A Tale of Two Bridges and Round Earth

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, formerly West Valley College Astronomy Teacher