In a recent Letter to the Editor,1 Hewitt asks whether measurements of the shadow angles cast by a pair of (radially) vertical sticks (which for accuracy could be tall flagpoles) that are a known distance s apart on a spherical astronomical body (which I will take to be Earth) can be used to find the circumference (or simply the radius R) of the planet if the sticks are not on a common line of longitude along with the Sun? The answer is yes, but only if both the horizontal and vertical shadow angles are measured, and not just the vertical angle (call it α) as in Hewitt’s original “Figuring Physics” column.

Assume that a team of students have assembled at each flagpole. They have agreed to make simultaneous measurements at their locations on a sunny day (when the Sun is not directly overhead, so that the flagpoles...

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