The Librarian Who Measured the Earth

The Librarian Who Measured the Earth
Lorena Aguilera

1. The Librarian Who Measured the Earth is a book written by Kathryn Lasky and illustrated by Kevin Hawkes. The book is a colorfully illustrated biography of the Greek philosopher and scientist Eratosthenes, who compiled the first geography book and accurately measured the globe's circumference. Eratosthenes was born over 2000 years ago, and since a young age, he was curious and full of wonder. Eventually, he moved to Athens to learn more, and in there, he made a chronology of all the important dates in the history of Greece and wrote a book on the constellations. His name began to get around, and by the time he was 30, the ruler of egypt asked him to serve as a tutor for his son in Alexandria. He expanded his knowledge with the books he found there, especially with the ones about geography, which was his main passion. By Eratosthenes' era, people had known for sure for over 100 years that the Earth was a sphere. He started collecting information and figuring out mathematical methods to include the size of the Eath in the first complete geography book. He knew that the Earth was a sphere like a grapefruit, so he thought that if he could figure out the distance along the edge of one section and how many same-size sections it would take to make up the whole sphere, he could then calculate the whole distance around. Eratosthenes knew that every circle is made up of 360 degrees, so if he could measure the inside angle of one section, he could divide 360 by that number and know how many sections of that size would make up the whole. He learned that during the summer solstice, the angle of the sun in Alexandria would shine all the way down to Syene, another city, and that that angle would be the same angle that lay at the center of the Earth. He measured and found out that it was 7.2 degrees, so he divided 360 degrees by 7.2 and got 50: it would take 50 Alexandria-to-Syene sections to make up the circumference of the Earth. He had to determine the distance between the two cities, which was hard at the time because there were no straight roads or paths. He asked the king if people trained to walk with equal steps could be hired to measure the distance to Syene, and the king agreed. It turned out to be 5000 stades (or about 500 miles) from Alexandria to Syene. Eratosthenes then calculated the circumference of the earth. When the earth was measured using all the latest technology recently, there was only a 200-mile difference between the new figure and the one that Eratosthenes had calculated over 2000 years ago.
2. The book is related to the idea of working with units. Although it gives a lot of background on Eratosthenes’ life, I think the main point that is connected to our class is the fact that he only had a few units to work with; back then they didn’t have meters or feet like he have today, much less the technology to do it precisely. He did it by applying a measuring system called stadia, a standard unit of measure during that time period that was based on the length of a typical sports stadium of the time. Eratosthenes was a pioneer in developing mathematical methods and applying them to real life.
3. I think literature is an effective way to teach and learn a mathematical concept because stories attract readers and help them understand concepts more easily, especially if they include pictures or graphics.