[aprssig] Re: Metric [[furlongs per fortnight]]
steve at dimse.com
Fri Sep 7 13:57:24 CDT 2007
On Sep 7, 2007, at 1:05 PM, Mark Fellhauer wrote:
> You follow a celestial reference point. Um, that would be a star.
In an imprecise sense you are right, in that the sun is a star. The
first known measurement of the earth's diameter was calculated using
the angle of the sun during the summer solstice. In Egypt it was
known to be 90 degrees, because the sun shone on the bottom of deep
well (by coincidence along the Tropic of Cancer) but in Greece
Hipparcos measured a smaller angle, and from that he calculated the
value of the earth's diameter with less than 5% error.
An interesting aside, the Romans "improved" the calculation to an
error of almost 40%, and this erroneous value was believed for a long
time. Despite what you may have heard in grade school, no one, not
even the lowest sailor with Columbus, believed the earth was flat in
1492. However, because they thought the earth was much smaller than
it really was, they expected to hit the orient long before they
landed in the Bahamas. It was this unexpected delay in landfall that
nearly led to the mutiny we were told about. I think the truth is a
far more interesting story, but for some reason people prefer the
earth is flat story...
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