Hi, I'm Craig and I have eyes like a hawk with human eyes, and this is Mental_floss on YouTube. Today I am going to answer Brian Currie's big question "On a clear day how many miles can I see in every direction? how about on a hazy day?"

Well, Brian, the answer to your question really depends on the circumstances. Like some nights you can look up at the sky and see the Andromeda galaxy  which is a full 2.5 million light years away, but you probably want more information than that, so that's what you are going to get. Maybe you don't want more but we like to talk about stuff at you, so we are going to do that. Let's get started.

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According to a study done in 1942, the human eye can actually see a single flame burning 30 miles away, that's around 50 kilometers, but that can only happen if the earth were flat. The Earth ain't flat. we can actually see much further than we do see, it's that darn horizon that gets in the way. The horizon, by the way is where the earth meets the sky, you've heard of it, you've seen it, on Instagram.

So if that's the case, you've probably figured out the altitude has an impact on how far you can see. So, if you are an average height of 5 foot 7 inches and standing on the ground the horizon is approximately 2.9 miles away.

So people can see 2.9 miles away. Boom, Done. No, unfortunately it is not that simple; humans can't come up with a simple formula that works for every situation. And that's because we have things like atmospheric refraction, which is how light passes through different mediums in different ways. Thanks to that, things like air pressure and temperature are actually affecting the way you see the horizon.

Also that big guy at the top of the Sears tower when you are trying to look out the window, but he just won't get out of the way. You paid twenty buck to get up there. Then of course as Brian so astutely mentioned there are factors like haziness and fog.

If you wanted to see really far you could hop on a plane or climb Mount Everest, but then you will probably have a cloud get in your way.

All of that said, Dr. Andrew T. Young, who I will call young Mr. T of San Diego State University has developed this formula that takes refraction into consideration. All you gotta do is insert your eye level in feet, and it will give you an approximation of your distance to the horizon in miles. But like I said, no formula you find for this will be perfect, there are just too many variables.

If all this confusing refraction stuff is too much for you, you can just calculate how many miles there are between you and the horizon. there is a link in the dooblydoo for an online calculator that will dooblydoo the work for you.

Heh, puns.

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Thanks for watching Mental_floss here on YouTube, made by these lovely people. If you have a question of your own leave it in the comments. See you next week, from an average distance.