The Earth is a Globe

 Since the "flat earth" delusion seems to be making a comeback on social media, it's time to reiterate:  people in the Middle Ages knew the earth was a globe.

Okay, most of the population probably never thought much at all about the shape of the planet. But the learned certainly thought about it and knew it was a globe.  It was in fact obvious.  During a lunar eclipse, the shadow of the earth falls on the moon, and it is certainly round.

It couldn't just be a flat circle, because the earth's curvature is clear on both land and sea.  If you watch a ship sail out of harbor into the open ocean, it goes "hull down," disappearing from the bottom up as the ship goes over the earth's curve.  On land, as you travel toward distant mountains they appear to grow, at first you just see the top peaks, then more and more as you get closer, as less is hidden by the earth's curve.

The earth in medieval thinking also had to be a sphere because the heavens were a sphere.  Look at the sky on a clear day. It's a sphere (actually a hemisphere), and we're standing looking up at the inside of a globe.

Ancient people had also known the earth was a globe.  Aristotle in fact set out to calculate the size of the earth.  He underestimated, but it was a good effort.  Unfortunately for Columbus, he not only used Aristotle's estimate, but figured that because he would be sailing west well north of the equator, the distance around the earth was smaller yet, plus he seems to have forgotten to carry the 2... (or the equivalent).  But he and the Spanish court certainly  knew the earth was a globe, just thought the distance from Spain to the East Indies was thousands of miles shorter than it actually is.

(The idea that the Spanish court expected Columbus to fall off the edge of the earth is a complete canard, dating not from 1492 but from the nineteenth century and a "hilarious" anti-Spanish fictional story, written by Washington Irving, better known to us for the Headless Horseman of Sleepy Hollow.)

Where medieval people had their astrophysics messed up was the shape of the solar system.  Rather than seeing the earth and the rest of the planets rotating around the sun, they had the sun and all the planets (all of them globes) rotate around the earth.  Explaining their orbits was really tricky, as they seemed to go backwards sometimes as well as forward.  But they tried.

In addition, they generally assumed that as one went further south one would get progressively hotter, so that as the North Pole was cold, the South Pole was assumed to be hot.  There was also concern about how the people who were thought to live in the southern hemisphere could stay attached to the planet, given that they were (from the point of view of the northern hemisphere) upside down.

Sometimes these southerners were depicted with giant feet and toes, to grip the earth so they wouldn't fly off.  They were also bent 180 degrees at the waist, so that their head was still "up."  Yet other medieval thinkers had it right, that "down" was not an absolute direction but rather toward the center of the planet, wherever one was on it.  Dante, in describing a descent into Hell, said that once you got into the center, where Satan sat frozen in ice, you had to turn around, head where your feet had been, to continue up to the other side of the planet.

 Flat earth folks today have major problems explaining things like, if there's an edge to this flat earth, why has no one ever seen it?  How can planes fly around the world just as if it's a globe, if they argue everything is actually laid flat in two dimensional space?  If you go west from California, how do you suddenly end up on the east side of the planet, next to Japan?

One of the sillier arguments I've seen recently is that we must be a flat, unmoving space, with sun and moon and everything else rotating around us, because if we were actually on a swiftly rotating planet we'd fly off into space.  (Try this analogy: how can we drive along at 60 mpg in a car without being thrown from the front seat into the back seat and out the back hatch by the speed?)

© C. Dale Brittain 2025

For more on medieval understanding of the world, see my ebook, Positively Medieval:  Life and Society in the Middle Ages. Also available in paperback.