Students to Measure Circumference of the Earth Using Ancient Method


June 20, 2007 – A group of Southeast Missouri State University students enrolled in a physics course this summer will measure the circumference of the earth this week using an ancient method pioneered more than 2,000 years ago by Greek mathematician Eratosthenes.

The students, who are in-service teachers enrolled in PH618 “Topics in Physics Education,” will join a network of about 60 other groups from around the nation and the world in an activity to measure the size of the earth using Eratosthenes’ method from 240 BC. Leading the activity at Southeast will be Dr. Peggy Hill, associate professor of physics.

The activity is planned for June 20-22 to coincide with the same time of year that Eratosthenes did his observation — the summer solstice or June 21. On these days, students will be making measurements of the length of the noon time shadow cast by a vertical stick in order to measure the angle of the sun and, finally, to calculate the size of the earth.

“Science is more about trying to understand ‘how’ we know, rather than ‘what’ we know,” Hill said. “Any time we can do something hands-on it helps us understand how we arrived at an answer.”

Hill said her class is participating in the activity for a several reasons.

First, she said, “physics is a mathematical science and is based on experiment.  Finding the size of the earth involves measurement and the application of mathematics as a tool to aid our understanding.”

Second, she said, the project gets students to look more closely and critically at their world, and to question things they have simply taken for granted.

“This project puts the physics we are using into cultural and historical perspective,” Hill said. “It is amazing to think of how ancient people were able to measure the size of the earth with only sticks, the length of their stride and a knowledge of basic geometry.  Hopefully this is a project the teachers can take back to their classroom to perform at a later date.”

Hill said that if groups collaborate online, as they are this year, the activity provides an opportunity for students to share their data with other groups around the world and to take part in the global community of scientists.

Those interested in learning more about Eratosthenes and his method for measuring the size of the earth may view a video of Carl Sagan explaining his work: (This link directs to YouTube and is outside the Web site of Southeast Missouri State University.)

For more information on the activity at Southeast, contact Dr. Peggy Hill at