You might be a flat-earther if...

I see a lot of flat-earth stuff on Facebook. I don't know how if any of it is sincere, or if most or all of it is just engagement farming or flamebait. I just know I can't look away. The amount of utter ignorance apparently on display astounds me.

It's been well understood for millennia that the earth was spherical. Simple observation proved that: ships leaving port didn't just appear to get smaller as they sailed away; they disappeared from the bottom up as though going over a hill. The shadow cast on the moon during a lunar eclipse was always a circle; only a sphere casts a circular shadow from all angles.

In the third century BC, Eratosthenes measured the circumference of the earth using a couple of sticks and high-school geometry. Some of his assumptions were off (for example, the exact distance and bearing from Alexandria and Syene), but his methodology was sound. Columbus wasn't trying to prove the world was round; that was understood. The dispute was over its size, and whether Asia wa reachable by sailing west from Europe. (Obviously, it wasn't. It was fortunate for Columbus that North America was in the way. He thought the globe was much smaller.) Enlightenment intellectuals in the 18th and 19th centuries concocted the myth that the ancients believed the world to be flat, in order to portray religion as anti-reason. In reality, educated people knew the earth was a sphere. That people today will seriously entertain the notion that we live on a planar surface just goes to show how un-educated we have become.