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Horizon

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Flash
309013.  Wed Apr 02, 2008 8:09 am Reply with quote

Would this be an interesting Gen Ig (not in the sense of a trick question, but something that people generally won't know)?

How far away is the horizon?

A: About 3 miles (for someone 6ft tall and standing upright at sea level the horizon is 2.83 nautical miles or 3.29 statute miles away).

http://www.boatsafe.com/tools/horizon.htm

Or maybe everybody knows this already? (I didn't, though - would have guessed more)

Better way of putting the question, maybe? And what goes in the notes?

 
eggshaped
309016.  Wed Apr 02, 2008 8:15 am Reply with quote

I'd have thought it was loads more instinctively, but then if I'd have thought about it, 3 miles seems about right.

I suppose you'd still be able to see a boat more than 3 miles away, just wouldn't be able to see the bottom of it?

 
Flash
309028.  Wed Apr 02, 2008 8:19 am Reply with quote

Yes, I suppose so. Likewise if you were sailing towards an island you'd see the mountain tops from much further away than 3 miles.

 
Flash
309046.  Wed Apr 02, 2008 8:33 am Reply with quote

And vice versa. If you're on the top of Mt Everest, the horizon is 230 miles away.

Incidentally, egg, it looks as though your "secondary peak on Everest" question might be back on as the boys have found a couple of much more convincing pictures. So maybe this question could link.

 
eggshaped
309047.  Wed Apr 02, 2008 8:35 am Reply with quote

"picture researchers"

No pics, just wanted to say thanks for the everest work, guys.

 
dr.bob
309085.  Wed Apr 02, 2008 9:28 am Reply with quote

I'd've definitely guessed way more than 3 miles for the horizon thing. Maybe a question along the lines of "How far would you need to sail away from a beach before you begin to disappear over the horizon?"

That way you're kind of implying that the observer is standing on the beach (i.e. also at sea level), and "begin to disappear" sidesteps any problems about when the top of you vanishes.

 
Flash
309092.  Wed Apr 02, 2008 9:40 am Reply with quote

Too complicated and also too limiting, I think. Good questions are very open - precision is the opposite of what we're after.

What stays three miles away from me but only 2 and three-quarter miles away from Andy (Hamilton)?

What's "as far as I can see"?

That kind of thing.

 
Flash
317574.  Wed Apr 16, 2008 9:30 am Reply with quote

This is going into the question basket:

Iím out windsurfing, Iíve got the wind, and Iím heading for the horizon. How far am I going?

About 3 miles - for someone 6ft tall and standing upright at sea level the horizon is 2.83 nautical miles or 3.29 statute miles away (ignoring the fact that it recedes as you approach it, of course).

Although the horizon is a function of the curvature of the Earth, its existence is not in itself a proof that the Earth is curved Ė there would still be a horizon if the Earth was flat. Indeed, for observers at sea level the difference would be imperceptibly small. For a moving observer itís a different story because the tops of ships and mountainous islands do appear over the horizon first, and that effect is attributable to curvature.

The distance to the horizon in miles is approx = the square root of 1.5x your height in feet (eg for a 6-footer 6 x 1.5 = 9, and root 9 = 3). The actual visual horizon is slightly farther away than the calculated visual horizon, due to the atmospheric refraction of light (so you can see round the bend a bit). All this is at sea level, of course; if you're on the top of Mt Everest, the horizon is 230 miles away.

In perspective the horizon is the line on which all horizontal lines converge. In astronomy it is the horizontal plane through the eyes of the observer. A sextant measures the altitude of a celestial body above the horizon.

 
Davini994
639222.  Sun Nov 22, 2009 9:49 am Reply with quote

Why would there still be a horizon if the Earth was flat?

 
gruff5
639230.  Sun Nov 22, 2009 10:12 am Reply with quote

I remember having a reverie about this as a kid.

Imagining a pair of railway tracks on a perfectly flat Earth going off into the distance, forever. Well, everyday railway tracks appear to go "up" in your visual field the further away they get from you. So, if they want on into the infinite flat distance, wouldn't they go up and up and up, until maybe they curved right around your head?

Then, later on, I realised it would be analgous to that Greek philosopher's arrow that travels halfway to a target, then halfway of the remaining distance, then halfway again and so, never arrives!

Those railway tracks would go "up" at an ever decreasing rate and would actually converge to a horizon and go no further. This horizon would be above the curved Earth horizon and would be perfectly horizontal (pun unavoidable) to your eyes.

 
Davini994
639253.  Sun Nov 22, 2009 11:03 am Reply with quote

Gruff5 wrote:
Then, later on, I realised it would be analgous to that Greek philosopher's arrow that travels halfway to a target, then halfway of the remaining distance, then halfway again and so, never arrives!

This is precisely my thinking then the horizon would be infinitely far away. Which is the same as saying that there isn't a horizon.

 
bobwilson
639281.  Sun Nov 22, 2009 12:06 pm Reply with quote

If you stood on the surface of a really massive body then the horizon would be more than 3 miles (if it was massive enough, you'd be able to see the back of your head).

 
CB27
639301.  Sun Nov 22, 2009 2:03 pm Reply with quote

If the earth was flat then various tall structures would be visible on a good day, so you'd be able to see various mountains, etc.

The best example is if you've been to places like Ayers Rock, because the land around is so flat, when you go a bit of a distance away you notie the bottom seems cut off all of a sudden, this couldn't happen on a flat Earth.

 
Sadurian Mike
639328.  Sun Nov 22, 2009 3:10 pm Reply with quote

You'd need very good, clear, air too see very far.

 
gruff5
639332.  Sun Nov 22, 2009 3:38 pm Reply with quote

In a closed universe, the flat Earth would curve up and over your head.

 

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