# How far away is the horizon?

**URL:** <https://boards.straightdope.com/t/how-far-away-is-the-horizon/456951>\
**Category:** Factual Questions\
**Created:** [July 18, 2008, 1:55pm UTC](https://boards.straightdope.com/t/how-far-away-is-the-horizon/456951 "2008-07-18T13:55:43Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![I\_Have\_Hippos\_In\_My\_Garden](https://avatars.discourse-cdn.com/v4/letter/i/4491bb/32.png) [@I\_Have\_Hippos\_In\_My\_Garden](https://boards.straightdope.com/u/I_Have_Hippos_In_My_Garden)\
**Post date:** [July 18, 2008, 1:55pm UTC](https://boards.straightdope.com/t/how-far-away-is-the-horizon/456951/1 "2008-07-18T13:55:43Z")

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When you are sitting on your balcony looking out at the sea to the horizon, how far away is the line where the sea meets the sky? It always looks the same distance away, so how do you work it out?

(can you tell i’ve just come back from a holiday by the sea? 😉 )

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**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\
**Post date:** [July 18, 2008, 1:58pm UTC](https://boards.straightdope.com/t/how-far-away-is-the-horizon/456951/2 "2008-07-18T13:58:07Z")

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[Horizon](http://en.wikipedia.org/wiki/Horizon) on Wiki. Roughly, the distance is SQR(13\*h), where h is the height above ground level.

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**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\
**Post date:** [July 18, 2008, 2:22pm UTC](https://boards.straightdope.com/t/how-far-away-is-the-horizon/456951/3 "2008-07-18T14:22:45Z")

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[Here](http://boards.straightdope.com/sdmb/showthread.php?t=474381)’s a recent thread on basically the same subject, with calculations 'n stuff.

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**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\
**Post date:** [July 18, 2008, 3:58pm UTC](https://boards.straightdope.com/t/how-far-away-is-the-horizon/456951/4 "2008-07-18T15:58:46Z")

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Doesn’t refraction have to be taken into account? A la those stories of sailors in the arctic seeing ships which were actually several hundred miles away?

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**Author:** ![Giles](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/giles/32/60_2.png) [@Giles](https://boards.straightdope.com/u/Giles)\
**Post date:** [July 18, 2008, 4:22pm UTC](https://boards.straightdope.com/t/how-far-away-is-the-horizon/456951/5 "2008-07-18T16:22:11Z")

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[QUOTE=Q.E.D.]  
[Horizon](http://en.wikipedia.org/wiki/Horizon) on Wiki. Roughly, the distance is SQR(13\*h), where h is the height above ground level.  
[/QUOTE]

And in that formula, distance is in km while height (h) is in metres. If you want other units, you would need to change the 13.

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**Author:** ![chacoguy](https://avatars.discourse-cdn.com/v4/letter/c/50afbb/32.png) [@chacoguy](https://boards.straightdope.com/u/chacoguy)\
**Post date:** [July 18, 2008, 5:18pm UTC](https://boards.straightdope.com/t/how-far-away-is-the-horizon/456951/6 "2008-07-18T17:18:11Z")

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I really noticed this on a recent trip to Nebraska. I’m about two meters tall so my horizon is a bit over 5km. or about 3.5 miles. Not very far compared to where I live. On a good day, I can see mountains as far away as 150 miles. I think this adds to why Nebraska seems so flat. You’re expecting to see distant objects, but they have dropped away below the horizon.