Flat Earthers Are Back—You Know the Earth Is Round, But How do You Best Make the Argument?

BY DANIEL LOXTON

RECENT NEWS STORIES,1 CELEBRITY ENDORSEMENTS, and Google search trends2 have highlighted an apparently growing conspiracy theory belief that the Earth is not a globe, but instead a flat disc. According to believers, government forces promote a completely fictitious model of the cosmos in order to conceal the true nature of the Earth. Are these claims true?

No. The Earth is Round

The evidence for a spherical Earth is overwhelming. 3 Most obviously, there are many thousands of images and videos of the Earth from space, including a continually changing live stream view of the globe from the International Space Station—not to mention all the astronauts who have personally seen the Earth from orbit. Flat Earthers claim that all images of the globe are fraudulent inventions, and all testimony from astronauts is false. It is unreasonable to dismiss all of the evidence from the entire history of space exploration, especially when there is zero evidence for a decades long “globularist” conspiracy. However, we do not need to rely on evidence from modern space agencies to confirm the roundness of the Earth for ourselves.

The globe has been clearly understood for thousands of years. Indeed, this was one of the first cosmic facts to be worked out correctly by ancient people because evidence of a spherical Earth is visible to the naked eye.

By the time of the philosopher Socrates and his student Plato, many Greeks understood that the Earth could only be a sphere. Sailors would have noticed that the sails of approaching ships appeared before the hulls of the ships became visible because the surface of the sea is slightly curved, like the surface of an enormous ball.4When you sail toward a ship, island, or lighthouse, their tallest points are the first thing to peek up over the curve of the horizon.

Plato’s student Aristotle offered further “evidence of the senses” to support his own conclusion that the Earth “must necessarily be spherical.” First, there was the evidence of lunar eclipses. When the Moon passes through the shadow of the Earth, that shadow is always the circular shadow of a sphere. Also, Aristotle argued, “our observations of the stars” make it clear “not only that the Earth is circular, but also that it is a circle of no great size.” He pointed out that “quite a small change of position to south or north” significantly changes “the stars which are overhead, and the stars seen are different, as one moves northward or southward.” Just as ships can be hidden from view by the curvature of the horizon, so too can the stars.5

The debate about the shape of the Earth has been settled for over two thousand years. An ancient scholar named Eratosthenes—the head of the famous library of Alexandria in Egypt—even correctly approximated the circumference of the Earth using experimental measurements of shadows in two cities and some geometry.6 (Figure 1)

Despite modern legends about Medieval backwardness, there never was a time when educated people went back to thinking the Earth was flat. Once discovered, the true shape of the globe was too simple and useful a fact to be forgotten. Sailors were reminded of the planet’s roundness every time they climbed a mast to see further over the horizon or looked to the stars to determine their position. By the time of Columbus, his crew and even his critics understood that our world is a globe.7 It had been an established fact for centuries. For example, here’s a passage from the popular astronomy textbook On the Sphere of the World (Figure 2), published over 250 years before Columbus sailed: