More than 2,000 years ago, Eratosthenes calculated Earth’s circumference without leaving Egypt. As part of a global collaboration, our five schools intend to perform a similar experiment, although we will use some pre-recorded data.
During the vernal and autumnal equinoxes, the sun’s rays shine at a right angle on the earth’s equator at noon. If we measure the shadow of a vertical structure of known length (such as a yardstick), we will be able to use trigonometry or scaled diagrams to determine the angle (𝛉) of the sun’s rays to the structure. Assuming the sun’s rays are parallel, this angle is equal to that of the equator to the location where we made the measurements. Because we know the distance from our location to the center of the earth, we can solve the proportion 𝛉/360 degrees = distance/circumference for the circumference of the earth.
During the vernal and autumnal equinoxes, the sun’s rays shine at a right angle on the earth’s equator at noon. If we measure the shadow of a vertical structure of known length (such as a yardstick), we will be able to use trigonometry or scaled diagrams to determine the angle (𝛉) of the sun’s rays to the structure. Assuming the sun’s rays are parallel, this angle is equal to that of the equator to the location where we made the measurements. Because we know the distance from our location to the center of the earth, we can solve the proportion 𝛉/360 degrees = distance/circumference for the circumference of the earth.
By Francesca Chu