how far can the human eye see over land?

Question

if you were to look across a flat plain,how for could the human eye see before the curvature of the earth made it disapear

Answer 1

Distance to horizon = 3.56*sqrt(h) km
where h is the height of the observer's eyeline above the surface (in metres).

This means the average person can see about 4.5 km.

Answer 2

Why is the 'best answer' rated to the answer that did not answer the question. the Asker if you read the question again asked "What I want to know is on a flat surface looking straight ahead (the surface remaining flat the entire distance)" The Asker did not want to know about the curvature of the earth. This question did not exist. The question does not ask about how far can the eye see on a curving surface. The asker stated 'a flat surface' Since when in mathematics do we mix up a flat surface with a curved surface. You have turned a very simple question in to a complicated question by introducing a curved plane. And why have you assumed the plane is curving downwards? why not curving upwards? So you have changed the question now to mean the Asker is wanting to know the maximum distance on a curved surface, and the surface curving downwards. This information was given in the original question. The original question specified only a perfectly flat surface.

Answer 3

The stars are light years away, everyone who isn't blind can see them.
When approaching a city with a well known land mark, the land mark can be seen from miles away, depending on the land marks height and whether there is a clear uninterrupted view or not.
At the coast ships miles out at sea can be seen.
The French coast can be seen from the cliffs of dover in England, a distance of about 22 miles.
Mountain ranges can be seen from even greater distances.

Answer 4

Apparently 7 Miles.

Answer 5

I have thought about this myself, it would come down to question of height for persons eye from ground level, assuming then a right angle and an accurate enough mark this then could be worked using Pythagorus, but I can't work out how to amke the accurate mark to form the hypotenuse of the triangle, good question though have a star

Answer 6

I read in some nautical novel, the horizon presented was about 18 miles to the observer on deck.

But, I researched. The link shows some math formulas putting the average at 3.10 miles.

Answer 7

in complete darkness with no obsticles, and no light polution a candle can been seen from 14 miles away. If yo were in an areoplane you would see the curviture of the earth at 50.000 ft stainless

Answer 8

Worked out using pythagoras.

Distance to horizon =
Square root of (h^2 + 2rh)
Where units are Km and
r=6366 (radius of Earth)
h = Your eye height above sea level (or in this case the ground)
So if your eyes are 1.5m above sea level / ground
h=1.5/1000

Works out like this:

For
h=1.5m Dist = 4.4 Km
h=5m Dist = 8 Km
h=10m Dist = 11.3Km
h=20m Dist = 16 Km
h=30m Dist = 19.5 Km

Answer 9

I have often thought this when at crusing altitude (say 38,000 feet) looking out the window of a plane. Im sure there is a formula somewhere that tells you. I would be interested to know though

Answer 10

we can see for miles
infact when we were being invaded people alerted each other by lighting flames on towers from the coast line up to main cities and the distance between was anything from 5 to ten miles