In the mid 20th century
we began launching satellites into space that would help us determine the exact circumference of the earth
which is 40,030 KM
But over two thousand years earlier an ancient Greece man arrived nearly that exact same figure by putting a stick in the ground
Batman was Eratosthenes a Greek mathematician in the head of the Library of Alexandria
Eratosthenes had heard that in Syene a city to the south of Alexandria
No vertical shadows were cast at noon on the summer solstice. The Sun was directly overhead
He wondered if this were also true in Alexandria
So on June 21st, he planted a stick vertically in the ground and waited to see if a shadow would be cast at noon
It turns out there was one of it measured about 7 degrees
Now if the sun's rays are coming in at the same angle at the same time of day and a stick in
Alexandria is casting a shadow
While a stick in Syene is not it must mean that the Earth's surface is curved and Eratosthenes probably already knew that
the idea of a spherical earth was floated by Pythagoras around 500 BC
and Validated by Aristotle a couple centuries later if the earth really was a sphere
Eratosthenes could use his observations to estimate the circumference of the entire planet
since the difference in shadow lengths is 7 degrees between
Alexandria and Syene, that means the two cities are seven degrees apart on earth
360 degrees surface
Eratosthenes hired a man to pace the distance between the two cities and learn there were about 800 KM Apart
he could then use simple proportions to find the Earth's circumference
7.2 degrees is 1/50 of the 360 degrees.
So (800) KM X (50) equals 40,000 KM
And just like that a man
2,200 years ago found the circumference of the entire planet with just a stick and his brain
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