Describe how Eratosthenes measured the circumference of our planet
Describe how Eratosthenes measured the circumference of our planet
Eratosthenes was born on Greek. About 2000 years ago he calculated the circumference of the Earth with much more accurately by comparing the sun's rays in between two locations.
Eratosthenes was a greek mathematician and head of the library in the Alexandria.
He also heard that in Syene a city of south to the Alexandria there was no vertical shadows in the summer solstice. This place was in the Arctic Circle as shown in the figure. The distance between the Syene and the Alexandria was 925km.
He done two well one in Syene and another in Alexandria. He saw that in 21 June the sun rays is coming to the Earth not creating any shadows and goes to the center of the Earth. But in case of Alexandria the well created from the center of the Earth created a sun angle of 7.2°.
This is because of the spherical shape of the Earth.
So he found the angle that the sun rays are producing in the well present in Alexandria was 7.2°. So the angle created in the center also 7.2°. Because the rays and the lines created transversal crossed parallel lines so these two angle must be the same. As the alternate internal angle when two parallel lines transversed are same.
He then measured the distance between the Alexandria and Syene calculated as 925km.
That distance compared to the circumference of the Earth is propertional to the angular measurements that is 7.2°/360°.
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