After getting himself all grumpy about the ways in which statistics are abused, Joshua Hall decided to relax with a little Carl Sagan.
Fun fact: the philosopher Poseidonios of Apameia (c. 135–51 BCE) repeated Eratosthenes’s experiment about a century and a half later. He observed that on the island of Rhodes, the bright star Canopus was just touching the horizon, while at the same time in Alexandria, the star was a few degrees above the horizon. Because the Earth curves between the two places, the star was seen from different vantage points, and thus the angle between Rhodes and Alexandria could be found. Poseidonios was luckier than he knew: both his figure for the distance between Rhodes and Alexandria and his measurement of Canopus’s position were wrong, but the two wrongnesses canceled each other out, giving a reasonable final answer.
(And yes, I employ BCE/CE dating just to irritate people.)