|
 

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.


Free 7-Day Trial for TeacherVision®

Sign up for a free trial and get access
to our huge library of teaching materials!

Start Trial

Highlights

Teaching Racism & Discrimination in America
The issues of racism, prejudice, and discrimination have plagued the United States since it was founded, and racially motivated killings still occur with frequency today. Help your students understand the historical contexts of racism—with references on slavery, immigration, and the civil rights movement—to frame your conversation on modern instances of prejudice.

Poptropica Teaching Guides
Poptropica is one of the Internet's most popular sites for kids—and now it's available as an app for the iPad! It's not just a place to play games; each of the islands featured on the site provides a learning opportunity. Check out our teaching guides to four of Poptropica's islands: 24 Carrot Island, Time Tangled Island, Mystery Train Island, and Mythology Island.

Teaching with Comics: Galactic Hot Dogs
Reach reluctant readers and English-language learners with comics! Our original teaching guides to the Galactic Hot Dogs comic series (chapters 1-4 and 5-8), as found on Funbrain.com (and now in print!), will take students on a cosmic adventure while engaging their creative minds. Plus, find even more activities for teaching with comics, featuring many other classic stories.

July Calendar of Events
July is full events that you can incorporate into your standard curriculum. Our Educators' Calendar outlines activities for each event, including: Canada Day (7/1), Independence Day (7/4/1776), World Population Day (7/11), Bastille Day in France (7/14), National Ice Cream Day (7/19), First Moon Landing (7/20/1969), World War I Began (7/28/1914), Author J.K. Rowling's Birthday (7/31/1965). Plus, celebrate Read an Almanac Month and Recreation and Parks Month all July long!

Videos
Interested in using different types of media in your classroom? We have a growing collection of videos, with related activities, for holidays and events, including: Independence Day, slavery & the Civil War, American History, U.S. Presidents, handwashing awareness, the Common Core, women's history, Memorial Day, and the environment. Enjoy!