A Tale of Two Bridges - Measuring Earth's Radius - Virtual

Can you measure the radius of the Earth from an office window? An unusual photograph through a telescope of two San Francisco bridges clearly shows the curvature of the Earth. Measurements from this photo, bridge dimensions, and a few calculations result in a calculated radius of the Earth surprisingly accurate! The presentation will review three models of the Earth and the line of sight to the bridges, each successively more complex, but with increased accuracy as the payoff. Compared to the approach employed by Eratosthenes in 200 BC, a more complex approach adjusts for the refraction of light and yields results closer to USGS estimates for the Earth’s radius.

Speaker Clinton Lewis is a former Astronomy Teacher at West Valley College in Saratoga, an avid amateur astronomer and member of the Peninsula Astronomical Society. His other interests include modeling various forces on low Earth satellites. Clinton’s former day jobs included running a planetarium, determining space satellite orbits, and modelling DNA base detection in the 96 capillary sequencer used in the human genome project.