Estimate the Circumference of the Earth using Eratosthenes' Method Content Material Student Directions: Open and print student worksheet - Eratosthenes.doc Background Information - A brief introduction and background information about Eratosthenes' study. Part A: Estimate the circumference of the Earth using Eratosthenes' calculations - Learn how Eratosthenes estimated the circumference of the earth and repeat his calculations using his measurements. Part B: What happens if there IS a shadow at both sites? - Learn how to calculate the central angle from the measurements of shadows cast from any two points on earth.   Graphics: Graphic A: The central angle between the two cities equals the difference of the two sun angles. Graphic B: The central angle equals the sum of the two sun angles when the cities are on opposite sides of the sun's zenith. Graphic C: How to use trigonometry to calculate the sun angle. Graphic D: How to calculate the circumference of the earth.   Referenced URLs & Java sketchpad sketches: Java sketchpad sketch: Relationship between one sun angle and the central angle (from Part A). Java sketchpad sketch: Relationship between two sun angles and the central angle (from Part B). Distance Calculator (back-up): Use to enter the geographic location of each of the cities and the longitudinal point on the equator (lat., long.) to determine the distance to the equator.   Help Files: Why Local Noon? - An explanation of what local noon is and why each of the schools measure the sun angle at this time. Why north/south and not just the direct distance? - An explanation of why the north/south distance should be used to determine the distance between two cities.   (NOTE: this RWLO is based on the Noon Day Project)