WEBVTT - How Far Can the Human Eye See?

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<v Speaker 1>Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff, Lauren Fogelbaum. Here.

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<v Speaker 1>You may not spend a lot of time staring off

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<v Speaker 1>toward the horizon trying to make out distant objects, But

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<v Speaker 1>if you do, how far would be possible for you

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<v Speaker 1>to see? Pretty far, as it turns out, if you're

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<v Speaker 1>a person with normal visual acuity a rating of twenty twenty,

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<v Speaker 1>and you gaze out in a horizontal line from around

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<v Speaker 1>five feet or one and a half meters above the ground,

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<v Speaker 1>you can see for about three miles or five kilometers

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<v Speaker 1>into the distance, which is the point at which Earth's

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<v Speaker 1>curvature bends away so that the surface is no longer

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<v Speaker 1>in view. And while your ability to discern objects depends

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<v Speaker 1>upon their size and how much light the distant object

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<v Speaker 1>emits or reflects on a dark night, it's possible to

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<v Speaker 1>see a single candle flame from about one and a

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<v Speaker 1>half miles or two and a half kilometers away. To

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<v Speaker 1>understand how our eyes can see a distant object like

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<v Speaker 1>a candle flame flickering, it helps to know something about

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<v Speaker 1>how normal vision and the human eye work. A While

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<v Speaker 1>visual acuity varies among individuals, the naked eye is definitely

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<v Speaker 1>an impressive piece of equipment. It's capable of twelve times

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<v Speaker 1>the resolution of a high end smartphone's camera. We can

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<v Speaker 1>perceive a nearly infinite range of colors and shapes, as

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<v Speaker 1>will as detect very small changes in brightness and minute

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<v Speaker 1>amounts of motion. Human vision is a complex, intricate process.

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<v Speaker 1>A light emits from or reflects off of objects, and

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<v Speaker 1>then passes through the cornea and the lens of the eye,

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<v Speaker 1>a which bend and focus light onto the retina at

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<v Speaker 1>the back of the eye. There a layer of tiny

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<v Speaker 1>nerve cells called rods and cones are activated by the

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<v Speaker 1>light and send electrical impulses through the optic nerve to

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<v Speaker 1>your brain, which creates an image or visual perception. For

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<v Speaker 1>the article, this episode is based on How Stuff Works.

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<v Speaker 1>Spoke with doctor Eric Lowell Singhman, a practicing optomologist with

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<v Speaker 1>the University of Maryland Medical System and the Professor of

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<v Speaker 1>Optomology with the University of Maryland School of Medicine. He said,

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<v Speaker 1>the eye turns light into biometric energy transmitted to the brain.

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<v Speaker 1>Some nerve cells see colors, some see black and white,

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<v Speaker 1>Some see motion only in one direction, others see motion

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<v Speaker 1>in another. Direction, some see shapes, some just look at

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<v Speaker 1>the overall ambient lighting. Together, those cells work as a

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<v Speaker 1>team to tell your brain what to visualize, a transmitting

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<v Speaker 1>information about what's moving and what colors things are. The

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<v Speaker 1>singman said, these are actually different, separate channels, and then

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<v Speaker 1>your brain takes the images and converts them into something

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<v Speaker 1>that your conscious mind can appreciate. In addition, the human

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<v Speaker 1>visual system also transmits and creates visual information that you

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<v Speaker 1>you aren't even necessarily aware of, for example, the amount

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<v Speaker 1>of ambient light, which helps control your natural rhythms of

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<v Speaker 1>day and night. Without obstructions in the way, you can

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<v Speaker 1>see about three miles where five kilometers into the distance

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<v Speaker 1>from ground level before you reach the point where earth

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<v Speaker 1>curves enough to block your view of what's on the ground.

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<v Speaker 1>But that's based on a hypothetical person who's five feet

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<v Speaker 1>or one and a half meters tall. If you're taller,

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<v Speaker 1>you could see farther based just on your angle of sight. Similarly,

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<v Speaker 1>the higher you go in elevation, the farther into the

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<v Speaker 1>distance you can see. A person looking out from the

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<v Speaker 1>observation deck of the world's tallest building eight hundred and

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<v Speaker 1>twenty eight meters skyscraper in Dubai that's about twenty seven

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<v Speaker 1>hundred and seventeen feet. Reportedly can see for sixty miles

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<v Speaker 1>or about one hundred kilometers, and our visual acuity extends

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<v Speaker 1>beyond the horizon. Even if the curvature of the Earth

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<v Speaker 1>didn't exist, and instead Earth was a flat surface, would

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<v Speaker 1>have an uninterrupted visual angle from our eyes to the

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<v Speaker 1>farthest object visible. This is evidenced by the fact that

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<v Speaker 1>we can see extremely distant objects in space. As long

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<v Speaker 1>as the sky is clear and the object is bright

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<v Speaker 1>enough on a dark night without light pollution, you should

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<v Speaker 1>be able to see the Andromeda galaxy, which is two

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<v Speaker 1>point five million light years away. That's the equivalent of

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<v Speaker 1>fifteen quintillion miles or twenty four quintillion kilometers on Earth.

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<v Speaker 1>Our atmosphere is also a major factor in how well

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<v Speaker 1>you can see distant objects. Theoretically, in a vacuum, there's

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<v Speaker 1>no limit to how far away your eyes could see,

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<v Speaker 1>since light rays can travel an infinite distance. But even

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<v Speaker 1>though our air seems insubstantial, it actually contains a lot

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<v Speaker 1>of stuff. Houstuffworks. Also spoke with doctor Timothy McCully, a

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<v Speaker 1>professor and chair in the Department of Optomology and Visual

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<v Speaker 1>Science with McGovern Medical School at UT Health Houston explained,

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<v Speaker 1>you're seeing through the atmosphere and yellow particular matter in

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<v Speaker 1>the air is scattering the light. So depending on the

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<v Speaker 1>medium that the light is traveling through, those electromagnetic waves

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<v Speaker 1>will or will not reach your eyes. A similar problem

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<v Speaker 1>occurs on a foggy day or night, or during rain

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<v Speaker 1>or snow. That's why we're able to see that candle

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<v Speaker 1>flame flickering a long way off when there's a dark,

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<v Speaker 1>clear night sky, but not when the light is impeded

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<v Speaker 1>by precipitation, even though we can see a glowing object

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<v Speaker 1>far in the distance. The human eye does have its limitations,

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<v Speaker 1>especially when it comes to visual acuity, which is the

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<v Speaker 1>scientific term for sharpness of vision. Our cone cells, the

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<v Speaker 1>photoreceptors that are sensitive to red, green, and blue wavelengths

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<v Speaker 1>of light, are concentrated in the macula, an area in

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<v Speaker 1>the middle of the retina. Our sharpest vision is at

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<v Speaker 1>the center of the macula, in a spot called the

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<v Speaker 1>phobia that can zero in on a small part of

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<v Speaker 1>the world in front of you. A singmund said, you

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<v Speaker 1>might think that you have a very wide visual field,

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<v Speaker 1>but the reality is that your area of clearest vision

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<v Speaker 1>is actually just a few degrees. You don't see the

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<v Speaker 1>whole world clearly. If you take a big letter, eat

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<v Speaker 1>a big as your hand and move it about fifteen

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<v Speaker 1>to twenty degrees away to the side, you wouldn't be

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<v Speaker 1>able to tell what that letter was. The clarity of

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<v Speaker 1>your vision drops pretty quickly once you get off center.

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<v Speaker 1>That's why macular degeneration and eye condition in which the

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<v Speaker 1>macula becomes damaged so that you lose that central vision,

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<v Speaker 1>can be such a serious problem for people who get it.

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<v Speaker 1>The risk increases as you get older. But your eyes

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<v Speaker 1>are only part of the equation. That's evident in people

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<v Speaker 1>who have some sort of brain injury that interferes with

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<v Speaker 1>their vision, even if there's nothing wrong with their eyes.

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<v Speaker 1>Singmund said, you've got to remember that the brain is

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<v Speaker 1>a really big part of this process. There are types

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<v Speaker 1>of brain damage where you can't see something move, or

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<v Speaker 1>where you can't recognize faces. You'll look and pick out

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<v Speaker 1>an eye or a nose or mouth instead of the

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<v Speaker 1>whole face. The brain can also perform tricks to make

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<v Speaker 1>up for the eye's shortcomings. Singmann recalls the case of

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<v Speaker 1>a patient who, after eye surgery, suddenly discovered that when

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<v Speaker 1>he covered that eye, he couldn't see out of the

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<v Speaker 1>other but supposedly good eye. When a doctor examined the patient,

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<v Speaker 1>it was discovered that he had a cataract, a natural

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<v Speaker 1>clouding of the lens on that eye, but apparently had

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<v Speaker 1>never noticed it because of his brain's ability to filter

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<v Speaker 1>out the blur. Missingman said, that's a classic trick. The

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<v Speaker 1>brain can shut things off. Today's episode is based on

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<v Speaker 1>an article how far can the human Eye see? On

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<v Speaker 1>how stuffworks dot com written by Patrick J. Kiger. Brain

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<v Speaker 1>Stuff is production by Heart Radio in partnership with how

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<v Speaker 1>stuffworks dot Com and is produced by Tyler Klang. Four

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<v Speaker 1>more podcasts from my heart Radio, visit the iHeartRadio app podcasts,

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<v Speaker 1>or wherever you listen to your favorite shows. M