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From: Barry Schwarz <schwarzb@delq.com>
Newsgroups: alt.astronomy,sci.astro
Subject: Re: I Used To Be a ball-Earth Believer, Now I know Earth is Flat!
Date: Tue, 16 Jul 2024 18:03:34 -0700
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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.

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