I took this photo on a 747-400 while flying over Siberia from Tokyo-London. 747’s top out around 11,000 meters high which = 36,000 feet… It seems to show a clear curvature and I’m intrigued as I’ve never seen that before anywhere near so clearly while flying on many 747 flights at approximately the same height.
Most webpages I’ve found claim that curvature of earth is only clearly visible from 60,000 feet or higher… This image seems to show a clear curvature and I don’t believe it’s from the lens (details below). Was this just an exceptionally clear view where the curvature is visible or is something else causing the apparent curve?
It’s taken with a Canon EOS 7D with a Tamron 17-55mm lens, and I was set to quite near 17mm with this shot. This lens has very little distortion or curvature on other shots, that shouldn’t be the cause…
that makes no sense at all… the horizon is the same distance in each direction so there is no perspective effect that would cause a visible curve in the horizon if the earth was flat.
If the horizon for some reason was closer in the middle you’d see a curve, clearly that’s not the case in this photo.
Off the cuff, it looks like barrel distortion to me and, sure enough, reading up on reviews of the 17-55mm Tamaron, the “cons” of the lens are barrel distortion at the very wide range.
This level of distortion is not clearly visible on normal shots of buildings and other objects with straight lines when set to 17mm… I’ll shoot a grid with it to test and post that as well.
Your flight passed over a distortion in the space-time continuum that resulted in the earth’s curvature being visible from a much lower altitude than is normally possible. Perhaps there was a black hole nearby?
Your lens exhibits a common optical flaw at one of the extremes of its zoom range.
Your camera is not solely to blame - the cabin windows on 747s are not exactly precision optical devices themselves. Last time I looked, the windows consisted of at least three layers of curved glass and plastic.
The curvature of the earth is technically perceptible at 35,000 feet, but it is nowhere near as dramatic as your photo illustrates, and requires a much larger field of view to be perceived at that altitude (and a much more clearly-defined horizon). For all practical purposes, you need to be at an altitude of at least 50,000 feet.
My highly untrained eye detects a difference in the angle of the of the two jet engine openings in the picture. I would think those engines are aligned, and the difference is a result of the lens or window apparent even at the short distance of something less than the wingspan.
In addition we have no idea what the pitch or roll angle of the plane was when that picture was taken. The altitude is also questionable, unless the OP had access to the cockpit instruments at the time.
I don’t know much about optics, but I don’t think the distortion would normally be revealed by taking photos of buildings that are much closer to the lens than the horizon would be here.
I don’t think B747 engines are aligned perfectly (at least they’ve never looked it to me, I assumed it was to compensate for variations in airflow along the span of the wing.) Altitude is normally given on the flight tracking channel of the TV screens.
Edit: The engines won’t look aligned from close range due to perspective. You will see the more of the intake on the outboard engine even if they’re perfectly aligned.
You can check the amount of distortion of your lens by looking at the reviews here. I assume that you meant a Tamron 17-50 ? There are two of them (which I enthusiastically recommend, btw). Both have a rather significant distortion at 17 mm.
Well, as noted my eye is untrained. My first views of the picture left me with the impression that the camera was aligned at right angles to the inboard engine, but after looking at that picture more than I care to, I don’t think that assumption was correct. And the other factors you mention make my own perspective meaningless in regard to the engines. I think the angle of the camera relative to the earth is still in question, not to mention distortion by the window and the lens.
I’d never noticed any great difference in alignment between wing mounted engines, and this photograph apparently doesn’t actually reveal any. But if there were a difference in alignment of the engine from the centerline line of the aircraft, how would that affect stability, initially in the yaw axis? It would seem that the thrust from the engines would have to be directed toward the fuselage in order to avoid having the thrust magnify any rotation on the yaw axis. I guess this is a hijack, but you seem to have shown knowledge of aerodynamics in other threads, so I’ll take the opportunity to ask.
I’ve spent a lot of time looking out optically flat windshields at altitude. Even at 41,000 feet, the 747-400’s service ceiling, there is no visible curvature to the horizon. Not even the “well, if I squint & use some imagination I can almost …” kind. Up at 50,000 feet (i.e. >20% higher) you get into that “well if I squint…” area.
Passenger windows aren’t optically pure. But the outer face is pretty close to dead flat fore-aft and has only a smidgen of curvature up-down. I’m not 100% sure the two panes’ inner and outer surfaces are dead parallel, but there’d not be much reason (and a bunch of extra cost) to make them otherwise. The inner panel is a flimsy replaceable scratch shield and isn’t going to add much aberration.
It’s your camera.
I was actually going to point this out as well, but got distracted looking up the barrel distortion on the Tamron lens. Hell, my $1400 Canon 24-70mm f/2.8L shows perceptible barrel distortion at 24-28mm. Anyhow, I certainly think the glass can be a contributing factor, although LSLGuy’s experience seems to indicate that there isn’t much distortion. I"ll have to pay attention more next time.
Left/right (ie yaw axis), the engines are aligned parallel with the fuselage. Up/down (pitch) is a different matter.
As the wings flex up & down the do a very limited amount of twisting. Controlling that twisting is one of the limiting factors in wing design. But as a result of the varying twist, the pitch attitude of wing-mounted engines is not a constant vs. the fuselage centerline.
I guess I’ll be the dissenter here. It shows the curvature of the earth. I’ve noticed that when you get up over about 5000’ AGL in a private plane, the curvature is very noticeable. I’ve only piloted myself up to just over 14,000’ since it starts getting tougher to breath, but the curvature is very noticeable.
I’m not sure how you don’t see it,** LSLGuy**. Perhaps you’re just too accustomed to it to notice?
Ever look at pics from the top of Everest? There’s alot if you google them. Here’s one of the first I saw:
Every time we do one of these threads on “curvature of the earth”, I’m completely baffled. What are people talking about? There’s curvature of the horizon, which I can see by looking out my office window from an elevation of about 100 feet. You would see this even on an infinite flat earth. Then there’s the fact that the earth fills up less than 50% of one’s field of vision, which effect increases with elevation, and which would not be the case with an infinite flat earth. How anyone can determine what percentage of one’s field of vision is filled up by the earth in the OP photograph, I’m at a loss to say.
I cannot speak to your experience in a plane. However, the photo you linked does not prove the point. Wide-angle and super-wides will show curvature. See the photo of flowers here about 1/3 down the page. This field looks curved but at this scale it is obviously an artifact of the lens. Only lines passing through the center of the image will look straight. Fisheye lenses are an extreme example of this effect. In the photo linked in the preivous sentence, the curvature of the Earth looks negative! That’s because the horizon is below the center line of the image. Note that the curvature appearing both in the OP’s linked photo and in brewha’s linked photo are above the center line.
I am completely baffled by this post. Curvature of the horizon is due to the fact that the Earth is round. At an elevation of 100 feet you can’t see far enough to the left and right to see the horizon curving down in those directions. And the amount of field of vision occupied by the Earth sort of depends on where you’re looking, doesn’t it?
No, absolutely not. Curvature of the horizon is caused by the fact that the locus of points equidistant from an observer is a circle. Imagine yourself standing on a boat in an infinite flat ocean. What would the horizon look like? Would it be square? Triangular? No, it would be round–you see the same distance in every direction (out to where the distant land merges into an indistinct blur), and perceive the shape as a circular curve.
If a round horizon were evidence of a spherical earth, people would have figured out the sphericity of the earth long before 400 BC.
I’m referring to the potential field of vision available to an observer, looking in all directions. An infinite flat earth, with no local obstructions, fills 50% of that field of vision–the lower half. The sky fills the upper half.
On our actual spherical earth, from a low elevation, the earth fills microscopically less than 50% of that potential field. As you gain elevation it fills less and less, until from distant space it becomes a dot like another planet viewed from earth.
