't do is perform a few simple, definitive tests that show whether or not the Earth is flat.

So, if you seriously think that the Earth is flat, forget about high-tech, GoFundMe campaigns, and vague, badly designed experiments. Be prepared to get out, reach out, and find out. Warning: there's math involved.

Test One: Measure a Sunset, Watch the Moon Set
I've talked about sunrise and sunset before, and gotten a lot of excuses about perspective. But perspective is a visual phenomenon, and we're going to ignore it. Instead, we are going to cast and measure some shadows, and do some trigonometry. If you're not particularly good at trig (it's okay, I'm not either), I'll point you to an online calculator that you can use to help out.

It helps to be on an ocean beach that faces west for this. A beach that faces east also works, but then you should watch the moon rise and measure the sunrise. And if you don't have access to a beach, any big field without any really tall surrounding mountains will work almost as well. I'm going to assume a west-facing beach.

Pick a clear evening when the moon is full or nearly full. It will be easier to see. For tools you'll need a yardstick, a tape measure, a compass, a small level, binoculars, and paper and pencil. Get yourself a spot at least an hour before sunset. Plunge the yardstick into the sand until two feet are sticking up. Use the level to make sure it's straight up and down.

Half an hour before sunset, measure the shadow cast by the stick, and use the compass to work out the direction of the shadow. Believe it or not, that's all the data you need to gather. After the sun has fully set and no longer casts any usable light, try to bring it back into view with the binoculars.

Bring the binoculars back to the beach half an hour before the moon sets. Watch the moon sink below the horizon, note it's apparent size, and whether the horizon cuts it off as it sinks. When it's out of sight, try to bring it back into view with the binoculars.

Now it's time to go home and do some evaluation of what you just did. Get out your simple data on the shadow. First, let's start with the length of the shadow. Open this triangle calculator. Erase any data already provided. In the box for side x, put the height of your stick, or two feet. In the box for angle a, put 90, since your stick formed a right angle with the ground. In the box for side z, put the length of the shadow, and click on "Calculate."

The key number is the angle that will show as opposite side 1 (the calculator should show side x and angle b; I don't know why it doesn't). This is the angle above the ground that the sun was when it cast it's shadow. In my test, it was 6.71 degrees. What does this say about the flat Earth? Well, let's apply this math in reverse.

The most common flat-Earth model has the sun 3000 miles above the "plane." Let's plug that back into the calculator: put 3000 into side x, erase side z, and put 6.71 into angle b. Calculate. Look at the figure for side 3. In my test, the stick cast a 17-foot shadow; if the sun were 3000 miles over a flat plane, it would be over 25,000 miles away at sunset. In other words, off the disc of the flat-Earth model.

Not a problem, you say? We know that when it's sunset where you're standing, it's noon somewhere else. Where else on Earth is 25,000 miles away? The model is breaking down.

Okay, what if the sun is not 3000 miles high? If the sunset happens when the sun is about 6000 miles away, which is one of the implications of the model, then how high would it be? Erase side x, put 6000 in side z (leaving the original figures for angles a and b). Calculate.

In my test, the sun would have to be 706 miles high to create that shadow. If you think that's possible, then it's time to go out and try to measure the height of the sun. I give you some idea of the difficulties of that task if you assume a flat Earth in this blog post. But before you go to the trouble, let's think about your other observations.

Get out your favorite azimuthal equidistant map projection, or another flat-Earth map if you have one. You can get the Gleason Map here.  Find yourself on the map. Then chart the angle of the sun based on the shadow angle you jotted down. Does it make any sense? In some lucky circumstances it might, but in most locations on most days, it won't match up.

When you watched the moon go down, it didn't shrink in size. It may have even looked a little larger as it came close to the horizon. And it moved down into the horizon, the horizon cutting through it until it sank out of sight. And you couldn't bring it back into view with the binoculars. So it wasn't just moving away from you. Relative to the ground, it was actually behind the ground. Same with the sun. Behind the curve. Because the Earth is curved.

I know of no other way to explain these observations. You're welcome to bring your own interpretation, but if it's vague, prepare to be challenged. Because on something as important as the truth, especially when you deign to rebuke a couple of thousand years of established scientific thought, you'd better be specific, or you'd better go home.

And if this doesn't convince you, the next experiment is designed to directly indicate that water does, contrary to flat-Earth myth, curve over the surface of the Earth.

Test Two: Revisit Wallace
Here's another test, which requires quite a bit more time and effort than the last, but directly indicates that standing water curves, and even gives you a way to approximate by how much.

It is a variation on the test performed by biologist Alfred Russell Wallace at the Old Bedford Level in 1870. You can read more about that event here. But it requires a long stretch of relatively still water with a line of sight over at least five miles. And if the water is not shallow, the process can be rather harrowing.

So, I'm calling on flat-Earthers who live in very cold climates to try a simpler variation. You'll need a sufficiently large body of water that freezes over so that it's perfectly safe to walk on. You'll also need three stepladders that are at least 10 feet high (Gorilla or Little Giant ladders would work well), two targets big enough to see from miles away with a telescope, some hardware to affix the targets to the top of the ladders, and a telescope. A spotting scope would be easier to use than the type designed for astronomy.

Set up the ladders so that one is about 2-1/2 to 3 miles away from the first. Affix a target to that ladder and measure its distance from the frozen surface. Set up another ladder so that it forms a line of sight with the other two, and is the same distance from the second as the second is from the first. Affix a target to it at the same height.

Now go back to the first ladder and set up the scope so that it is also the same height above the surface as the two targets. Aim the scope at the furthest target. If the Earth is flat, the first target will be in the way of the second. In the Earth is concave, as "Lord" Steven Christ claims, the first target will be below the second target. And if the Earth is convex (and it is), the first target will be higher than the second.

If you measure how much higher, by having someone with a cell phone move another target until it is centered in your scope, you can use that information to estimate to circumference of the Earth, not with any great accuracy, but close enough to know that the "official" circumference is definitely in the ball park.

Have I done this experiment? No. First, the sunset tells me what I need to know, and I don't feel the need to go to the trouble. Second, Wallace did this in 1870 and I have no reason to doubt his veracity. And third, if I did the experiment and published the results, the flat-Earthers would only reward my efforts by declaring them fake. See, for example, what happened to Wallace.

That said, when the lakes in my area freeze over this winter, I may suggest to one of the science teachers at the local high school that this would make an interesting project to show that direct evidence is available to anyone willing to access it and evaluate it with an unprejudiced eye.

The question is, are any flat-Earthers willing to go out into the cold and do the same? If you, though, do not have easy access to a large, frozen body of water, or don't wish to wait for the dead of winter, here's a third idea.

Test Three: Extend Eratosthenes

Since the last experiment involved either getting wet or waiting for lakes to freeze. there is a way to show whether or not the Earth is curved quite easily with the same equipment we used in the sunset experiment (those of us who actually bothered to do it), and some international cooperation.

Around 240 BCE, the librarian at the Library of Alexandria, Eratosthenes, devised a clever way to measure the circumference of the Earth. The method is described here for those who would like to repeat the experiment.

Flat-Earthers have pointed out that this experiment does not prove that the Earth is a sphere, because the same results could have been obtained from a close sun and a flat plane. And they are right about that; the experiment assumed a spherical Earth and a distant sun, because others before Eratosthenes had made compelling arguments to establish those facts, and Eratosthenes was only trying to figure out how big the Earth was.

But one little addition to the experiment would prove the sphericity of the Earth. And it is as simple as adding a third data point. Because the geometry of a curved surface does not match the geometry of a flat surface (see, for example this blog post of mine).

So, through the power of connecting over the Internet, all you need to do is find two people who live a latitudes quite a bit different from your own. More than two is even better. Each of you will need a yardstick, a level, and a measuring tape, and access to Time and Date and Google Maps.

I won't complicate this too much, because the details aren't nearly as important as the basic idea. You and your teammates choose a day, bury the yardsticks to the same depth, and measure the length of the sticks' shadows at solar noon (that's where Time and Date comes in). 

Google Maps will help determine the distances between the parallels from each location. Now, you can map out the triangulations on a flat plane, and then on a sphere and compare, but you can simplify it. Just assume a flat plane and try to use the triangulations to determine the distance to the sun. If the Earth is flat, and the sun is close, then the distances to the sun should be consistent. If they are not, then the assumptions of a flat plane and a close sun are incorrect.

Having determined that, you can then extend the math to conclude that the Earth is, indeed, a sphere, and that it was pretty close to the size that Eratosthenes worked out over 2200 years ago.


If you are unwilling to do even the simplest of these tests, and fully explain the results, then you really have no business confidently proclaiming that the Earth is not a sphere. There are many, many other proofs, of course, which flat-Earthers do some very fancy apologetics to get around (or ignore), but even very simple tests like these show that the entirety of the flat-Earth idea is absurd on its face and should be abandoned posthaste.


  1. http://www.atlanteanconspiracy.com/2015/08/200-proofs-earth-is-not-spinning-ball.html

    I recommend you looking into this article..

    1. Do you honestly think I haven't already read this? And have you noticed that nowhere in that document are there are tests performed by Dubay personally? And no verification of any of his claims?

      I have offered these tests to Dubay, and he has ignored me. He is unwilling to perform any real experiments, and is satisfied to regurgitate the work of others, not only about the flat Earth, but about other wild conspiracies as well.

      He is a hack, and a charlatan, and since I know he doesn't read my blog, you can tell him I said so.

    2. If you're simply denying all the points he refers to,without addressing them, I think you're refuting your own credibility in the matter. If nothing else, your arrogance of being a superior being than any others is revealing of possible racist views you might have. Why would you think you are at such a higher superiority than another rational and logical thinking person? And if you really want to claim he is irrational, will you be explaining it, or go back to your preconceived understanding of what you think you know, and how obsurd it is for his position.

      Just a curious atheist mind with no care of which side the chips may fall.

    3. Racist? Where does that comes from? Projecting, perhaps? I never said I was "superior." I just said that Dubay is a charlatan and a hack; that is not, actually, a judgement on his intelligence, about which I know too little to evaluate. Rowbotham was a charlatan (though not a hack), but a very intelligent one.

      Read what I wrote about Dubay. I have addressed many of his "proofs" in this blog and my book, and I don't intend to repeat all of that in the comments section. If you want to know what I have to say about flat-Earth "evidence," then take the time to read my other posts.

      But more to the point is that Dubay doesn't do any original research; he gathers conspiracy garbage from others and scatters around like cheap fertilizer.

      If you intend to comment on my posts, I highly suggest you read at least some of the others before you deign to judge my motives, and please stay on the topic at hand.

      Which in the case of this post was getting flat-Earthers to get off their collective asses and do experiments that yield real data that others can evaluate, critique, and replicate.

    4. so what you mean is that you are so closed minded to think outside your box, perfect understood

    5. jcamaya, don't tell me what I mean. I mean I have read all the tripe in "200 Proofs" and Dubay can't think his way out of a paper bag. And neither can you if all you can do is throw accusations of "close-mindedness" at me while failing to perform any of the very simple tests I've proposed, or any others, to demonstrate that the Earth is flat.

      While you're at it, read my blog post entitled "Outside the Box" and then stop using that shopworn phrase, because you're beating it to death.

      Repeatedly saying that everyone except you enlightened "truthers" is indoctrinated does nothing to make your case.

      It's time for the flat-Earth idiots to put up or shut up. Get out there and do some real field work and publish real data using real math.

      Or better yet, see the error of your ways and get off the flat-Earth bandwagon.

    6. So this experiment proves what? That we don't know how far the sun is? That one flat earth model is wrong? That the universe can be infinite but the earth can't? This experiment does not necessitate any one particular conclusion. I personally don't mind that we don't have all the answers. I do know one thing though NASA's globe doesn't add up.

    7. Michael Owens, your comment, especially the phase "NASA's globe," proves that you are unwilling to think. Which means that explaining anything to you is an exercise in futility. But, as others may read your comment, I will try to put it in terms that even someone who thinks the Earth is flat can understand.

      I don't give a rat's ass what model of flat Earth you want to apply, although you don't seem to have one at all. Whether the "plane" is infinite or not doesn't matter one little bit. We, everyone we know, inhabit a portion that runs somewhere around 12,500 miles from the North Pole to the South Pole, or whatever you want to call them.

      As I write this, the sun is still pretty low in the sky here in New England. Were I to call my cousin in Scotland right now, he would tell me that the sun is high in the sky there. So any triangulation that puts the sun thousands of miles away from his location can't be right. And any triangulation based on a flat plane that puts the sun over his head (not directly of course, because that never happens in Scotland) will make the distance to the sun absurdly low.

      And I do mean absurdly. Because a sun that is so close would travel across the sky much faster near noon than at sunset, which we don't see, and it would look vastly larger at noon that at sunset, which we don't see (badly-shot YouTube videos notwithstanding).

      Flat-Earthers love to tell us all to do our own research, and trust our senses. But they don't actually want us to do that.

  2. A lovely view of the rotating sphere was watching the familiar 'Plough/Big Dipper' of constellation Ursa Major rising and setting in South India, when at home in northern England it's always above the horizon every night of the year. I wasn't thinking of it as proof of anything at the time as the idea of needing proof of the earth's shape would have been absurd, but the internet has since brought out this strange flat-earth belief so I've used it as an example a few times when they're asking how I can be so sure we're spherical. I'd like to think travelling to various latitudes and observing Polaris's position and the sky's movement around it should convince anyone of the earth's shape, but bearing in mind their invariably poor grasp of geometry and scale maybe it wouldn't be enough.
    Gretat blog anyway.. Keep up the good work.

  3. you're still assuming the sun is massive, millions of miles away (notice also how that distance has changed incredibly since copernicus) and sending light rays parallel to the earth's surface - i agree that would be ONE explanation of the phenomena you describe.

    but the other is that the sun is quite small, local, and radiates its light divergently (most photos show this,) and is certainly further refracted through the solid firmament, explaining the varying declinations of the sun between the solstices for most places away from the equator, sunrises/ sets, differing sizes of the sun in the sky, especially near the horizon (sometimes tiny, sometimes massive) and any other visual phenomena you care to name.

    couldn't agree with you more that the ae flat circle/ gleason's map/ model is bogus, and most flat earthers refuse to listen to their error, even from other flat earthers.

    what do i think? space is 4-dimensional and the 'universe' is bound by doors, not much bigger than the earth (25,000 miles long.)

    as to its height, maybe the same to the toppermost of the heavens, who knows?

    i know man has only flown as high as 69 miles up, and dug 8 miles down..

    1. Actually these experiments don't assume any of that. The sunset experiment tries to locate a close sun, and fails. The Wallace experiment has nothing to do with the sun. And the Eratosthenes experiment as I've framed it fails to find a consistent distance to the sun, which should be a cinch if the Earth is flat.

      You can bob and weave through excuses from the mythical dome, but you can't create any model for this dome which would perfectly match all observations from everywhere on the planet. But the globe model can, which makes it the only reasonable conclusion.

    2. Close sun and stars totally breaks down when you begin to take the shapes of constellations into account.

      If the earth were flat, then the only way to explain that different constellations are visible from different parts of the world, and at different times is to say that they are actually much closer to us.

      If it were true that the stars were actually much closer to us than believed, then the shapes of constellations would distort as they moved across the sky.

      Imagine for example a constellation that is an equilateral triangle when viewed directly above you. On a globe earth with stars that are distant, that constellation will stay the same shape, no matter where you view it from (as is seen in reality.)

      On a flat earth, with close stars, perspective would distort these constellations, squishing them as they moved closer to the horizon. As this does not happen there is literally no way the stars could be this close, unless the stars are actually moving to point at YOU specifically, you are the only real person in the world (so nobody else would notice this happening as you moved relative to them), everyone else including your close friends and family are actors (as they could call you from far away and confirm that the stars had magically changed otherwise) and the entire sky centered itself around you, no matter where you go. Now THAT is a crazy hypothesis, but a necessary one if you are trying to prove a flat Earth.

      Now don't go on about vanishing points or whatever, because that is a misunderstanding of perspective, and can be mathematically proven as false (and wouldn't even work in this case either).

    3. Michael, that's another test that could be done so easily with a little international Internet cooperation. Thanks!

  4. Arnt Inge Vistnes at the University of Oslo lies about how the Foucalt pendulum is both non-motorised and yet never needs to be reset, why does he lie about this?

    1. 1. Source, please, and by source I don't mean a video by a flat-Earther; I mean an original source.

      2. This is off-topic, and has nothing to do with the simple tests I've proposed which show whether or not the Earth is flat. Why don't you do some actual tests, supply links to the data here in the comments, and give your interpretation of the results? Why, for that matter, has NO FLAT-EARTHER done that?

  5. Someone in Manitoba had performed you mentioned test with a laser across a frozen lake. He found no evidence of curvature over 7.5 miles

    1. What is the obsession with flat-Earthers and lasers? Optical experiments close to the water—even if the water is frozen—are fraught with problems, including refraction, reflection (snow, for goodness sake), and laser beam spread.

      Long before lasers, Wallace was aware of the problems of working close to water, and that's why he set his targets high, to minimize that problem.

      So, no, this test was not done on the frozen lake in Manitoba; a poorly-designed, inconclusive test was performed. And I'm still waiting for any flat-Earther to do these tests as designed. Almost 2000 views on this page, and not one taker yet.

  6. What about the good ol' send-your-very-own-camera-into-near-space-to-look-at-the-curvature-for-yourself test? Understanding that camera lenses can cause distortion, but I believe you addressed that as well in a different post.


    1. Watching the footage, I see considerably evidence of curvature, especially since the horizon is always below the center line of the lens, and yet still looks curved slightly upward. Once you understand how lens distortion works, this is pretty damning for any thought of a flat horizon.

      Flat-Earthers will disagree, of course. They will claim that any lens distortion is evidence in their favor, and will reject this out of hand.

      Which explains, I think, why no flat-Earther has come back to me with data from doing any of the experiments I have described above.

  7. Hi Gordon, just a little extract from the usual 'debate' I am having with a Gleason Map supporter. You may want to add this to the tests (In a less long winded fashion of course) -

    Here is a test that I like.
    Take any portion of the Gleason map (I used Australia) and compare the east/west distance on the map, to the north/south distance. I used Perth to Sydney, and Adelaide to Darwin. then look at the same approximate distance using the drivings directions of your choice. I will use Google Maps.

    The distances I obtained from the map are (in map scale) approximately 30.64 cm Perth to Sydney and approximately 9.55cm Adelaide to Darwin. I chose these routes as they are 'generally' straight lines compared to other routes. You may choose others when you do the test if you think they represent your case better. (Remembering that distortion for this particular projection is least near the North Pole) So the ratio between a generally north south distance and a generally east west distance is approximately 1: 0.311. When using Google driving directions the distance from Perth to Sydney is approximately 3,940 km and Adelaide to Darwin is approximately 3,028 km. This is a ratio of approximately 1: 0.76.

    Now I have driven those roads a few times and agree with google on the approximate distance.

    If the Gleason Map was anywhere near what the real world looked like then if it was 3940 km from Perth to Sydney, then it would be 1225km from Adelaide to Darwin - nope. Or if you took the Darwin Adelaide distance to be true then it would be 3028 km from Adelaide to Darwin and 9,736 km from Perth to Sydney. Nope. Every single person driving any one of those roads proves that the Gleason map is not the shape of the real world. All day. Every day. No opinion required. As for the use as a badge by the UN - because this projection makes the world look round, which suits a badge.

  8. You can add to test: Length from Cairo to Gibraltar is half of Perth - Sydney on FE MAP. But in reality 1st one is almost 200km longer (3500) than that in Australi (3350)

    1. Flat-Earthers, especially those that call themselves "zetetics," will dismiss this because they claim not to have the resources to verify these distances. That's nonsense, of course, but a convenient excuse.

      The other excuse is that there is no set flat-Earth model, and the "flat-Earth map" (the azimuthal equidistant polar projection) is not the "real" flat Earth. They will claim that they don't know what the Earth really looks like, but they know it isn't a "spinning ball." How they know this, of course, gets quite vague and bizarre in pretty short order.

      But yes, any attempt to reconcile distances on the AEP with real-world distances will fail, progressively so as you travel south.

  9. After I wake up I thought of another ones. If there is no gravity on Earth how is that air don't go into space, followed by evaporating water? And when they come with density or something like that if density is making things fall down on earth why is this huge ball of fire (sun) don't go same way and fall on us?

    1. The flat Earth works in mysterious ways. Most flat-Earthers say that space does not exist. Many say that we are encased in a dome of some kind. As to what keeps the sun aloft and moving, there is usually some non-specific reference to electromagnetic energy. Why that doesn't make everything else fly in circles above the Earth is never explained.

      I saw a portion of a video by Mr. Thrive and Survive that claims that the sun has a negative charge and that the outer ring of the flat Earth has a positive charge and it keeps the sun moving between the Tropics. He never reconciles that with the fact that positive and negative poles attract, which should just stick the sun to one or the other.

      In short, the depth of thinking that goes into the flat Earth is proportionally much shallower than the layer of water that is the true Earth's oceans.


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