There is no practical limit to how far the naked human eye can see. The human range of vision is infinite. However, several factors affect the distance you can see. The human eye can see objects at any distance provided they are bright enough and there are no obstructions in between. It is for this reason that you can see stars and galaxies that are hundreds or thousands of light-years away.
Factors That Affect How Far You See
For an unobstructed view, the farthest object an unaided keen human eye can see is The Triangulum Galaxy (Meisser 33). The galaxy is located about 3 million light-years away from Earth and can be seen under clear and dark skies. The many bright stars in the galaxy produce enough light for photons to excite your retina.
On a global scale, you can see up to about three miles (five kilometers) before the horizon becomes the limit because of the earth’s curvature. From a high vantage point, like a skyscraper, plane or mountain top, your eyes can see objects hundreds of miles away.
The biggest factors in how far you can see are your overall eye health, the brilliance of the objects you are looking at, the curvature of the earth and the existence of any obstructions in your line of sight.
Your Overall Eye Health
The health and function of your eyes are central factors that determine how far you see. A person with good eye health will have better eyesight than one with poor eye health.
Size and Brightness
Bigger objects are easier to see at a distance since more light bounces off the objects. However, the brightness of an object also plays a part. Brighter objects produce a higher number of photons, making them easier to see at a distance. This is why you can see the sun and other stars when they are millions or billions of miles away.
The earth curvature interrupts your line of sight. As such, the farthest edge you can see standing on a flat surface is about 3 miles away. If your vantage point is higher off the ground, the horizon edge gets a lot further away. The earth’s curvature doesn’t cut off objects from your light of sight as soon.
Obstructions in Your Sight Line
Your sightline is the uninterrupted visual angle from your eyes to the object you’re trying to see. Any obstructions in your light of sight will affect how far you can see. Obstructions may include dust, smoke, water vapor, fog, and clouds.
Visual acuity is your eye’s ability to distinguish details of objects (clarity of vision) at a given distance. Your visual acuity plays an important role in how far you can see. Health care professionals consider a 20/20 vision to be a normal healthy vision.
Having 20/20 vision means you can clearly see an object 20 feet away that you should be able to see at that distance. People with better visual acuity can see objects at a distance more clearly.
For instance, if you have 20/80 vision, you can see an object clearly at 20 feet, that a person with 20/20 vision can see clearly from 80 feet.
Meisser 33 (The Triangulum Galaxy). (February 20, 2019). National Aeronautics and Space Administration.
How far can the human eye see? (May 7, 2012). LiveScience.
How Far Can The Human Eye See. (n.d). Optical Academy.
What are the limits of human vision? (July 27, 2015). The British Broadcasting Corporation.
Evaluation of Visual Acuity. (February 21, 2022). StatPearls.
Last Updated July 1, 2022
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