The Librarian who Measured the Earth
When did people first realize that the earth might be round rather than flat?
Apparently
Aristotle in the fourth century BC was convinced of the sphericity of the
earth, because he observed the earth's shadow on the moon during a lunar
eclipse. Less scholarly people like sailors also thought the world may
be round because they observed ships as they approach the horizon. Their
sails appear to dip into the ocean. But how round was the earth? No one
had any idea. At least not until a curious and ingenious librarian named
Eratosthenes (275-194 BC) discovered a remarkably simple method for measuring
the circumference of the earth. This is the story of how he did that.