Re: I Used To Be a ball-Earth Believer, Now I know Earth is Flat!

In alt.astronomy Barry Schwarz <schwarzb@delq.com> wrote:

On Tue, 16 Jul 2024 18:52:37 +1000, Daniel70
<daniel47@nomail.afraid.org> wrote:
 

Didn't The Egyptians conduct a similar experiment even earlier than that
.... by measuring the length of the shadow of a (vertical) pole at
mid-day at two different locations??
>
In a related effort, my Niece and Nephew-in-law took their 6 yo son and
2 yo daughter on Holidays to Maroochydore on Queensland's Sunshine
Coast. Just prior to landing, Oscar said he could see Japan out the
plane's window.

 
From Maroochydore to southern Japan is about 6,800 km so this is
pretty unlikely without a monumental atmospheric inversion.  Even
Papua New Guinea at 2,000 km is too far away.
 

If the Horizon is about 20km away from about two meters high, how far
away is the Horizon when at (What's a normal'ish flight level??) 10,000
meters??

 
At 2 m (.002 km), the horizon is approximately 5 km distant.
 
At 10,000 m (10km), the horizon is approximately 357 km distant.
 
Both figures computed using a spherical Earth with a radius of 6378.14
km.
 
In general, at x km above the surface, the horizon is
sqrt(x*[12756.28+x]) km distant.

The easy memory device is -- to see a point 60 deg of latitude away
from where you are you have to be 1 earth radius above the surface ~= 6400 km.
To see 30 deg away you need to be 15% of R above the surface ~= 1000 km.
Of course if the earth is flat then you can probably see Japan from your back
porch.

--
[Outsider Science:]
[Outsider art] could be by a mental patient, a hillbilly or a chimpanzee.
-- "Astrid Weller", The Simpsons, 1999.