#base sixty

Longitude doesn’t represent distance—there, I said it

In the last post I said I’d tell you how Eratosthanes knew how many degrees of longitude Benghazi is from Alexandria.

We know that lines or parallels of latitude are about 69 miles apart. Latitude measures degrees of two 90° quarter-circles, each starting at the Equator and ending at the poles. The Equator is 0° and the North & South poles are 90°.

Longitude measures time.Or to be more precise,…

We don’t have Ptolemy’s original map. It’s one of those documents lost to history. Lucky for us there’s a copy made by monks centuries after Ptolemy shuffled off the ol’ mortal coil. I drew this version of Ptolemy’s map showing only the longitude lines. He drew them curved to give you the idea that the world is round.

So Eratosthanes and Ptolemy knew that the Earth was round. And it was…