3 ms·

June 19, 240 B.C.: The Earth Is Round, and It's This Big

56 points by nreece 18y ago

jgrahamc 18y ago
There's a clearer explanation of what he did here: http://www.algonet.se/~sirius/eaae/aol/market/collabor/erathost/ http://www.algonet.se/~sirius/eaae/aol/market/collabor/erath... and this is a nice experiment to do yourself.
demallien 18y ago
I'm always left stunned when I read about the achievements of Eratosthenes. I've always wondered why he doesn't get the same recognition as Plato or Aristotle, or even Socrates.
- jgrahamc 18y ago
  " I've always wondered why he doesn't get the same recognition as Plato or Aristotle, or even Socrates." His name is hard to pronounce :-)
- 0x44 18y ago
  I've always wondered why he doesn't get the same recognition as Plato or Aristotle, or even Socrates. Very likely because most of his works were destroyed when the Library at Alexandria was razed, and because he wasn't considered the best at any single subject by his contemporaries.
- bayleo 18y ago
  Either he was not as prolific in the first place, or not as many of his writings have survived to this day. Sadly most of our views of ancient historical figures is plagued by the same myopia. The ticket to lasting fame may not be just success, but may instead be a combination of success and luck in having your works preserved for generations.
- astine 18y ago
  I dunno, I heard about Eratosthenes long before I heard about any of them. Then again, it is probably just the nature of their respective fields. Those three were philosophers, their ideas were applicable to politics and everyday life in their own time and every time since. Physical science is a comparatively narrow field with regard to application. It was only recently that we realized how practical it really was.
- dhotson 18y ago
  I'm a big fan of Archimedes myself. He made some pretty incredible discoveries during his time. http://en.wikipedia.org/wiki/Archimedes http://en.wikipedia.org/wiki/Archimedes
- gambling8nt 18y ago
  He came much later; in particular, he lived shortly after Archimedes, whose existence doubtless steals much of his thunder.
edw519 18y ago
One reason is that Eratosthenes' very own library of Alexandria had been destroyed, and there was no complete backup of its data. Imagine how much different the world would be today if the Egyptians had practiced disaster recovery. (Also a good lesson for a few customers of mine.)
- t0pj 18y ago
  library of Alexandria had been destroyed I think we're still recovering from that infamous day.
  - jsmcgd 18y ago
    I feel sick when I think of all that was lost.
- kyro 18y ago
  Because using Time Machine to recover burnt artifacts would have clearly been the most sensical course of action. Or they should have at least expected a group of people to actually raze such an invaluable cache of human history.
- cconstantine 18y ago
  I've heard it said that if that library hadn't been destroy Columbus may have landed on the moon instead of north america.
lisper 18y ago
There's a flaw in Eratostenes reasoning: you have to assume that the sun is effectively infinitely far away. In Eratosthenes's day there was no way to know this. The one measurement he did does not prove the world is round. It could merely indicate that the sun is nearby. (It makes an interesting exercise to calculate just how near it would have to be, and to design another experiment to eliminate this possibility.)
- brlewis 18y ago
  Was he even trying to prove the world was round? That was a generally accepted assumption.
  - astine 18y ago
    They already knew it was round by watching ships rise up from the horizon. Also, the fact that you can't see Egypt from Crete. If the earth was flat, the sea and earth wouldn't 'pull away' as it went into the distance, it would shrink to a vanishing point and you'd notice the difference.
- gambling8nt 18y ago
  Actually, Aristarchus, a contemporary of Eratosthenes (slightly earlier in fact) determined the ratio distance to the sun/distance to the moon to be about 20 (actual answer is about 390), and that the distance to the moon was about 20 Earth radii (although Archimedes credited him with an approximation closer to 80 Earth radii; the actual value is about 60). This would have validated any assumption about the sun being far enough away to generate essentially parallel rays. Incidentally, the fact that the world was round was probably already known by Eratosthenes' time, since the Greek society was essentially a group of seafarers, and when you watch a ship go out to sea, in addition to appearing smaller as it gets further away, it also appears to sink downwards. They would doubtless have noticed this, and concluded that the Earth was probably round.
  - cconstantine 18y ago
    I've heard the last bit about the boats too. There is a theory that the common folk never really thought that the earth was flat, but a round earth jived with other theories at various times in history (turtles all the way down!) causing the literate few to reject what simple observation makes clear.
arundelo 18y ago
There's a kids' picture book about Eratosthenes called The Librarian who Measured the Earth: http://www.amazon.com/gp/product/0316515264 http://www.amazon.com/gp/product/0316515264

56 points by nreece 18y ago

There's a clearer explanation of what he did here: http://www.algonet.se/~sirius/eaae/aol/market/collabor/erathost/ http://www.algonet.se/~sirius/eaae/aol/market/collabor/erath... and this is a nice experiment to do yourself.

demallien 18y ago

I'm always left stunned when I read about the achievements of Eratosthenes. I've always wondered why he doesn't get the same recognition as Plato or Aristotle, or even Socrates.

jgrahamc 18y ago
" I've always wondered why he doesn't get the same recognition as Plato or Aristotle, or even Socrates." His name is hard to pronounce :-)
0x44 18y ago
I've always wondered why he doesn't get the same recognition as Plato or Aristotle, or even Socrates. Very likely because most of his works were destroyed when the Library at Alexandria was razed, and because he wasn't considered the best at any single subject by his contemporaries.
bayleo 18y ago
Either he was not as prolific in the first place, or not as many of his writings have survived to this day. Sadly most of our views of ancient historical figures is plagued by the same myopia. The ticket to lasting fame may not be just success, but may instead be a combination of success and luck in having your works preserved for generations.
astine 18y ago
I dunno, I heard about Eratosthenes long before I heard about any of them. Then again, it is probably just the nature of their respective fields. Those three were philosophers, their ideas were applicable to politics and everyday life in their own time and every time since. Physical science is a comparatively narrow field with regard to application. It was only recently that we realized how practical it really was.
dhotson 18y ago
I'm a big fan of Archimedes myself. He made some pretty incredible discoveries during his time. http://en.wikipedia.org/wiki/Archimedes http://en.wikipedia.org/wiki/Archimedes
gambling8nt 18y ago
He came much later; in particular, he lived shortly after Archimedes, whose existence doubtless steals much of his thunder.

edw519 18y ago

One reason is that Eratosthenes' very own library of Alexandria had been destroyed, and there was no complete backup of its data. Imagine how much different the world would be today if the Egyptians had practiced disaster recovery. (Also a good lesson for a few customers of mine.)

t0pj 18y ago
library of Alexandria had been destroyed I think we're still recovering from that infamous day.
- jsmcgd 18y ago
  I feel sick when I think of all that was lost.
kyro 18y ago
Because using Time Machine to recover burnt artifacts would have clearly been the most sensical course of action. Or they should have at least expected a group of people to actually raze such an invaluable cache of human history.
cconstantine 18y ago
I've heard it said that if that library hadn't been destroy Columbus may have landed on the moon instead of north america.

lisper 18y ago

There's a flaw in Eratostenes reasoning: you have to assume that the sun is effectively infinitely far away. In Eratosthenes's day there was no way to know this. The one measurement he did does not prove the world is round. It could merely indicate that the sun is nearby. (It makes an interesting exercise to calculate just how near it would have to be, and to design another experiment to eliminate this possibility.)

brlewis 18y ago
Was he even trying to prove the world was round? That was a generally accepted assumption.
- astine 18y ago
  They already knew it was round by watching ships rise up from the horizon. Also, the fact that you can't see Egypt from Crete. If the earth was flat, the sea and earth wouldn't 'pull away' as it went into the distance, it would shrink to a vanishing point and you'd notice the difference.
gambling8nt 18y ago
Actually, Aristarchus, a contemporary of Eratosthenes (slightly earlier in fact) determined the ratio distance to the sun/distance to the moon to be about 20 (actual answer is about 390), and that the distance to the moon was about 20 Earth radii (although Archimedes credited him with an approximation closer to 80 Earth radii; the actual value is about 60). This would have validated any assumption about the sun being far enough away to generate essentially parallel rays. Incidentally, the fact that the world was round was probably already known by Eratosthenes' time, since the Greek society was essentially a group of seafarers, and when you watch a ship go out to sea, in addition to appearing smaller as it gets further away, it also appears to sink downwards. They would doubtless have noticed this, and concluded that the Earth was probably round.
- cconstantine 18y ago
  I've heard the last bit about the boats too. There is a theory that the common folk never really thought that the earth was flat, but a round earth jived with other theories at various times in history (turtles all the way down!) causing the literate few to reject what simple observation makes clear.

arundelo 18y ago

There's a kids' picture book about Eratosthenes called The Librarian who Measured the Earth: http://www.amazon.com/gp/product/0316515264 http://www.amazon.com/gp/product/0316515264