It’s high noon, September 21, and the Autumnal Equinox is nearly here (tomorrow, Sept. 22, 2016, at 10:21 a.m.). Harrisburg Academy 8th grade ancient history students scramble outside to set up their equipment and await the noonday sun, in an attempt to take measurements of the sun’s shadow and calculate the circumference of the earth as ancient geographer and mathematician, Eratosthenes (240 BCE), did more than 2,000 years ago.
Like Eratosthenes, the project lives on in obscurity, except for, perhaps, ambitious physics students — but the class is willing to give it a go! Using two eight-foot rods, levels, measuring tapes, protractors, a stopwatch, and string, the students report to their stations and assignments.
Helping us with our project are two civil engineers: one, located in Charleston, South Carolina, and another in Huntington Valley, Pennsylvania. They, too, are taking measurements of the sun’s shadow at noon in their respective locations to compare with our class’ measurements. Academy alumnus, Greg Stewart ’02, will report his readings from Charleston, and our own 8th grade engineers will compare their results with his. Ultimately, our students’ calculations should provide us with a close approximation of the earth’s circumference.
A second experiment takes John Fenn’s measurement of the shadow his rod casts at noon in Huntington Valley, 95 miles east of the Academy. The idea is for our students to compare the length of their shadow here at noon with John’s shadow in Huntington Valley. A stopwatch marks the passage of the sun overhead until the Academy’s shadow reduces to the exact length of John’s shadow a few minutes before. Marking the time it takes to travel the 95 miles between the sites, our students will be able to calculate the circumference of the earth at the 43rd North Parallel.
Our theme this year is, “To understand this you must know about that.” Eratosthenes’ calculations came within 195 miles of the true size of the earth at 24,902 miles. With data in-hand, it is now time to calculate and analyze our own results. Stay tuned for more on the accuracy of our own experiments and if they replicated Erastothenes’ work.
We study ancient history for so many reasons, only one of which is to recognize the connections between math, science, and history. Eratosthenes also calculated the Tropics of Cancer and Capricorn within a quarter of a degree, plus other contributions to mathematics. He knew more about the size of the earth 17 centuries before Christopher Columbus (Columbus estimated the earth as being only 18,000 miles around, which should explain why he believed he reached the outskirts of India and not two unknown continents that were in his way!). Teaching at the Academy provides educators with the freedom to create engaging and collaborative lessons that respect the connections between educational disciplines. Not only are these hands-on lessons rewarding, they are fun for teachers and students, alike!