I'd never seen this before

On 1 Jan, 22:15, Mxsmanic wrote:
Ron Wanttaja writes:
No. *Pilots are accustomed to judging the altitude of other aircraft based on
whether it's above or below the horizon. *This is great for collision avoidance,
but doesn't work at longer ranges. *ANYTHING located at the viewer's horizon
will appear above the altitude of the observer, and it *is* due to the curvature
of the Earth. *See:

http://www.wanttaja.com/los.jpg

Normally, though, details at such distances are obscured by haze.

But the original post made no mention of the horizon.

On a flat surface of infinite extent, the horizon is always at eye level, no
matter what your position. *On a flat surface of finite extent, it is always
slightly below eye level, depending on how far away the edge of the surface
is. *On a spherical planet, the horizon is still lower; to find its distance
(assuming smooth terrain), add your altitude to the radius of the planet,
square it, subtract the radius of the planet squared, and take the square root
of the result. *At an altitude of 3000 feet above smooth terrain (such as
water, or a dry lake), the horizon on Earth is 58 nm away. *If you are six
feet tall and standing on the surface with smooth terrain (or if you are in a
rowboat on a calm ocean, for example), the horizon is just 2.6 nm distant.

Your diagram is interesting, but since it dramatically overstates the height
of towers and dramatically understates the size of the planet, it's a bit
misleading. *Your towers would be several times higher than the orbit of the
International Space Station, and the aircraft would be in outer space.

On a flat surface, anything moving down in your field of view is something
you'll fly over, and anything moving up is something you'll hit. *The
curvature of the Earth complicates this, but the curvature is gentle enough
that anything affected by it is too far away to be an immediate hazard,
anyway. *At 3000' AGL, you could see Mount Everest from 239 nm away, but since
a small plane might take two hours reach it, you'd have plenty of time to
evaluate it as a hazard.

Thought experiments like this can be interesting. *People often say that the
Concorde was wonderful because you could see the curvature of the Earth, but
the fact is that you can see the curvature from anywhere, even a hill
overlooking the beach. *It just gets more obvious as you move further away
from the surface. *From an airliner at 39,000 feet, the view extends for well
over 210 miles in every direction. *I was once amused to discover on a flight
from Phoenix to Los Angeles that I could see both cities from my window at the
same time at the midpoint of the flight.


the only curavture you've ever seen is that of your butt as you
inserted your head all those years ago.

Bertie