Students observe sun, measure Earth’s radius

By Kurt Hyde
Staff Writer

Students measured shadows beneath the sunshine between X and Y buildings. They stood with rulers, pencils and paper, ready to record the information on March 21, the day of the vernal equinox.

Physics 1403 students used measurements from their shadows to calculate the radius of the Earth.

Chaz Hafey, astronomy and physics lab coordinator, led the students as they used calculation methods similar to those used around 240 B.C. by Eratosthenes, the ancient Greek mathematician, geographer and astronomer. Hafey said the project was selected on the day of the equinox because the math is easier when the sun is directly over the equator.

Anahita Sidhwa, astronomy professor, said Eratosthenes is said to have used the shadow of a stick, but he personalized this exercise by having students work in pairs, and each member measured the other person’s height and the length of their shadow.

Each student calculated the circumference of the Earth using measurements pertaining to his or her own body.

“It looks like everyone’s [calculation] was about 20 percent low,” Sidhwa said.

Hafey said he was pleased with the accuracy considering the equipment used and because the lab was scheduled before the solar noon that day.

If the lab was scheduled an hour later, Hafey said, the calculations would have been closer to the known radius of the Earth.

Student Addie Rule said she had fun measuring her shadow. “I really do enjoy this class,” she said.