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HOW FAR CAN THE HUMAN EYE SEE...

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Suzuki
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PostPosted: 15:36 - 21 Nov 2006    Post subject: Reply with quote

depends how bright the light is you're looking at, and whether something gets in the way.

You can see the stars right, and the closest of them is 4 light years away.

Stupid question really, since the eye just detects light that hits it.

A better question would be "How far can light travel" Razz
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byke95
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PostPosted: 15:47 - 21 Nov 2006    Post subject: Reply with quote

I think there's an advert about that states that the human eye can see a candle from two miles away. However, this is a pretty useless 'fact' as it will be dependent on a number variables, as Suzuki mentioned.

What interests me more is 'how do I know what you see is the same as what I see?'. As humans we can only presume/guess (or theorise - the argument of analogy)
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tokarev
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PostPosted: 15:50 - 21 Nov 2006    Post subject: Reply with quote

Yep, it depends on the intensity of the light.

Who knows byke95, your green could be how I see my red?!! Could be possible but I am not too sure about it.
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Trixie
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PostPosted: 15:52 - 21 Nov 2006    Post subject: Reply with quote

On a clear day I can look across the water and see Cumbria/Scotland/Ireland (depending on which part of the coast I'm on). My guess is that they're an average of 20/30 miles away.

Great view, apart from Sellafield. Confused
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Rookie
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PostPosted: 16:15 - 21 Nov 2006    Post subject: Reply with quote

If I remember rightly the farthest star from us viewable by the naked eye is about 7,700 light years away.
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dainesefreak
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PostPosted: 16:43 - 21 Nov 2006    Post subject: Reply with quote

Suzuki wrote:
A better question would be "How far can light travel" Razz


And how does it get there? Wink
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ken
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PostPosted: 16:49 - 21 Nov 2006    Post subject: Reply with quote

I think the sun is 90+ milion miles away and I can see that

does that help
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Suzuki
Roger



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PostPosted: 16:51 - 21 Nov 2006    Post subject: Reply with quote

ken wrote:
I think the sun is 90+ milion miles away and I can see that

93 million miles to be a little more precise, although the distance changes through the earth's orbit. Smile
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Black Knight
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PostPosted: 17:04 - 21 Nov 2006    Post subject: Reply with quote

I can't see my toes Embarassed
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akaDAVE
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PostPosted: 17:41 - 21 Nov 2006    Post subject: Reply with quote

A bit of a sidetrack to this thread but I've always wondered why so many people have to wear glasses/contact lenses.
We seem to be very well evolved as humans and eyesight is our primary sense so why are there so many short sighted humans around?
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TheShaggyDA
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PostPosted: 17:46 - 21 Nov 2006    Post subject: Reply with quote

Probably because we spend too much time looking at things too close. In order to have good distance vision, the eye needs to relax. The muscles come into effect bringing the focus closer. Once you start school and spend hours looking at stuff from 1ft-20ft away, the eye just gets used to it, and can no longer return to the fully relaxed position.
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Walloper
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PostPosted: 17:50 - 21 Nov 2006    Post subject: Reply with quote

I can see to the end of my kno@....
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oldpink
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PostPosted: 17:59 - 21 Nov 2006    Post subject: Reply with quote

whats the speed of dark Rolling Eyes
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The View Askew
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PostPosted: 18:49 - 21 Nov 2006    Post subject: Reply with quote

oldpink wrote:
whats the speed of dark Rolling Eyes


Same as the retreat of light.
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G
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PostPosted: 19:31 - 21 Nov 2006    Post subject: Reply with quote

akaDAVE wrote:

We seem to be very well evolved as humans and eyesight is our primary sense so why are there so many short sighted humans around?

Because natural selection means that those that are short sighted learn to work around it - IE we run and hide when we see the big fuzzy thing coming, regardless of if it's a cloud or a mammoth Razz.

In today's modern world it can also be beneficial - I can print off an A5 document at 25 pages per side on A4 and still read it - saving time and money Razz.
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Finglonga
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PostPosted: 20:34 - 21 Nov 2006    Post subject: Reply with quote

byke95 wrote:
I think there's an advert about that states that the human eye can see a candle from two miles away. However, this is a pretty useless 'fact' as it will be dependent on a number variables, as Suzuki mentioned.


I take it thats at night? Also you wouldn't see shit if some fucker forgot to light it. Wink
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G
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PostPosted: 20:54 - 21 Nov 2006    Post subject: Reply with quote

https://www.dimaggio.org/Armagh/Planetarium/Armagh/images/Maynooth/Mvc-54x7f.jpg

At almost 3.5m tall you could probably see it from a way away in day light Wink - and apparantly there has also been one made getting close to 5.5m; which would burn for about 1800 days they say, so you'd at least have a chance to walk up to it if you couldn't see it from 2 miles away Smile.
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Finglonga
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PostPosted: 21:31 - 21 Nov 2006    Post subject: Reply with quote

Er...........Looks like its made from ear wax?!?! Sick
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hellkat
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PostPosted: 21:56 - 21 Nov 2006    Post subject: Reply with quote

I dunno about candles and stuff, but I have to hold things further away from me to read small print these days.

hellkat
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Teaman
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PostPosted: 22:43 - 21 Nov 2006    Post subject: Reply with quote

Walloper wrote:
I can see to the end of my kno@....


You must be very short sighted Smile



NERD ALERT
Question:
How far apart, assuming no obstacles, can two people stand and still see each other?

i know this deals with the curvature of earth, but i can't figure out the formulas involved.

thanks!




In the diagram below r is the radius of the earth, approximately 3963 miles, and h is the height, in feet, of a person standing in the surface of the earth, and C is the center of the earth.

https://mathcentral.uregina.ca/QQ/database/QQ.09.03/judy1.1.gif
First notice that the height of the person in miles is h/5280. The line segment AB is the line of sight of this person to the horizon. Since AB is tangent to the circle, the angle CBA is a right angle. Thus, using Pythagoras' theorem, the length of AB is given by
sqrt[(r + h/5280)2 - r2]
But
(r + h/5280)2 - r2 = (r + h/5280 - r)(r + h/5280 + r) = h/5280(2r + h/5280)
h/5280 is much smaller then 2r, hence 2r + h/5280 is approximately 2r and thus
(r + h/5280)2 - r2 is approximately 2rh/5280
Substituting r = 3963 miles give the neat result that if your eyes are h feet above the earth, then the distance to the horizon IN MILES is about
sqrt( 3*h/2) miles.

Thus a person 6 feet tall standing on level ground can see for about 3 miles. So, theoretically, a person 6' tall (with binoculars) should be able to see the top of the head of a six-footer who is 6 miles away. He would see the whole person at a distance of 3 miles.
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hellkat
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PostPosted: 22:46 - 21 Nov 2006    Post subject: Reply with quote

Ack.
Physics Sick

*chunders*
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G
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PostPosted: 22:49 - 21 Nov 2006    Post subject: Reply with quote

Teaman wrote:

i know this deals with the curvature of earth, but i can't figure out the formulas involved.

Indeed, the people could be standing on two high mountains with a clear line of sight Smile.
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Ahmato_
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PostPosted: 22:50 - 21 Nov 2006    Post subject: Reply with quote

Hey Teaman, I'm gonna show my dad that and see what he says. He'll proberbly start nodding and grumbling quietly to himself on how maths isn't what it was Thumbs Up Mr. Green
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Teaman
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PostPosted: 22:58 - 21 Nov 2006    Post subject: Reply with quote

i quoted it Smile


I havn't the foggiest what it means


I was lead to believe its relative to how high you are,
If your at sea level you have the curature of the earth so I think thats 5 miles ?

if its higher up you dont so its further, (being able to see france from england on a clear day and so on)
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There is no point in ranting about someone stupid because there is nothing u can do about it. There is no cure for stupid.
Someone stupid does not realise they r stupid.stupidity is indistinguishable from malice U just have to accept that some people are thick as p1gsh1t and work around them.
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