I'd never seen this before

Tina writes:

Gee, wrong again. I haven't run the numbers, there may be a line of
sight, but the only way a human pilot would see a tower top under
these conditions is at night if it had a bright flashing light on top
of it. Real eyeballs in the daytime would not be able to see it, even
if it was in the line of sight.

An object 1000 feet in size would be visible from about 1100 nm away, under
ideal conditions. A flashing light could be visible from any distance,
depending on its brightness. I _did_ run the numbers.

On 1 Jan, 22:07, Tina wrote:
You can be fairly sure he used someone else's equations for line of
sight. I'd bet a significant sum he could not derive them himself. He
and Euclid would not have gotten along.


Him and counting using popsicle sticks wouldn't get along!

Bertie

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

Mxsmanic wrote:
Tina writes:

Gee, wrong again. I haven't run the numbers, there may be a line of
sight, but the only way a human pilot would see a tower top under
these conditions is at night if it had a bright flashing light on top
of it. Real eyeballs in the daytime would not be able to see it, even
if it was in the line of sight.

An object 1000 feet in size would be visible from about 1100 nm away, under
ideal conditions. A flashing light could be visible from any distance,
depending on its brightness. I _did_ run the numbers.

Yeah, maybe an object 1000 feet in diameter but not a tower 1000 feet
tall and 3 to 6 feet wide dipwad.


--
Jim Pennino

Remove .spam.sux to reply.

Tina wrote:
You can be fairly sure he used someone else's equations for line of
sight. I'd bet a significant sum he could not derive them himself. He
and Euclid would not have gotten along.

True and the equations are easy to find on the internet, but they are
all rough approximations.

There is the geometric horizon which assumes the Earth is a perfectly
round billiard ball and the optical horizon which attempts to account
for the fact that the atmosphere bends light and increases the
distance around 10% depending on state of the atmosphere between the
two points.

Given all the ambiguities in the problem, numbers like 92 instead of
"approximatly 90" just show someone can punch numbers into a calculator
without any understanding of the true nature of the problem.

What a surprise.

--
Jim Pennino

Remove .spam.sux to reply.

MX's calculations remember something that was said in an undergraduate
physics course I took: "Assume a spherical cow. . . "

On Jan 1, 6:05*pm, wrote:
Tina wrote:
You can be fairly sure he used someone else's equations for line of
sight. I'd bet a significant sum he could not derive them himself. He
and Euclid would not have gotten along.

True and the equations are easy to find on the internet, but they are
all rough approximations.

There is the geometric horizon which assumes the Earth is a perfectly
round billiard ball and the optical horizon which attempts to account
for the fact that the atmosphere bends light and increases the
distance around 10% depending on state of the atmosphere between the
two points.

Given all the ambiguities in the problem, numbers like 92 instead of
"approximatly 90" just show someone can punch numbers into a calculator
without any understanding of the true nature of the problem.

What a surprise.

--
Jim Pennino

Remove .spam.sux to reply.

On Tue, 01 Jan 2008 23:15:48 +0100, 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.

But the original post was made by a pilot, who could naturally be assumed to
estimate relative altitudes the way pilots do.

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.

Certainly, because a diagram to scale couldn't illustrate anything. While the
distances involved are exaggerated, the visual effects are the same.

The original poster didn't express fear that he was going to hit this far-off
object; he merely reported a curious observation where an object that was
definitely below his aircraft appeared, when first seen, to extend above his
flight path. You stated that this was *not* due to the curvature of the Earth,
I say it is.

Your towers would be several times higher than the orbit of the
International Space Station, and the aircraft would be in outer space.

The International Space Station *isn't* in outer space? Better tell NASA....

Ron Wanttaja

On Jan 2, 11:19 am, Mxsmanic wrote:
Tina writes:
Gee, wrong again. I haven't run the numbers, there may be a line of
sight, but the only way a human pilot would see a tower top under
these conditions is at night if it had a bright flashing light on top
of it. Real eyeballs in the daytime would not be able to see it, even
if it was in the line of sight.

An object 1000 feet in size would be visible from about 1100 nm away, under
ideal conditions. A flashing light could be visible from any distance,
depending on its brightness. I _did_ run the numbers.

Nonsense. If the observer were at 1000' the top of a 1000' tower would
be visible ~75 miles away. A flashing light would not be visible from
"any distance". Think about it -what if it were on the other side of
the planet!

Cheers MC

Ron Wanttaja writes:

The International Space Station *isn't* in outer space? Better tell NASA....

They already know, since they have to boost it periodically in order to
compensate for drag from the atmosphere.

writes:

Yeah, maybe an object 1000 feet in diameter but not a tower 1000 feet
tall and 3 to 6 feet wide dipwad.

There are few thousand-foot towers that are only a metre wide.