# How can one prove that the earth is a sphere (or close to it)? **URL:** \ **Category:** Factual Questions\ **Created:** [October 15, 2018, 11:50am UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973 "2018-10-15T11:50:12Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![bizerta](https://avatars.discourse-cdn.com/v4/letter/b/3be4f8/32.png) [@bizerta](https://boards.straightdope.com/u/bizerta)\ **Post date:** [October 15, 2018, 11:50am UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/1 "2018-10-15T11:50:12Z")
Yesterday, on CBS Sunday Morning, they had a segment on flat-earthers. Are these people just ignorant or are they putting us on? I was once on a cruise ship at sea on a pristine cloudless evening. As I stood on the deck, I watched the sun disappear below the horizon. As soon as the sun vanished, I ran up a flight to the next deck and witnessed the sun setting again about 10 seconds later. What are some other simple ways we, as common folk, can demonstrate that the earth is round? ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [October 15, 2018, 11:53am UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/2 "2018-10-15T11:53:48Z")
The fact that no one has ever come to an edge. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [October 15, 2018, 11:57am UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/3 "2018-10-15T11:57:24Z")
> [@running\_coach](#): > > The fact that no one has ever come to an edge. To paraphrase Scott Kelly on _Wait Wait Don’t Tell Me_, if there were an edge don’t you think that’d be a cool place to visit? ---
**Author:** ![mcgato](https://avatars.discourse-cdn.com/v4/letter/m/ac8455/32.png) [@mcgato](https://boards.straightdope.com/u/mcgato)\ **Post date:** [October 15, 2018, 11:58am UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/4 "2018-10-15T11:58:55Z")
The circumference of the earth was estimated in about 240 BC by [Eratosthenes.](https://en.wikipedia.org/wiki/Eratosthenes#Measurement_of_the_Earth's_circumference) That pretty much implies that the earth is spheroid. ---
**Author:** ![Alpha\_Twit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alpha_twit/32/265_2.png) [@Alpha\_Twit](https://boards.straightdope.com/u/Alpha_Twit)\ **Post date:** [October 15, 2018, 12:01pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/5 "2018-10-15T12:01:04Z")
Lunar eclipses As the Earth passes between the Sun and Moon, it always produces a circular shadow. It’s not possible for a flat, disk like Earth to always produce such a shadow. Only a nearly spherical world can do that. > [@bizerta](#): > > Are these people just ignorant or are they putting us on? I don’t see these conditions as being mutually exclusive. ---
**Author:** ![bizerta](https://avatars.discourse-cdn.com/v4/letter/b/3be4f8/32.png) [@bizerta](https://boards.straightdope.com/u/bizerta)\ **Post date:** [October 15, 2018, 12:16pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/6 "2018-10-15T12:16:38Z")
> [@Alpha\_Twit](#): > > Lunar eclipses > > As the Earth passes between the Sun and Moon, it always produces a circular shadow. It’s not possible for a flat, disk like Earth to always produce such a shadow. Only a nearly spherical world can do that. OP here. I like this proof. On the CBS segment, one flat-earther had a model where both the sun and moon were above the horizon and ran in a circle above the earth. After all, both the sun and the moon are each visible somewhere at any point in time. So, if the sun and moon were both above the flat earth, what is casting a shadow on the moon? ---
**Author:** ![Alpha\_Twit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alpha_twit/32/265_2.png) [@Alpha\_Twit](https://boards.straightdope.com/u/Alpha_Twit)\ **Post date:** [October 15, 2018, 12:39pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/7 "2018-10-15T12:39:35Z")
> [@bizerta](#): > > OP here. I like this proof. [Watch this video from Neil deGrasse Tyson.](https://www.youtube.com/watch?v=hLPPE3_DVCw) I consider NDT to be a pompous ass but he communicates complex science issues well and he can be a most useful mammal. ---
**Author:** ![Munch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/munch/32/5281_2.png) [@Munch](https://boards.straightdope.com/u/Munch)\ **Post date:** [October 15, 2018, 12:58pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/8 "2018-10-15T12:58:00Z")
> [@bizerta](#): > > OP here. I like this proof. > > On the CBS segment, one flat-earther had a model where both the sun and moon were above the horizon and ran in a circle above the earth. After all, both the sun and the moon are each visible somewhere at any point in time. So, if the sun and moon were both above the flat earth, what is casting a shadow on the moon? They deny this proof by saying that the moon is self-illuminating, and that lunar eclipses are the moon cycling through something. It’s irrefutable in its pure lunacy. Those are the arguments that I think are good at just being able to point at the flat earth movement and hold them up as crackpots. What I find to be a solid argument is time lapse photos of the stars from the northern hemisphere, the equator, and the southern hemisphere, side-by-side-by-side. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [October 15, 2018, 1:08pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/9 "2018-10-15T13:08:41Z")
> [@Alpha\_Twit](#): > > Lunar eclipses > > As the Earth passes between the Sun and Moon, it always produces a circular shadow. It’s not possible for a flat, disk like Earth to always produce such a shadow. Only a nearly spherical world can do that. Good news and bad news. The bad news: A lot of shapes other that spheres produce circular shadows from every angle. [Meissner Bodies](https://en.wikipedia.org/wiki/Reuleaux_tetrahedron#Meissner_bodies) (relatives of the Reuleaux triangle), for example. The good news: These are more complicated than spheres, would require quite extraordinary Physics to explain why the Earth has that shape, etc. A lot of simple things can show deep problems with Flat Earth nonsense. E.g., why can’t people in the N. Hemisphere see stuff at the celestial S. pole and vice versa. Call someone on the opposite side of the Earth and ask them what time of day it is. And on and on. Of course a few Flat Earthers come up with Magical “Physics” to explain this and a million other things. But outside of simple drawings and such they have no real Math, Physics, experiments, data, etc. to back them up. ---
**Author:** ![Novelty\_Bobble](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@Novelty\_Bobble](https://boards.straightdope.com/u/Novelty_Bobble)\ **Post date:** [October 15, 2018, 1:41pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/10 "2018-10-15T13:41:26Z")
> [@mcgato](#): > > The circumference of the earth was estimated in about 240 BC by [Eratosthenes.](https://en.wikipedia.org/wiki/Eratosthenes#Measurement_of_the_Earth's_circumference) That pretty much implies that the earth is spheroid. I was going to post exactly the same point. The beauty of it being that it is something that can be easily replicated by any suitably motivated flat-earth nutjob. You need two groups of people, some sticks and string if you are feeling technical and the ability to roughly measure distance and manipulate angles by means of simple formula. It is one the great experiments of that, or any age. ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [October 15, 2018, 1:43pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/11 "2018-10-15T13:43:53Z")
> [@running\_coach](#): > > The fact that no one has ever come to an edge. That’s not a definitive proof. ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [October 15, 2018, 2:02pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/12 "2018-10-15T14:02:32Z")
> [@Alpha\_Twit](#): > > Lunar eclipses > > As the Earth passes between the Sun and Moon, it always produces a circular shadow. It’s not possible for a flat, disk like Earth to always produce such a shadow. Only a nearly spherical world can do that. I like this proof too, but I wonder how the Flat Earthers argue against it. About the recent solar eclipse, on the wiki page for [Modern flat Earth societies](https://en.m.wikipedia.org/wiki/Modern_flat_Earth_societies#Resurgence_in_the_era_of_celebrity_and_social_media), > [@](#): > > The solar eclipse of 21 August 2017 gave rise to numerous YouTube videos purporting to show how the details of the eclipse prove the Earth is flat. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 15, 2018, 2:17pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/13 "2018-10-15T14:17:09Z")
**ftg** , those shapes don’t cast circular shadows. [Here’s a picture of some](https://www.thingiverse.com/thing:649488). **Bullitt** , want to lay odds that the argument, in full, consists of “the details of the eclipse prove that the Earth is flat!”, with no actual calculations? ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [October 15, 2018, 2:17pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/14 "2018-10-15T14:17:13Z")
> [@Bullitt](#): > > That’s not a definitive proof. In this case it is since we’ve circumnavigated the Earth both East-West and North-South, so we’ve exhausted the search space. We can’t prove that there isn’t a hole through the Earth we haven’t found in this way, but I don’t see any flat earth model that would allow this kind of circumnavigation. ---
**Author:** ![Alpha\_Twit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alpha_twit/32/265_2.png) [@Alpha\_Twit](https://boards.straightdope.com/u/Alpha_Twit)\ **Post date:** [October 15, 2018, 2:28pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/15 "2018-10-15T14:28:07Z")
> [@Voyager](#): > > In this case it is since we’ve circumnavigated the Earth both East-West and North-South, so we’ve exhausted the search space. We can’t prove that there isn’t a hole through the Earth we haven’t found in this way, but I don’t see any flat earth model that would allow this kind of circumnavigation. No, according to Flat-Earth logic, that’s no more definitive than if you said that someone you know saw Sasquatch, Santa Claus and the little dog from the old Taco Bell commercials downing tequila shooters at last year’s cinco de mayo celebration. It’s an anecdote. What kind of physical, tangible proof can you show me that you personally have made that journey? Oh, you have none? Well then you’re just lying to support the conspiracy! ---
**Author:** ![Patch](https://avatars.discourse-cdn.com/v4/letter/p/a183cd/32.png) [@Patch](https://boards.straightdope.com/u/Patch)\ **Post date:** [October 15, 2018, 2:29pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/16 "2018-10-15T14:29:06Z")
> [@bizerta](#): > > Yesterday, on CBS Sunday Morning, they had a segment on flat-earthers. Are these people just ignorant or are they putting us on? There are a lot of really stupid people out there. [CoolHardLogic](https://www.youtube.com/user/CoolHardLogic) has some wonderful YouTube videos debunking their nonsense, along with the geocentrists. They’re fascinating to watch not just for the animation, but the elegant simplicity of the math and physics. ---
**Author:** ![bizerta](https://avatars.discourse-cdn.com/v4/letter/b/3be4f8/32.png) [@bizerta](https://boards.straightdope.com/u/bizerta)\ **Post date:** [October 15, 2018, 2:37pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/17 "2018-10-15T14:37:10Z")
> [@Munch](#): > > They deny this proof by saying that the moon is self-illuminating, and that lunar eclipses are the moon cycling through something. It’s irrefutable in its pure lunacy. Those are the arguments that I think are good at just being able to point at the flat earth movement and hold them up as crackpots. … OP here. When they interviewed some of these nuts, they also said that the moon landing was a hoax, so no one is on the moon to create the illusion of an eclipse “cycling”. How do these whack-a-doodles explain how we know, in advance, when a lunar eclipse will occur. ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [October 15, 2018, 3:10pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/18 "2018-10-15T15:10:14Z")
> [@Munch](#): > > They deny this proof by saying that the moon is self-illuminating, and that lunar eclipses are the moon cycling through something. It’s irrefutable in its pure **lunacy**. Those are the arguments that I think are good at just being able to point at the flat earth movement and hold them up as crackpots. > > What I find to be a solid argument is time lapse photos of the stars from the northern hemisphere, the equator, and the southern hemisphere, side-by-side-by-side. [emphasis added] You might not have intended that pun, but it’s the best one ever. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [October 15, 2018, 3:12pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/19 "2018-10-15T15:12:11Z")
> [@Bullitt](#): > > That’s not a definitive proof. Is there even a point to looking for a “definitive proof” for flat-Earthers? Just for fun, I looked up what they believe the edge is. Apparently, it’s an ice shelf, Antarctica. [Like this](https://www.ebay.com/i/323211894158?chn=ps&var=512286476111). ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [October 15, 2018, 3:19pm UTC](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973/20 "2018-10-15T15:19:14Z")
Evidence gathered through the use of science is easily dismissed through the use of idiocy. [Next page](https://boards.straightdope.com/t/how-can-one-prove-that-the-earth-is-a-sphere-or-close-to-it/822973.md?page=2)