The distance a person can see with the naked eye is limitless. So, if the phrase “as far as the eye can see” sounds like a long way, that’s because it is. But numerous factors affect the human vision range. To see a maximum distance, you’d need all circumstances to be optimal—such as a clear line of sight with nothing in the way, a tall vantage point, and a tall target.
We’ll take a look at these factors and others and explain how they help determine the human range of vision.
8 Factors Affecting How Far a Human Eye Can See
A lot of factors come into play when determining how far people can see.
For instance, on a clear, dark night, if a person with good eyesight has an unobstructed view, they can see the Andromeda Galaxy, around 2.5 million light-years away. The human eye can also see the Triangulum Galaxy. At around 3 million light-years away, it’s thought to be one of the farthest objects visible from Earth by the human eye.
However, we can’t always see millions of light years away. Certain circumstances tend to keep that from happening, such as obstructions, the particular viewing location, and the brightness of the distant object being looked at.
Let’s take a look at some common variables in the human range of vision.
1. Obstructions in the Line of Sight
Something usually blocks our view of the world in front of us, whether that’s a tree, a building, or a cloud. Tiny particles can also get in the way. For instance, air pollution can create a haze, which limits the clarity and color of what we look at. This shortens the distance we can see. Likewise, mist in the air on a humid day can reduce our range of vision, so we can’t see as far as we might on a clear day.
2. Curvature of the Earth
A person’s eyesight range on the ground depends on the curvature of the earth.
If a person stands on the ground and nothing blocks the view, they can see up to the horizon, which is around 3 miles into the distance. Because the earth is round, everything past the horizon line curves out of view.
3. Visual Acuity
A person’s visual acuity is an important factor in determining their range of vision. Visual acuity measures the sharpness of a person’s vision when looking at objects a certain distance away. In general, someone with better distance visual acuity will be able to see clearly farther than someone with worse distance visual acuity.
For instance, a visual acuity score of 20/20 means you can see at 20 feet what should normally be seen at that distance. But a visual acuity score of 20/100 means that you need to be at 20 feet to see an object someone with “normal vision” can see from 100 feet away.
Several factors can influence some people’s visual acuity, such as refractive errors, like myopia (nearsightedness) or astigmatism, or other vision conditions. People with these conditions may need corrective eyeglasses or contact lenses to help them see farther.
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The height from which you’re looking helps determine your range of vision. In general, the higher up you are, the farther you can see.
For example, the skydeck on top of the Willis Tower (formerly the Sears Tower) in Chicago is around 1,353 feet above the ground. It’s the highest public viewing spot in the United States. On a clear day, a person standing on the skydeck can see 40 to 50 miles into the distance. This is much farther than the 3 miles ahead one could potentially see from the ground!
5. Height of the Target (What’s Being Viewed)
The higher above the horizon an object is, the easier it is to see it from the ground. This is partially how it’s possible to see the Willis Tower, and other skyscrapers, from many miles away if the conditions are favorable.
6. Size of the Object
The size of the object being viewed needs to be taken into consideration as well. Generally, the bigger something is, the easier it is to see it from far away. With circumstances being equal, a large hot air balloon in the sky would be easier to see than a lost helium party balloon at the same distance.
7. Brightness of the Object
The brighter an object is, the easier it is to see it. For instance, we can usually see the sun quite easily, even though it’s around 93 million miles away. (Remember: sunlight can damage your eyes! Never look directly into the sun.)
But what about something smaller, like a lit candle? On a clear day, the farthest away a human eye can see a candle flame is approximately 1.6 miles in the distance.
8. Air Temperature
The temperature of the air has an impact on a human’s vision range. Cooler air and hotter air have different densities. Variations in air density cause light rays to bend differently when it passes through them. This effect is called atmospheric refraction. It can cause optical illusions, like objects above a radiator seeming to wave in the heat. Similar illusions, like a mirage of water on the road during a drive, can alter how accurately we are viewing distant objects.
Healthy Eyes Help You See Far
Even if you’re seeing clearly at all distances, getting regular eye exams will help you safeguard your eye health. Your eye doctor will not only check your vision but will check for any eye conditions and recommend treatment if needed.
