He Figured Out How Big the Earth Was

Eratosthenes Picture Public Domain. Courtesy of Wikipedia.

On this day in ancient history - June 18:

Perhaps on this day in 240 B.C., Eratosthenes measured the circumference of the Earth. He figured it out using the shadow of the solstice sun at two locations. You may have heard that in the Middle Ages people thought the earth was flat, but such a calculation as that of Eratosthenes relied on a model of the earth that was not flat. Read more about this great, but always "second best" mathematician: Eratosthenes.

Related:

• Solstice at Newgrange
• Standing Stones of Callanish
• Library of Alexandria
• Library of Alexandria Scholars