HoS Advent Calendar 2016

Eratosthenes Measures the Earth

In this 13th/14th-century copy of Cleomedes’ textbook on astronomy, typically referred to as “De motu circulari corporum caelestium,” is this illustration of Eratosthenes’ method for calculating the circumference of the earth. The outer oval is the signs of the zodiac in their zoomorphic/anthropomorphic forms, each labeled with its name. The sun is located in Cancer, […]


Eratosthenes and Second Graders

One recent sunny afternoon, I took a bunch of exercise balls with little sticks taped to them to the local grammar school where I met a class of second graders. As part of my war on the flat earth myth, I had encouraged their teacher to read Kathryn Lasky’s The Librarian Who Measured the Earth […]