June 19, 240 B.C.: The Earth Is Round, and It's This Big.And this is a big deal for GIS folks. We teach that Eratosthenes was one of the first scholars to calculate the circumfrance of the earth, a basic measurement needed for mapping of the earth to occur. Now there are literally 100's of ellipsoids/spheriods that approximate the shape and the size of the earths surface. These ellipsoids have evolved over time as technologies have advanced and more accurate measurements of the earths shape and size have been made. What's amazing is how close Eratosthenes was to todays estimates of the circumfrance of the earth.
http://www.wired.com/science/discoveries/news/2008/06/dayintech_0619
Depending on the source, it is thought Erathosthenes was between 10 and 20 % off of the 'actual' circumference of the earth. Although, we still debate about the 'actual' circumfrance.
Some reasons it is so amazing how close his calculation were:
- the well in Syene was not at 23.5 degrees (the Tropic of Capricorn) like he thought.
- his calculation of the distance between the well in Syene and Alexandria was not completely accurate
At any rate... it was neat to see this on http://www.wired.com/ last week. I just got the post up after starting on the solstice last Thursday.
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