Hacker News
3 years ago by cs702

I've seen this optical illusion in person, with large container ships, off the US Mid-Atlantic coast, and it's really cool.

The photo in this article is fantastic. It shows an extreme example of the illusion. The ship appears to be, not just hovering over the water, but actually suspended in mid-air.

In my view, it's worth clicking on the link just to see the photo.

3 years ago by globular-toast

Something just occurred to me. Is this actually an optical illusion? My idea of an optical illusion is one where your brain perceives something that is different from reality. Indeed, when I look it up I see examples of that (e.g. https://en.wikipedia.org/wiki/Optical_illusion) But in this case your brain isn't doing anything wrong, the light reaching your eyes is what's "wrong" and your brain is correctly interpreting what your eyes see (as shown by the photograph).

3 years ago by red_trumpet

The Wikipedia article contains a helpful table [1], which classifies optical illusions. One kind are "physical" illusions, like rainbows or distortions (think stick in water). I think the hovering ship is of that kind. Other kinds include "physiological" or "cognitive", which are tricking your brain.

[1] https://en.wikipedia.org/wiki/Optical_illusion#/media/File:G...

3 years ago by unloco

This is a false horizon.

Your eyes are seeing the reflection of the sky on the distant water or fog, making it appear the horizon is closer than it really is.

So it is an optical illusion, as your brain is what is perceiving a horizon where it is not.

3 years ago by rixed

What you describe here is the usual kind of mirage, the one you see when light travels over a hot surface (desert sand, road) during summer.

This particular kind of mirage ("superior mirage", as the author of the picture calls it) works the other way around: light bends away from the cold water surface. So, of I understand it correctly, the horizon appears where it really is whereas the ship appears higher up (contrary to normal mirage where the sky appears to come from the ground).

3 years ago by russianbandit

It’s not just one person’s brain, right? Everyone who was there would see the same thing. Surely, that means our brains are pretty much wired the same. But I wonder if some people would see the “correct” thing.

What’s also mind blowing is that the camera captures the same thing your brain is interpreting!

3 years ago by Naracion

For what it's worth, the meteorologist specifically called it a mirage, not an optical illusion. Specifically, this is a "superior" mirage, meaning that the object appears to be above its actual location.

A mirage is not an optical illusion in the way that you describe it. The BBC correspondent is the person that called it an optical illusion, not the meteorologist. :)

3 years ago by LegitShady

I think this is a very fundamental optical illusion with a focus on optical, where air temperature bends light so makes you perceive something different from what it actually is.

It's much more related to optics than direct perception. Your brain is drawing the correct image its received, the light has just been bent so that it doesn't form an accurate representation of what you're trying to see.

3 years ago by hrnnnnnn

The Action Lab had a great video about this effect recently.

https://www.youtube.com/watch?v=CrgKUFbwNf0

3 years ago by istjohn

Fascinating. From the video, this same effect can even invert the image so that a ship appears to hover upside down: a ghost ship.

3 years ago by stjohnswarts

ghost ship are supposed to hover upside down? I thought they were just supposed to be ghostly and spooky?

3 years ago by undefined
[deleted]
3 years ago by jcims

I love this guy's channel. He's constantly cranking out new ideas.

3 years ago by centimeter

I'm always really impressed how he can make a video that sounds like clickbait, but usually go into pretty interesting (and accurate) scientific detail.

3 years ago by IgorPartola

This is what I came here for. Thank you for the link.

3 years ago by ridaj

I sort of freaked out the first time I saw something like this.

Then Wikipedia held my hand and said everything was OK and this even has a name:

https://en.wikipedia.org/wiki/Fata_Morgana_(mirage)

3 years ago by midrus

"...The optical phenomenon occurs because rays of light are bent when they pass through air layers of different temperatures in a steep thermal inversion where an atmospheric duct has formed..."

To me that's the most Men In Black explanation I've ever heard.

Definitely confirms this is aliens.

3 years ago by btilly

Here is a lay explanation.

Light travels at different speeds in different substances. But it always takes a path that is locally fastest - meaning that any nearby path would be slower. (This is called the Fermat principle.)

You can see this principle at work when you put a stick into water. Because light travels more slowly in water, the light first heads mostly straight up, then bends when it hits the air. The result is that light does not travel a straight path to your eye. Which means that the part of the stick in the water looks like it is where the light comes out of the water, rather than where the stick is. As a result you can see the stick visibly bend.

Now what is happening here is that you have a layer of warm air over cold air. Light travels faster in warm air. (That is because as air warms it expands, making it less dense. Less dense means that there is less getting in the way of the light and it can move faster.) Therefore that fastest path is for the light to go up into the warm air, go along the warm air, and then dive back down to your eyes.

In many places you can see the reverse of this on hot days where hot ground makes for a hot air layer next to the ground. When the conditions are right the light from the sky can reach your eyes by skimming along the ground, and you get blue patches in the ground. In a desert this can look like water in the distance.

3 years ago by cevn

OK so, that's how the air ripples work for heat... because of the density of the air.

It makes me wonder, if you had a 10 inch globe of vacuum suspended in air, how different looking thru it would appear vs the air. It seems like you might be able to detect it via sight alone.

3 years ago by dbetteridge

Basically the layers of air above the water have slight variations (temperature, humidity, pressure) between them in such a way that they each have a small change in refractive index that over a distance bends light upwards.

Then you have another group of layers of air further up in the 'marine boundary layer' that bends the light back towards the waters surface.

This is called an 'atmospheric duct' and is somewhat similar in the effect to a fibre optic cable.

Poor mans source: I wrote my thesis 5+ years ago on refractive effects in the maritime boundary layer [1]

[1] https://ceed.wa.edu.au/wp-content/uploads/2017/02/DSTO-Refra...

3 years ago by djrogers

Agent D, you're making it worse...

3 years ago by Gupie

Or proof the earth is flat.

3 years ago by saalweachter

Nah, they're just sailing to Valinor.

3 years ago by moron4hire
3 years ago by mordechai9000

There's a spot where I walk my dog near my house. It follows a power line trail up a hill, and you can turn around and see Denali. For whatever reason, on warm spring days Fata Morgana distortion is fairly common from this spot. I've seen it a few times. At it's most obvious, Denali will appear to be sitting on a pedestal of sheer cliffs, thousands of feet high, surrounded by non existent tabletop mountains and improbable, fantastically shaped spires that would be 10,000 feet ASL if they were real. My cellphone camera doesn't do it justice to though.

3 years ago by brundolf

Have you uploaded pictures anywhere?

3 years ago by mordechai9000

No, I just tried posting to imgur and it didn't go so well. It is a white mountain on the horizon, taken with a cell phone. Honestly the pictures don't convey much. If you zoom in, you can see the distortion, though. I'm sure a decent lens could capture it.

3 years ago by x3n0ph3n3

This is not a Fata Morgana, it's a false horizon.

https://www.youtube.com/watch?v=er1mh90wN-k

3 years ago by david422

This new image needs to go in the wikipedia article. The example images are kinda bleh. But this one really illustrates the concept.

3 years ago by Biganon

A fata morgana is a special type of superior mirage, where the object is heavily distorted, often to the point of being unrecognizable. The ship in the article kept its shape and is very much recognizable.

3 years ago by injb

But why does the ship appear in that location, and not the water it's sitting on? What's special about the ship?

3 years ago by pavon

I think the explanation in the article is incorrect. This looks more like a false horizon caused by reflection of the fog on the water, rather than a mirage.

There is fog out past the ship. The water close to the viewer is reflecting the sky, and is blue, while water further out is reflecting the fog. The fog above the horizon blends in with the water reflecting the fog making it hard to see the true horizon line (but it is there in the picture if you look closely). The line where this reflection changes stands out much more strongly and the eye mistakes it for the horizon line.

This page has more examples of cases where these two different effects were confused: https://www.metabunk.org/threads/debunked-fata-morgana-or-mi...

3 years ago by danaliv

I think you're right. I've seen Fata Morgana and it looks nothing like this. With atmospheric ducting you get (even more) surreal images, with all kinds of distortion and mirroring. If you've ever driven through salt flats and seen floating, horizontally symmetric mountains, you'll know what I mean. Look more closely at these pictures and you'll see that the fog and the true horizon are indeed visible.

3 years ago by tobr

As far as I can tell, it’s just a lucky coincidence that the distortion “cropped out” the water in this case, causing an exceptionally clean illusion. Compare with other images of fata Morgana[1] and you can see how it tends to look more distorted.

1: https://duckduckgo.com/?q=fata+morgana&iax=images&ia=images

3 years ago by hu3

From your link I found this picture of 3 flying ships.

https://i0.wp.com/www.astropt.org/blog/wp-content/uploads/20...

I can feel my brain contorting a bit.

3 years ago by hntrader

But again with these 3 ships why is it only the ships themselves being precisely cropped out and not even small remnants of the immediately surrounding water?

3 years ago by voodootrucker

As near as I can tell from the wikipedia link in the comments below, it's because the ship is perpendicular to the water and the light just happens to be being refracted to that particular observer right at the water line.

[0] https://en.wikipedia.org/wiki/Fata_Morgana_(mirage)#/media/F...

3 years ago by x3n0ph3n3

It's not a Fata Morgana or a superior mirage. It's a false horizon: https://www.youtube.com/watch?v=er1mh90wN-k

3 years ago by Someone

The ship is higher up than the water it is floating on.

You don’t see the keel of the ship, but only parts of it that are above the waterline, and not all of those (corollary: this ship is as good as empty)

Less impressive versions of this would show only the top of the bridge, or the entire ship and some of the water it’s floating on (actually, this image might show some water below the ship. That tiny whitish line below it could be that)

3 years ago by leetrout

Some think this affected the crew on the Titanic and prevented them from seeing the iceberg and some closer ships from seeing her.

https://www.popsci.com/science/article/2012-03/today-good-re...

3 years ago by dmix

This picture will help explain the "superior mirage":

https://upload.wikimedia.org/wikipedia/commons/thumb/4/45/Su...

Note in the OP's original link the bottom half is cut off entirely.

https://en.wikipedia.org/wiki/Mirage?oldformat=true#Superior...

3 years ago by x3n0ph3n3

This _is not_ a superior mirage, it's a false horizon.

https://www.youtube.com/watch?v=er1mh90wN-k

3 years ago by dmix

Thanks for clearing that up, I learned something today. That actually makes a lot of sense as well.

It’s interesting the BBC experts didn’t catch the difference but that’s the benefit of the internet I guess.

3 years ago by ryantgtg

Growing up in Santa Barbara, I would see something like this everyday. Freighters going through the channel, the oil derricks, and the Channels Islands all exhibited it.

3 years ago by breck

Oh wow! Thanks for sharing. I thought the original looked super weird, but seeing your "distorted" version instantly brought back flashbacks to when I saw this in South Dennis, MA, a few years ago. I took photos and couldn't figure out what the heck was out there, but it was this. Thanks!

3 years ago by CRConrad

> Note in the OP's original link the bottom half is cut off entirely.

Not by any optical effect, I think -- you're seeing all that's visible of it where it actually is, too: The bit that's "cut off" is just what's hidden below the water line. (Some other post here suggested a thin line of water may actually be barely visible along the lower edge of the ship in the "mirage" photo.)

3 years ago by depaya

Tangentially related, the fantastic WWII submarine book 'Thunder Down Below' talks about a similar mirage issue being a common occurrence in their submarine warfare. They would see ships that appear to be on the horizon but are actually hundreds of miles away.

[0] https://books.google.com/books?id=Jm-iiEis05AC

3 years ago by marshmallow_12

wow! hundreds of miles! that's extraordinary. tell me this is only possible using specialist telescopes etc.

3 years ago by jeffmcmahan

I live on Lake Erie, and I've seen this effect before. There will be a point between the shore and the horizon at which the water takes on exactly the hue and luminance of the sky, and makes lakers, sailboats, buoys, even a nearby lighthouse, appear to hover. If the point of transition in the color of the water is pretty straight and is parallel with the actual horizon, the effect is convincing.

3 years ago by jeffwass

That’s not the case here. In this case the ship was ‘hovering’ due to an atmospheric effect called Superior Mirage.

https://en.m.wikipedia.org/wiki/Mirage#Superior_mirage

3 years ago by treesprite82

The image in the article looks more like a false horizon (change in color of sea makes it blend into the sky), as jeffmcmahan is describing. You can just about make out the real horizon in the image.

Clearer example of false horizon: https://i.imgur.com/WHzQJ3Z.png

A superior mirage would usually cause more distortion and likely wouldn't so cleanly cut out the ship.

Clearer example of superior mirage: https://i.imgur.com/pa16mOk.png

Daily Digest

Get a daily email with the the top stories from Hacker News. No spam, unsubscribe at any time.