# Can I believe my eyes?April 9, 2009 7:39 PM   Subscribe

Can I really see buildings up to 40 km away?

The buildings themselves are 36 m and 83 m high, and stand on a hill about 50 m above sea level. The times when I've seen them I have been between 35 and 40 km away, at a height of about 60 to 90 m above sea level. The land between is very flat, and there is little but low rise houses and trees between us.

I've several times caught sight of these buildings (often the larger one only) when I've been walking, but the person I've been with hasn't been able to see them. Anybody I tell says that I'm much too far away to sight them, but the other day I was lucky enough to be carrying a camera, and so took this picture. Obviously I used the zoom to take this picture, but it shows exactly what I can make out on the horizon.

Please tell me I'm right and everybody else is just hard of sight!
posted by Sova to Science & Nature (21 answers total) 1 user marked this as a favorite

Yes. This example at wikipedia says that you could probably still see them (barely) even at the bottom of the hill you're on (the numbers roughly line up...100m tower visible from eye height over a distance of 35km).
posted by cowbellemoo at 7:57 PM on April 9, 2009

Judging from the picture, it looks like something I'd have no trouble seeing on the horizon. I haven't had my eyes checked in a long, time, but I consider myself to have perfect vision.
posted by zsazsa at 7:58 PM on April 9, 2009

Best answer: As this article explains, it's a function of how high above the ground you are. That, and how hazy/cloudy/foggy it is.

Given your numbers, it all seems to fit.
posted by JuiceBoxHero at 8:02 PM on April 9, 2009

Best answer: According to wikipedia, the formula for distance to the horizon is: sqrt(13h) where h - height above sea level in meters.

Plugging in 90m above sea level, which is the maximum height you gave, the horizon would be approximately 34km away. Given that the buildings have a height of their own, it's certainly plausible that you can see them, as long as the air is clear enough.
posted by chrisamiller at 8:03 PM on April 9, 2009

You can easily make out structures in the trees (if you know precisely where to look) on the other side of the Grand Canyon, which is 16km wide at the point that structures exist. The widest point is 29km across, and you can still make out bands of rock with no problem. Granted the Grand Canyon area is unusually clear, but it suggests that you are indeed, seeing those distant buildings.
posted by notsnot at 8:37 PM on April 9, 2009

Plugging in 90m above sea level, which is the maximum height you gave, the horizon would be approximately 34km away. Given that the buildings have a height of their own, it's certainly plausible that you can see them, as long as the air is clear enough.

To account for the height of the buildings themselves, you just have to have the horizon as seen from the top of the buildings "overlap" with your own horizon. The horizon as seen from the top of the shorter building has a radius of 33 km on its own, so it's well within your field of view even if the base of the hill it's on might not be.
posted by Johnny Assay at 8:42 PM on April 9, 2009

Absolutely. As part of a volunteer gig I do, I have to know how far certain landmarks are from where I'm observing, and some of them are 60 miles (96 km) away.
posted by rtha at 8:50 PM on April 9, 2009

In rare cases, you can get a superior mirage. That is, an image of something that is actually below the horizon. I don't think that's what happened here, though. I think you can just see the buildings from where you're standing.
posted by Cool Papa Bell at 8:54 PM on April 9, 2009

Yep, you definitely can. From St. Catharines, you can see downtown Toronto across the lake (not just the CN Tower) and it's more than 40 Km. There's some elevation on both sides, but not that much.
posted by Dipsomaniac at 9:04 PM on April 9, 2009 [2 favorites]

Anecdotal datapoint: I've seen the skyline of Dallas from about 25 miles away (around 40 km) in Plano, from a second story window. Those buildings are all over 200 meters tall, but are also more clearly visible than the buildings in your photo. This is on a clear day over very flat terrain, but with more in the way than in your case.
posted by MadamM at 9:39 PM on April 9, 2009

You can probably see them better indirectly, from the corner of your eye, than straight on. This may be what is befuddling your companion.
posted by rokusan at 10:54 PM on April 9, 2009

This picture shows the skyline of Chicago from the Indiana Dunes State Park. Straight line distance from where I took the photo to the Sears Tower is 32.5 miles, or over 53 kilometers as measured in Google Earth.
posted by pjern at 1:26 AM on April 10, 2009

This sort of thing happens with me and my wife all the time. She'll see something in the distance and point it out to me, and I see nothing. I'd assume she must be making it up or imagining it or something, but, of course, there's no reason for her do so, and it's happened with such regularity and specificity that it must be true--her eyes are just better than mine for such things.
posted by MrMoonPie at 6:32 AM on April 10, 2009

Seconding the downtown Toronto. From certain points on the Niagara Escarpment (near Lockport, NY) I can see lots of downtown Toronto.
posted by jdfan at 7:16 AM on April 10, 2009

Downtown Toronto at a distance of 50 km, as the nautical crow flies.
posted by DrJohnEvans at 8:37 AM on April 10, 2009

Haha, I was going to come and chime in about seeing Toronto from over 40 k away on the escarpment too. And my eyes are REALLY, REALLY bad.
posted by saucysault at 8:43 AM on April 10, 2009

Response by poster: Thanks everybody! Definitely going to spend the time looking for landmarks even further away next clear day I get!
posted by Sova at 9:07 AM on April 10, 2009

I too have seen Chicago from Michigan City, Indiana, as in pjern's picture.
posted by IndigoRain at 1:04 PM on April 10, 2009

Can't match Toronto, but on a clear day in SF you can see the Farallon Islands, 43km offshore.
posted by rdc at 10:39 PM on April 10, 2009

I heard on the BBC shipping forecast two nights ago that visibility from one of the northern Scottish coastal stations was 39 miles. That is about 62 km. I was surprised, so your 40km buildings seem completely plausible.
posted by multivalent at 4:08 AM on April 11, 2009

The other thing to take into account is the resolution of the eye - the average eye can distinguish features of about 1 arcminute, which equals about 12m at a distance 40km. So it's entirely reasonable to be able to see those buildings.
posted by Electric Dragon at 1:06 PM on April 28, 2009

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