How an ancient polymath first calculated Earth’s size, as told by Carl Sagan

In this clip from the celebrated science education series Cosmos (1980), the astronomer Carl Sagan explores the life and legacy of the ancient Greek polymath Eratosthenes, who, in the 3rd century BCE, not only understood Earth to be spherical, but was able to calculate its circumference with remarkable accuracy. In detailing Eratosthenes’ ingenious methods, Sagan provides a fascinating science history lesson that doubles as a tribute to the remarkable ingenuity of ancient thinkers, who were able to uncover extraordinary truths with the simplest of tools.

Via The Kid Should See This