How far can your eyes see?

Visual acuity refers to your eyes' ability to see things — specifically to accurately distinguish shapes at various distances. When people talk about visual acuity, they usually mean practical considerations. Can someone see well enough to drive? Is their visual acuity accurate enough at close distances to read?

But you might also wonder, "How far can the human eye see?" This scientific question brings up many fun considerations, and we'll explore some below.

How far can the human eye see?

If you can pick out stars in the sky, you're seeing light that's traveled from 2.5 million light-years away. That's millions of trillions of miles away. Technically, that's how far a human eye can see.

Considering what we can see in the night sky without the help of a telescope is fun, but it's not exactly practical. Unless you're a professional or amateur astronomer, you might not be that interested in whether you can see far enough to pick out the Andromeda Galaxy in the dark night.  

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How far can the human eye see in miles on Earth?

This is certainly a more practical consideration for most people. If you stand on the earth, how far away can your eyes see? Turns out, the answer depends on a variety of factors, including whether your view is obstructed (of course), the brightness of what you’re looking at and the overall conditions around you.

But aside from all that, if you're standing somewhere on Earth that's relatively flat, you may be able to see a total of 2.9 miles away. That's how far you can see before the curvature of the Earth gets in your way.

Imagine that you climb a mountain or go to the top of a high building. If your view from the top of these structures isn't obstructed by anything else, you can see further than 2.9 miles. That's because you're high enough that it takes a longer distance before the curvature of the planet gets in the way of your field of vision.

Interestingly, temperature also has a big impact on how far you can see. Typically, you can see farther away on a cool, clear day than on a hot, clear day.

What is the farthest anyone has ever seen on Earth?

In July 2016, Mark Bret took a photograph that captured the Guinness World Record for the longest line of sight ever recorded. That record still stands today, and it's 275 miles. He took the photograph that demonstrated the line of sight from high in the Pyrenees mountains in France. In the image, you can see specific mountains in the Alps, which are 275 miles away.

What if your eyes don't see that far?

Of course, not every naked eye has the same capability, and many people can't see anything that's 275 miles — or even 275 meters — away with any clarity at all. Modern vision correction products, such as contacts, can solve most of these challenges, though. Browse contacts at 1-800 Contacts to maximize your visual acuity, whether you're viewing Earth from the mountaintops or just want to see across the grocery store correctly. You can also take our free online ExpressExam to renew your contacts prescription.