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| Authored by: Anonymous on Friday, November 09 2012 @ 09:57 PM EST |
just imagine a triangle, one point being the sun, the sides being the rays of
light that will form shadows later, and the bottom being the ground.[ Reply to This | Parent | # ]
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| Authored by: Anonymous on Saturday, November 10 2012 @ 01:12 AM EST |
Ah, but Eratosthenes had a lucky guess that the sun was
a really long long way away so its rays arrived at earth parallel.
For a lightweight introduction to the errors involved see also
http://en.wikipedia.org/wiki/History_of_geodesy
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| Authored by: Anonymous on Saturday, November 10 2012 @ 08:22 AM EST |
He heard that in (some town) near the first cataract on the Nile, the sun shone
down a well at noon on the solstice.
So he measured the angle in Alexandria, then paid someone to walk to the first
cataract to get the distance.
Another proof is that navigators could get excellent accuracy using spherical
trig and a sextant. If you use plane sailing, errors creep in that spherical
sailing avoids on fairly long voyages.
cheers
Hugh[ Reply to This | Parent | # ]
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