Entry 1056, on 2009-07-18 at 20:41:19 (Rating 2, Science)
Earlier this year, in blog entry number 934 of 2009-01-26 and titled "Those Greeks!" I talked about how impressed I am with the achievements of the ancient Greeks. Today I heard in a podcast that June 19 was the anniversary of Eratosthenes' discovery of the circumference of the Earth. OK, so I'm a month late but I would still like to say a bit about how brilliant that discovery was.
He found the answer by performing a simple experiment in the year 230 BC. The answer he got was 252,000 stadia but the size of the stadion (or which type of stadion he used) is uncertain so we can only say the measurement he got translates to about 39,000 to 46,000 kilometers. The current measurement is 39,940 kilometers (through the poles, around the equator is quite a bit more) so his result is really totally remarkable, in fact I would be tempted to suggest an element of luck must have been involved!
But it wasn't just the fact that he got such a good measurement that impresses me - it was that he decided to answer the question by finding out. A lot of philosophers had thought about questions like that and come up with answers which seemed right or fitted in with their ideas of how the world worked. But Eratosthenes decided, instead of thinking about it, to just find out.
He measured the distance from Alexandria to Syene using the speed of caravans of camels! To improve accuracy the average of several measurements was probably used. Then he observed the shadow of the Sun when it was overhead in one location (unfortunately his original description is lost but some accounts say he used a deep well, others a stick in the ground). He figured from the difference in the two angles that the difference between the two locations was 7 degrees and it was simple maths to get the circumference (and the diameter) from that.
He was also the director of the Library at Alexandria, created the "sieve of Eratosthenes" which is a mathematical procedure to generate prime numbers, estimated the distance to the Sun, estimated the distance to the Moon, measured the inclination of the ecliptic, created a catalog of hundreds of stars, mapped the route of the Nile, invented the armillary sphere, mapped the entire known world at the time, and discovered the tilt of the Earth's axis (23.5 degrees). In old age he became blind and died of voluntary starvation in 195 BC.
He estimated the distance to Sun at 804 million stadia (120 million kilometers). The real distance is 150 million kilometers so this is also an impressive achievement. Interestingly the fact that the Sun was very distant was a necessary prerequisite for the measurement of the Earth's circumference to be made.
When I read about the brilliance of people like Eratosthenes and Socrates (if you can take stories of Socrates' life literally) and other aspects of their lives such as their extraordinary deaths, I feel a sort of geeky science hero worship which might be similar to the way religious people feel about their heros.
Of course, there is a difference. My heros really existed and most likely did what the records say they did (there are some historical uncertainties of course) unlike the religious stories which are either highly doubtful or definitely untrue.
I know I sound like a real geek saying that someone like Eratosthenes is my hero where most people would say the latest pop star, sport hero, or TV character was theirs, but I don't care. I'm actually proud to be a science and technology geek. My hero is still revered over 2000 years after his death. I wonder how many pop stars will have fame that lasts that long!
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