ERATOSTHENES: The Librarian Who Measured the Earth

The librarian who measured the earth, written by Kathryn Lasky and illustrated by Kevin Hawks, tells the story of the greek mathematician and philosopher Erastothenes and how he came to measure the Earth. Our story begins long ago with the birth of Erastothenes in the city of Cyrene. As a young man, Erastothenes was always curios, following the trails of ants and questioning how stars remained in the sky. When he came of age, Erastothenes entered the gymnasium (the formal name for the academic academy) where he excelled in learning of all types. When he became a young adult, Erastothenes moved to Athens, the center for culture and learning in that day in age. In Athens, Erastothenes became a key society player. In Athens Erosthenes became a prodigious recorder of history, including recording the winners of the olympics, and a noted scholar. Around this time he was asked by the king Ptolemy II asked Erosthenes to tutor his son, Philopator. Upon accepting the position, Erasthothenes moved to Alexandria and became a member of the great library. At the Library of Alexandria multiple great inventions including a water-automated clock and improvements to papyrus writing. Erasothenes continues to tutor Philopator, but questions still plagued his mind. After the passing of the head librarian, Erastothenes was awarded the position of head librarian, giving him all the available resources. Our story ends with Erastothenes computing possibly his greatest equation. One day, Erastothenes heard from a friend that there was a point during the year in Alexandria where the sun cast no shadows. Erastothenes theorized that this event must occur yearly. EThen, Erastothenes had another thought. If we can usual triangles to measure the distance of unknown hypotenuse, then perhaps we could use the hypotenuse as a diameter and measure the circumference. But Erastothenes knew he would need more information on history, geography, and cartography before he could conduct his experiment, but no such one scroll existed. It took Erastothenes many years, but he finally put together the world's first real book on geography, making him the world's first cartographer. But he also knew that he would need real mathematical data to complete his experiment. So, Erastothenes calculated  the shadows cast in his home town of Cyrene, by making the trip by camel and erecting a large sun pole in the city's center on the same date and began to put a triangle measurement together. In Alexandria, he found a well where the sun light the water but not the edges of the well, meaning the sun was directly over head. The measurements helped Erastothenes develop a grand triangle for the Earth. The story ends with Erastothenes almost exactly measuring the circumference of the Earth and  letting the world now.

How did he do it? Through traveling, Erastothenes measures the distance between Cyrene to be roughly 5000 miles. He realized that the Earth is mostly a perfect circle and would therefor has a measurement of roughly 360 degrees. Through calculations he came to realize that this meant that the distance between the two cities was roughly 7 degree of the Earth's diameter. And while the actual calculation involved a little more parralax-esque math, I'll use what the book used.
7            5000
----- = ----------
360           C

 50000
--------  (360) = 7
    C

5000(360)=7(C)

360
----- (5000)= C
7

C= 257,142.857

That is actually pretty darn close!

For reference: 360 is the measure of the Earth
7 degree is the measure of Cyrene to Alexandria
5000 is the distance between the two cities
C is the (then unknown) circumference of the Earth.


b.
I've written a story on this exact event for precal and coming from a physics background, stories and literature always make things easier. In fact, there is very little you learn in physics that doesn't come from a literature or story perspective. There is just something about all those big, mathy concepts that are so much easier to grasp in stories. Erastothenes' story is our introduction to the method of stellar parallax, which would go on to be the bases of my studies into multi-universe expansion. That's one BIG math concept I would NEVER have grasped so easily without a story. I like to think that math is so much easier to get in story form because I am a very tactile learner. Stories will always give me more "concrete" concepts that my brain can wrap around and play with, helping me (and other readers) put information together in their own way.