Calculating the radius of the Earth

This page authored by Basil Tikoff. The activity was developed by Paul Riley and Basil Tikoff
University of Wisconsin - Madison, Geoscience
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This activity was selected for the On the Cutting Edge Reviewed Teaching Collection

This activity has received positive reviews in a peer review process involving five review categories. The five categories included in the process are

  • Scientific Accuracy
  • Alignment of Learning Goals, Activities, and Assessments
  • Pedagogic Effectiveness
  • Robustness (usability and dependability of all components)
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This page first made public: May 11, 2012


Science students often have difficulty thinking about large spatial scales. The purpose of the exercise is to redo Eratosthenes' calculation of the radius of the Earth using data from to sites in ancient Egypt. The excercise teaches about the methodology of science - how Eratothenes figured it out - rather than worried about what the "right" answer is. It can also be used to discuss the role of models in geological thinking.

Learning Goals

Methods of Geoscience

This activity concentrates on spatial thinking, the role of models, and separating observation from interpretation.

Context for Use

This class was developed for an introductory non-science major class at the University of Wicsonsin. It helps to have it during fall semester so that you can take advantage of the Equinox (~Sept 20). The students need to have mastered:
  1. Fractions; and
  2. Scaling
before they embark on the exercise.

Description and Teaching Materials

It is not necessary, but it helps to have meter sticks and a way of making them stick upright outside.

Teaching Notes and Tips


References and Resources