Time: Approximately 60 minutes

Materials: Protractor (back-up), ruler, pencil, paper

Implementation: This RWLO can be used either in the classroom to demonstrate the learning objectives or provided as an activity / homework assignment enabling the students to discover the process themselves. Students can work individually or in small groups but it is recommended that each student answer the questions.

Steps:

Read and/or distribute Eratosthenes and Background Information.   Review and/or distribute Part A: Estimate the circumference of the Earth using Eratosthenes' calculations. Students should answer the questions located at the bottom of the page and write their calculations in the space provided or in their notebook. NOTE: there is a fantastic Java sketchpad sketch linked in the page that demonstrates the relationship between the sun angle and central angle when one location casts no shadow (i.e. the sun is directly overhead). It is highly recommended that you use this to illustrate the main point of the activity.   Review and/or distribute Part B: What happens if there IS a shadow at both sites? Students should answer the questions located at the bottom of the page and write their calculations. There are several excellent graphics (A, B, C, & D) linked in Part B and another Java sketchpad sketch that visually demonstrates the relationship between the sun angle and the central angle when both locations cast a shadow. Use the Distance Calculator (back-up) to calculate the distance from each location to the equator.