The measurement of the earth

How big is the earth?
Everyone knows that the earth is round and I would not start a discussion on how important this is for us, our existence and all the living on the earth.
But at the moment we know that the earth is like a ball or better said a squashed mandarin, a new question gets created in our minds: How big is our mother planet, how long is its circumference?


An equatorial circumference of 40.075 km and a polar one of 40.008km.
Today the answer is given quite easily with the help of specific satellites,
the gravity-gradiometry-satellites like GRACE (2004) and GOCE.
Long before Isaac Newton calculated the rotation of the earth and through that its centrifugal force and its real form, long before Columbus started his travel to India in the 15th century, being sure the earth is round, long before the creation of a new measurement method by the mathematician Al-Biruni in the year 1023 and also far before the Arabs found out the earths radius with just a deviation of 2% in the Middle Age, the knowledge about the length of the circumference or specifically the radius of the earth was gained.
So when actually the first person thought of calculating the earth’s size and who later really realized it?
The idea that the earth is round was already created 600 BC by the ionic natural philosophers like Thales of Milet and Anaximander. The evidence for their hypothesis was made afterwards by Aristoteles 400 BC.
It needed nearly 200 years more until Eratosthenes calculated the radius of the earth to be ca. 6.645 km, a length which is wrong just by 4,2%. Fascinating or not?
So what do you believe, do I turn you into ridicule?
If you want to know the answer, look at the solution under my text.

 

Solution:

Everything I told you is the truth and it is also really interesting to find out how Eratosthenes calculated the radius.

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