Eratosthenes

I am sure that name rings a bell with most of you–well, maybe one or two of you anyway.  He was a Greek geographer from the third century B.C.   He calculated pretty darn accurately the circumference of the earth with the most simple devices and geometric theories.   Theories you studied in your geometry class.

He lived in Alexandria and learned that the noon day sun at certain times cast no shadow in Aswan which was upriver on the Nile.  That would be south for those geographically challenged.  Yet the sun always cast a shadow at Alexandria even at high noon.  You know why it cast a shadow there of course.   Alexandria is farther north in latitude and the sun will always cast a shadow because of the “tilt” of the earth in the more northern latitudes relative to the Sun.   So he designed a simple experiment.  He chose an exact date when the sun would cast no shadow in Aswan and at the same noon time he measured the degree of the shadow cast by it in Alexandria.   The shadow cast was 7 degrees and 14 mins. as we would say in modern jargon. 

He knew the earth was a globe and therefore had 360 degrees in circumference so what did he do?  First he had to calculate the distance from Alexandria to Aswan.  Here was his one “error”.  The tools and devices at hand at that time were not nearly as accurate as ours today.  He had no GPS or even surveyor telescopes or a precise measuring device like a yard stick that could accurately measure the distance.  But he used what was available and estimated the distance from traveler’s tales about  the distance and translated that distance into the then known Greek distances of stadia (about 607 modern English feet) which he estimated to be about 5000 stadia.

What was the next step?   Well, the 7.14 was one fiftieth of a full circumference so he did the multiplication and came out to about 28,000 miles (250,000 stadia).  That was too high by a bit but pretty damned accurate considering his tools at hand and his theory and method were dead on.

Don’t shortchange your ancestors.  On the whole they were pretty clever fellows and had intellectual skills equivalent to ours.  What would a man like that have done with a Mac?

Reach down your hand to help someone up who deserves it.  You won’t just be pulling them up, you’ll be lifting yourself.

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