How far away can the human eye see?

Answer 1

The human eye can easily see the Magelannic clouds, which are some 200, 000 light years away.

Answer 2

How far can you see?

It is of interest to consider how far the eye can see under different conditions. Usually the visibility is limited by scattered light in the lower atmosphere. Even under extremely clear conditions, it's unusual to see more than a couple of hundred kilometers.

However, there is one situation in which objects can be made out at great distances: when they are silhouetted against a bright background, such as the setting Sun, or (just after sunset) a bright twilit sky.

The record for seeing a distant mountain against the Sun appears to be the observation of a Japanese mountain at a distance of 1177 km, seen at sunrise from a ship in the Sea of Japan.

What's the record for visibility without help from the silhouetting effect? It belongs to the report of the expedition led by Korzenewsky (1923), who reliably reported seeing snow-capped peaks of a mountain range 750 km away. Conditions were perfect: the lower atmosphere was in shadow at sunset; the peaks were quite high (4650 meters, or over 15,000 feet); they were covered with white snow, increasing their visibility; and there must also have been considerable looming to bring these distant features above the observers' horizon.

For less extreme, but reliable, observations, consider some listed by Commander C. L. Garner of the Coast and Geodetic Survey in 1933. He says that instrumental measurements were made in both directions “between Mt. Shasta and Mt. St. Helena in California, a distance of 192 miles.” [That's 309 km.] Apparently this was done in normal conditions, with no looming; heliotropes having 12-inch [30-cm] mirrors were used. He also credits the 1911 sighting of the Fairweather Mountains in Alaska from the ship Explorer from the Gulf of Alaska, 330 miles [531 km] away.

http://mintaka.sdsu.edu/GF/explain/atmos_refr/horizon.html

Answer 3

Cycles per degree (CPD) measures how much an eye can differentiate one object from another in terms of degree angles. It is essentially no different from angular resolution. To measure CPD, first draw a series of black and white lines of equal width on a grid (similar to a bar code). Next, place the observer at a distance such that the sides of the grid appear one degree apart. If the grid is 1 meter away, then the grid should be about 8.7 millimeters wide. Finally, increase the number of lines and decrease the width of each line until the grid appears as a solid grey block. In one degree, a human would not be able to distinguish more than about 12 lines without the lines blurring together. So a human can resolve distances of about 0.93 millimeters at a distance of one meter. A horse can resolve about 17 CPD (0.66 mm at 1 m) and a rat can resolve about 1 CPD (8.7 mm at 1 m).

A diopter is the unit of measure of focus.

Answer 4

I don't think it can really be measured, because when you look out at water, or land, your eye reaches the horizon line, and beyond that, it's just sky- and you really can't tell how far into the sky you're seeing. I'd imagine that if the horizon line didn't exist, and there was nothing to get in the way, the human eye could see nearly forever.

Answer 5

In the sky, it is as far as an object emits or reflects light that come to our eyes. But in the ground surface the distance to horizon depends on height of the observer (man). There is a mathematical formula, but at this moment i am unable to provide the formula, later i can.

Answer 6

As far as we want until something obstructs our view or the horizon causes everything to disappear but the sky. That is why it is stupid to think that in medievel times everyone thought the world was flat. Most thinking people knew better. Even so, we still have among us members of the Flat Earth Society.

Answer 7

The most distant object visible to the unaided human eye is the Andromeda Galaxy (M31). It's about 2.2-million light years away from Earth.

Answer 8

Yeah, I was thinking in terms of feet..or yards...But when You folks start mentioning space, I havent an idea. You are not actually seeing the object, but light emiting from that object. Anyway, I'll guess about 1/2 mile.

Answer 9

the human eye can see for 550 yars but the depth perception will be very poor. the eye can see 1500 feet and can still tell the depth preception

Answer 10

I guess it depends on what you are looking for:

A grain of rice - maybe 10- 15 feet away.

A mountain -- 100 miles or more away.