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From: R Kym Horsell <kymhorsell@gmail.com>
Newsgroups: alt.astronomy,sci.astro
Subject: Re: I Used To Be a ball-Earth Believer, Now I know Earth is Flat!
Date: Wed, 17 Jul 2024 02:33:44 -0000 (UTC)
Organization: kymhorsell.com
Sender: R Kym Horsell <kym@otaku.sdf.org>
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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.