How far is the horizon???

[BMM389EC]

A bit trivial, but I was wondering how far is the horizon, on land???

[Matthewjharvey]

Depends what the visibility is.

[BMM389EC]

Assuming good visiblilty......where the sky meets the land.

[GoneWest]

I remember standing on the 'prom' at Blackpool during my early flight training days....and looking at gas rigs in the Irish Sea...could just see the tops of them...looked on the chart and measured them at 21 nautical miles.

If you wanna go any further above sea level...all bets are off (use the VHF R/T formula!!)

[DownIn3Green]

Don't know how far, but I do know you never get there...

[Four Seven Eleven]

Distance to horizon

At a height h above the ground, the distance to the horizon d, is given by:

d = sqrt(2*R*h/b)
b=0.8279 is a factor that accounts for atmospheric refraction and depends on the atmospheric temperature lapse rate, which is taken to be standard. R is the radius of the earth. Note that the earth is assumed smooth- likely only true over the oceans!

For h in feet and d in nm:

d =1.17*sqrt(h)
i.e. from 10000 feet, the horizon is 117nm away

(Reference Bowditch American Practical Navigator (1995) Table 12.)

[GoneWest]

So at sea level - where h = zero - "the distance to the horizon d"...is zero??

Would you show that done for, say, five feet...the eye height of a man standing on the beach.

[henry crun]

The square root of 1½ times the height in feet will give an answer accurate enough for most purposes.

Height// Horizon in miles
5 == 2.7
20 == 5.5
50 == 8.7
100 == 12.3
500 == 27.4
1000 == 33.7
2000 == 54.8
5000 == 86.6
20,000 == 173.2

[ 19 December 2001: Message edited by: henry crun ]

[fantom]

it's bluddy miles away. <img src="rolleyes.gif" border="0">

[GonvilleBromhead]

Why would anyone wanna get there, you might fall off. Don't believe this new fangled 'science' malarky !

[vanman]

I've heard there're loads of well paid jobs going just beyond it....

[malanda]

I have a supplementary question: Several times I've heard it said that Concordes fly so high that you can see the curvature of the earth. (a) Is this true? (b) Does that extra 15,000-ish feet compared with 'normal' A/C make all the difference, and if so why?

[DownIn3Green]

Don't know why, but I'd bet it is true based on the fact that there is a very visible difference between FL350 and FL410, so it must get better as you go higher...

[Taff Missed]

Hey thanks guys. I was mulling this particular question over as I was driving home a few nights ago. Just how far away is that contrail on the horizon? 230-ish miles is the answer (assuming 35000ft). Thanks again.

Taff