# What's the maximum distance one can see with the naked eye?

Like if you are on the ocean or any other completely flat surface, what's the maximum distance one can see?

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A tad over 3 miles, if your eyes are five feet off the ground. The calculation for distance to the horizon is 1.23 x the square root of the height of your eye.

Check out this site for different heights: http://www.boatsafe.com/tools/horizon.htm

Of course, something large or high (mountain, bird), you can see further away.

• Anonymous

Normally the naked eye can see stars with an apparent magnitude up to +6m; angular resolution of the naked eye is about 1′ however, some people have a sharper vision than that. Theoretically, at up to +6m the human eye would see about 2,500 stars in the clear sky but, in practice, the atmospheric extinction and dust reduce the number to 1500 to 2000 (in the center of a city as few as 200 to 500, due to light pollution). Colours can be seen but just at bright stars and the planets,Many other things can be estimated without an instrument. If an arm is stretched the span of the hand corresponds to an angle of 18 to 20°. The distance of a person, just covered up by the outstretched thumb, is about 600 meters. The vertical can be estimated to about 2°.

On earth u can see up to horizon approx. 200 km

• suitti
Lv 7

At night, from a fairly dark sky spot, it's fairly easy to pick out M31 - the Great Andromeda galaxy. That's 2.5 million light years away. And it's usually quoted as the farthest thing you can see naked eye. I've seen it.

However, there are reliable reports of other galaxies being spotted naked eye. The galaxy m81 (12 million light years away), and the galaxy m51 (23 million light years away) have also been spotted. To make this happen, people go to extremely dark skies, have excellent weather (no clouds, not turbulent, etc), and often stand on high mountains and the object in question is as high in the sky as possible. Sometimes, in order to improve vision from high mountains, a little extra oxygen is carried.

• Anonymous

2.5 million light years, to the andromeda galaxy.

you can calculate the horizon distance as easily as i can. but even the clouds may be farther away than that.