# how did flat-earth believers explain the horizon? **URL:** \ **Category:** Factual Questions\ **Created:** [August 20, 2009, 5:18am UTC](https://boards.straightdope.com/t/how-did-flat-earth-believers-explain-the-horizon/507040 "2009-08-20T05:18:34Z")\ **Posts on this page:** 9\ **Page:** 3
**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:** [August 21, 2009, 4:48pm UTC](https://boards.straightdope.com/t/how-did-flat-earth-believers-explain-the-horizon/507040/41 "2009-08-21T16:48:42Z")
> [@astorian](#): > > Christians have gotten many things wrong about science, but the shape of the Earth was never among them. This is one of the things that baffles me about a board with such normal quality as the SDMB. I see it way too often here. Let me point out something: Not all Christians believe the same thing. So if Christian A believes the Earth is round in no way shape or form means that Christian B can’t believe the Earth is flat, complete with Bible quotes. You need to keep this in mind when making such posts. * * * How I would challenge a Flat Earther: Call the opposite side of the world. E.g., from here to Australia. Right now it is midday here. It’s just turning light in Melbourne. Shoot, nowadays you don’t even have to call someone. I just Googled for some webcam shots. How can the Sun be high up in the sky here and not visible at all from everywhere on a flat Earth? Ditto call someone in the southern hemisphere and ask them if they see Polaris at night. Or the seasons or … . Any explanation basically would come down to magic. ---
**Author:** ![vinniepaz](https://avatars.discourse-cdn.com/v4/letter/v/b4bc9f/32.png) [@vinniepaz](https://boards.straightdope.com/u/vinniepaz)\ **Post date:** [August 21, 2009, 6:20pm UTC](https://boards.straightdope.com/t/how-did-flat-earth-believers-explain-the-horizon/507040/42 "2009-08-21T18:20:06Z")
Fight my ignorance… Why would a flat Earth even have a horizon? I was under the impression that the horizon is a direct result of the curvature of the Earth, as shown under “true horizon” in this picture: > **[File:Horizons.svg](https://en.wikipedia.org/wiki/File:Horizons.svg)** > > Original file ‎(SVG file, nominally 679 × 430 pixels, file size: 3 KB) > македонски > español > In case this is not legally possible: Acdx grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law. ---
**Author:** ![Freddy\_the\_Pig](https://avatars.discourse-cdn.com/v4/letter/f/a587f6/32.png) [@Freddy\_the\_Pig](https://boards.straightdope.com/u/Freddy_the_Pig)\ **Post date:** [August 21, 2009, 6:23pm UTC](https://boards.straightdope.com/t/how-did-flat-earth-believers-explain-the-horizon/507040/43 "2009-08-21T18:23:55Z")
> [@vinniepaz](#): > > Why would a flat Earth even have a horizon? Because a flat earth would only be below you, not above you. If you lifted your eyes above the horizon-tal (get it?), you’d see only sky, just like today. ---
**Author:** ![vinniepaz](https://avatars.discourse-cdn.com/v4/letter/v/b4bc9f/32.png) [@vinniepaz](https://boards.straightdope.com/u/vinniepaz)\ **Post date:** [August 21, 2009, 6:30pm UTC](https://boards.straightdope.com/t/how-did-flat-earth-believers-explain-the-horizon/507040/44 "2009-08-21T18:30:56Z")
right, but why would it be finite (i.e. a line)? why wouldn’t you be able to see mountains hundreds of miles away? im having a hard time formulating this question… what would determine the distance to the horizon? on wiki, it says the distance to the true horizon on a curved earth is sqrt(13h). what would it be on a flat Earth? ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [August 21, 2009, 6:39pm UTC](https://boards.straightdope.com/t/how-did-flat-earth-believers-explain-the-horizon/507040/45 "2009-08-21T18:39:43Z")
You could see forever on a flat earth if there was nothing else preventing you. However, atmospheric effects (opacity, refraction, etc) could limit how far you can see. Refraction bends your line of sight so you don’t see along straight lines. Opacity is anything that absorbs light along your line of sight–fog, smog, dust, etc. I’m sure there’s other mechanism that could limit sight. ---
**Author:** ![vinniepaz](https://avatars.discourse-cdn.com/v4/letter/v/b4bc9f/32.png) [@vinniepaz](https://boards.straightdope.com/u/vinniepaz)\ **Post date:** [August 21, 2009, 6:53pm UTC](https://boards.straightdope.com/t/how-did-flat-earth-believers-explain-the-horizon/507040/46 "2009-08-21T18:53:13Z")
> [@Pleonast](#): > > You could see forever on a flat earth if there was nothing else preventing you. However, atmospheric effects (opacity, refraction, etc) could limit how far you can see. Refraction bends your line of sight so you don’t see along straight lines. Opacity is anything that absorbs light along your line of sight–fog, smog, dust, etc. I’m sure there’s other mechanism that could limit sight. Interesting. So is it refraction that would cause a linear horizon? ---
**Author:** ![Flymaster](https://avatars.discourse-cdn.com/v4/letter/f/c4cdca/32.png) [@Flymaster](https://boards.straightdope.com/u/Flymaster)\ **Post date:** [August 21, 2009, 6:55pm UTC](https://boards.straightdope.com/t/how-did-flat-earth-believers-explain-the-horizon/507040/47 "2009-08-21T18:55:39Z")
> [@friedo](#): > > You can see it next time there is a lunar eclipse. And the ancient Greeks knew how those worked. (Well, except for the whole heliocentricity thing, but that’s largely irrelevant.) Doesn’t this really just show me that it’s a disc, and perfectly parallel to the sun-disc and moon-disc? ---
**Author:** ![NoJustice](https://avatars.discourse-cdn.com/v4/letter/n/ecb155/32.png) [@NoJustice](https://boards.straightdope.com/u/NoJustice)\ **Post date:** [August 21, 2009, 7:28pm UTC](https://boards.straightdope.com/t/how-did-flat-earth-believers-explain-the-horizon/507040/48 "2009-08-21T19:28:08Z")
> [@Pleonast](#): > > No, it has exactly the effect I’m imagining–a finitely distant horizon. That is an explanation for why we see the tops of ships before the bottoms of ships when they’re at a distance. > > Now, you are correct that the same refraction will cause a bowl-like optical effect. Measurements looking for that could be used to disprove that refraction is not significant. And thus the explanation is wrong. > > But it’s still an explanation that flat earthers could use. ??? I don’t get it. How would refraction cause you see the tops of ships first? You would see them from slightly above. That’s not the same thing. It wouldn’t create a horizon, it would remove it. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [August 21, 2009, 7:49pm UTC](https://boards.straightdope.com/t/how-did-flat-earth-believers-explain-the-horizon/507040/49 "2009-08-21T19:49:34Z")
Oops, I’m getting the two refraction cases mixed. Downward refraction (optical density decreasing with altitude) gives the bowl effect, it’s upward refraction (optical density increasing with altitude) that mimics the effect of a downward-curving earth. [Previous page](https://boards.straightdope.com/t/how-did-flat-earth-believers-explain-the-horizon/507040.md?page=2)