KDTWflyer
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Curvature Of Earth

Fri Jul 16, 2004 3:12 pm

At what altitude does the curvature of the earth become readily apparent? FL450 or higher than that? And I don't mean curvature as created by a wide angle lens.
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A/c train
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RE: Curvature Of Earth

Fri Jul 16, 2004 3:31 pm

Go and stand on satellite beach on the atlantic coast near cape canaveral and look out over the ocean, I would say around 6 ft ASL.
 
KDTWflyer
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RE: Curvature Of Earth

Fri Jul 16, 2004 3:36 pm

Yes I know the curvature of the earth is visible when dealing with vast relatively planar surfaces such as the ocean's or very large lakes. I'm asking about at which altitude can one see an appreciably curving horizon and dark blue sky above? I've only been up in the range of FL390 and have not seen curvature but have seen slightly darker sky straight above indicated the increased altitude.
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UTA_flyinghigh
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RE: Curvature Of Earth

Fri Jul 16, 2004 4:25 pm

You can also see it even when ground is not visible :

View Large View Medium
Click here for bigger photo!

Photo © William Ronciere


Taken @ FL390 onboard a 747-4B5  Big thumbs up.

UTA
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RE: Curvature Of Earth

Fri Jul 16, 2004 5:45 pm

a couple of years ago i was flying learjet 31a. cruising altitudes always between fl430 and fl490. max ceiling fl510. above fl 450 you clearly see a little curvature. but more impressive is the pretty dark sky right above you.
yes i can handle that alone. - - -famous last words
 
SlamClick
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RE: Curvature Of Earth

Fri Jul 16, 2004 10:35 pm

This is a subject for some debate.

The true curvature of the earth would be the actual edge of the disk, a great circle of exactly the same diameter as the earth. What you can see from any airplane altitude is a horizon circling you at a few hundred miles away. A small circle.

From 35,000' the horizon is about 230 nautical miles away. So 230nm is the radius of a small circle of the earth's surface that you can see. To see the actual curvature, which is vastly greater than this circle you would have to be able to see the entire earth.

Actual earth-disk circumference is 21,600 nautical miles.
Earth's surface disk visible from FL350 is about 1446 nautical miles.

To claim you can see "the curvature of the earth" from low altitude, like a hundred thousand feet or so, is like putting your eye a couple of thousandths of an inch from a large beachball and believing that you can see its curvature. The math is about the same.

What looks curved is that the horizon is about 230nm away at your twelve o'clock but it is also 230 nm away at your eleven, and your one, and your ten, and your two, and your nine, and your three, and so on. If you can see all the way around (as in, from the basket of a balloon) the effect sort of goes away and you again get the sense that you are just hanging above a big (possibly curved) surface. The line of the horizon curves all the way around you, so hanging above a circle it will look curved.

Again, to see the true curvature, you'd have to be able to see the entire near side of the earth.


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timz
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RE: Curvature Of Earth

Sun Jul 18, 2004 7:29 am

"Again, to see the true curvature, you'd have to be able to see the entire near side of the earth."

Which you can only do from infinite distance, so...

How about this: how high must you be to make it obvious to the naked eye that the Earth isn't flat? If you were a quarter-radius above the surface, the horizon would be 37 degrees below a horizontal plane (i.e. a plane perpendicular to the vertical). An earth that only subtends 106.3 degrees at the viewer's eye is clearly unflat.

But what the original questioner was asking was: at what altitude does the horizon look curved. That's not so easy to answer.
 
darkblue
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RE: Curvature Of Earth

Mon Jul 19, 2004 11:04 pm

I'm not sure that you can see the curvature of the earth from any distance. Even if you were at some extreme distance in space, I don't believe you would have the depth perception to see that the edges are further away than the center. To the eye, the Earth would only appear as a flat disk. Take the moon for example, during a full moon your eyes cannot distinguish from a spherical object and a flat disk. The only thing that shows that it is a sphere is the shadow of the moon upon itself during other phases.
 
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RE: Curvature Of Earth

Sat Jul 24, 2004 12:42 am

The highest altitude I've ever been is 41000ft, at that point you still don't see the curvature of the earth but the sky above you starts getting dark. You would have to go above 50000ft to start seeing the curvature. These pictures, taken from Concorde, show:

taken in flight at 58000ft

View Large View Medium
Click here for bigger photo!

Photo © Sam Chui


taken in flight at 50000ft

View Large View Medium
Click here for bigger photo!

Photo © Bernard Charles



Now that Concorde is gone, you will never see this again. The highest altitude you will ever reach on any airliner is 43000ft.

Above 80000ft you are in space. Only astronauts and military pilots experience that.

Ben Soriano
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Ben Soriano
 
lapa_saab340
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RE: Curvature Of Earth

Sat Jul 24, 2004 1:48 am

You have to be careful when looking at pictures, using a wide angle lens will distort it an exaggerate the 'curvature', making it much more pronounced than your naked eye would see.

Also, 80,000ft is nowhere near space, the SR-71 Blackbird reportedly flew higher than this. Although there is no clearly defined boundary, 100,000m seems to be generally accepted as the edge of space (roughly 325,000ft or so). I think the X-15 still holds the altitude record for an airplane, 107,000m or so. Don't think SpaceShip One went that high.

Cheers
 
darkblue
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RE: Curvature Of Earth

Sat Jul 24, 2004 2:08 am

You have to be careful when looking at pictures, using a wide angle lens will distort it an exaggerate the 'curvature', making it much more pronounced than your naked eye would see.

Yes, and the pictures shown in the earlier posts are a great examples of curvature due to lens distortion. The horizon appears to curve downward towards the edges of the picture. If you looking at the horizon with your naked eye, it would appear flat. If you really saw that downward curvature with your eye, then if you rotate around to look at the entire horizon, you would have a M.C. Escher type of optical paradox.

DB
 
ba97
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RE: Curvature Of Earth

Sat Jul 24, 2004 10:34 am

Looking out windows of planes, the only time I saw the horizon not "flat" but having a distinctive "curve" was on Concorde at 56,000ft. Optical illusion, too many fine drinks...I know it was not straight.

That said, it was way more impressive to see the deep deep blue to black sky and the clouds below passing like we were in a Dash 8 at 15,000ft.
there is economy class, business class, first class...then Concorde..pure class
 
Arcano
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RE: Curvature Of Earth

Sat Jul 24, 2004 1:02 pm

Excuse me, but when you stand in a beach and look to the horizon, don't you realize it's absolutely curve?

Altitude for that: 0

Is it only me????

BTW: If you are thinking maybe Columbus was wrong, you can also note the curve of the Earth during a moon eclipse: the shadow shape belongs to a sphere!
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KDTWflyer
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RE: Curvature Of Earth

Sat Jul 24, 2004 3:38 pm

Now this is high here ...

http://www.spaceadventures.com/media/photo/steps/mig-25/info/382

I would love to do alot of the things at this website

http://www.spaceadventures.com/ but it's all too damn expensive.
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GDB
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RE: Curvature Of Earth

Sun Jul 25, 2004 8:00 am

On Concorde, you needed clear conditions, and really be above 55,000 feet.
So best seen on a BGI sector, usually clear when you reached top of descent at 60,000ft, as the longer BGI sectors usually reached this altitude, as opposed to 58,000ft maximum on a JFK sector.
Certainly, of my 7 flights, the best view was on mine and G-BOAE's final flight, last November to BGI.
To get the best discernible view you needed to look through 2 to 3 windows, positioning your head a few inches from the nearest window and looking through the immediate ones ahead of you as well.
Easier done on a nearly empty air test as I did on OAE last August, positioning yourself you are not in anyone's way or infringing on their personal space is do able if there are only about a dozen people in the whole cabin.
Even given the differing interpretations of what the curve of the Earth really is, if it can be seen on the ground or only in orbit or sub orbit, the sight from Concorde was sufficiently different compared to a normal view from an airliner, given good conditions you could make out a curving horizon in a way not possible from lower levels.
I saw it clearly on five flights, not as definable on one, difficult to make out on one.

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