ADVERTISEMENT |  REMOVE ADS

Eratosthenes

Explore connections in mathematics and history with this article on Eratosthenes.
Grades:
9 |
10 |
11 |
CREATE NEW FOLDER
Cancel

Eratosthenes

Eratosthenes of Cyrene was a Greek mathematician who lived from about 275-195 B.C. Today he is best known for his contributions to geography, mathematics, and astronomy. Educated in Athens, Greece, and in Alexandria, Egypt, Eratosthenes was appointed director of the great Library at Alexandria in 236 B.C., where he served for several years.

One famous contribution that bears his name, the "Sieve of Eratosthenes," is a system for finding prime numbers. However, Eratosthenes' most famous accomplishment is his calculation of the circumference of the Earth to a remarkable degree of accuracy for his time.

In determining the circumference of the Earth, he had read that a certain deep well near Syene, a city due south of Alexandria, was fully illuminated by the sun at noon on the summer solstice. The sun, therefore, must have been directly over the well. Seeing that a pole in neighboring Alexandria cast a shadow at the same time, Eratosthenes measured the angle of that shadow and used it to calculate the curve of the Earth. He assumed two things in his calculations: that the Earth is round and that the Sun is far enough away that its rays are essentially parallel. He then used a primitive version of the arc length formula to calculate X, the circumference of the Earth, in the proportion: X/x = Y/y

In this formula, x equals the distance between Syene and Alexandria; Y equals the 360 degree angle of the round Earth; and y equals the angle of the shadow cast at Alexandria.

Eratosthenes also successfully measured the tilt of the Earth's axis, created a catalogue of 675 stars, and wrote mathematical and geographical treatises, all of which are now lost to us. One was titled Platonicus, which dealt with the mathematics behind Plato's philosophy. We do know that he also devised a map of the known world, divided by a system of longitude and latitude.

Your Free Gift

The Ultimate Back-to-School Guide

Teachers are always thinking about their students, but devotion to their progress shouldn’t come at the expense of your own. That’s why we’ve created an “Ultimate Back-to-School Guide” for teachers based on our nine future-ready skill domains.

What you can expect from this guide:

  • Learn 9 ways to become a better teacher by developing a positive mindset.
  • Links to dozens of free resources curated by our experts to help you both in and outside the classroom.
  • Clear steps to improve your teaching and general well-being.

Sign up for a premium membership to get your Ultimate Back-to-School Guide absolutely free!

SIGN UP TO CLAIM YOUR FREE GIFT

ultimate back-to-school guide for teachers

Register