Sunday, October 19, 2008

Did You Know...

Recently I picked a up a book titled The Intellectual Devotional. It is set up to provide the reader with 365 brief bits of knowledge from seven different categories: History, Literature, Visual Arts, Science, Philosophy and Religion.

From the Science category this week was about Eratosthenes. This Greek scientist lived from 276-194 BC and was the chief librarian at Alexandria. He developed a way to measure the circumference of the Earth and came up with a surprisingly close measurement.

Eratosthenes knew of a well near Syene, Egypt that was directly below the sun at noon on June 21st, the longest day of the year. This was known because the sun shone directly down to the bottom of the well. Knowing that if the sun was overhead in Syene it must be hitting the Earth at an angle in Alexandria(due north of Syene, Egypt). At noon of the 21st of June, he measured the angle of the sun's shadow in Alexandria.

Eratosthenes knew that the angle of the shadow of the sun would be equal to the angle formed by the two cities and the center of the Earth. He divided the angle by 360 (degrees in a circle) to determine the fraction of a circle that separated the two cities and came up with one-fiftieth. If one were to travel the distance back and forth between the two cities fifty times it would be the equivalent of traveling around the world. Eratosthenes hired a pacer--a professional walker trained in taking perfectly equal steps--to measure the distance between the cities. Using the information from the pacer, Eratosthenes estimated the circumference of the Earth to be 24,700 miles. Using the same principles today the Earth's circumference (pole to pole) is measured at 24,860 miles (24,902 around the equator).

Amazing! The pacer walked a distance of approximately 494 miles and Eratosthenes came up with a measurement that is off by so little a margin of error (.6 of 1 percent)!


By the way, if you want to hear a great endorsement from a high profile Republican, check out this post at FAA Follies. Do yourself the favor of listening to the long version (8 minutes) at the end of the post.
I know, I know. Pointing you to another political blog isn't much different than posting it myself--but Paul does a much better job than I could do.


Mike said...

Eratosthenes is proof that religious fanatics can take us backwards in time. The dark ages took this idea a squashed it.

And remember Bagadad was once the center of intellectual thought.

Mike said...

The dark ages took this idea AND squashed it. Sheeeze I hate typos.

Kevin said...

Yes, Paul does a great job over at the Follies. The comments section is often times a good read as well.


I will check out Paul's blog. I love this history and am so amazed that this guy could do this so long ago. I don't know why I should be amazed but it just seems that back then it would have been much more difficult but maybe not. I could not figure that out today. Happy to stop by and say hello!

Sherer said...


I am glad to have found your blog. What an interesting post. Mr. Eratosthenes seems like an incredible fellow. Amazing discovery.

Reminds of how they discovered the speed of light by witnessing the moons on Jupiter.

Great stuff.


John said...

Thanks, Jesse. Welcome to Out of My Hat. It's an honor to have you spend a few minutes of your day here. Check out some of my favorite blogs, too. They are a great bunch of writers from many different backgrounds!