Earth Is Round!
The Greek mathematician Pythagoras hypothesized that Earth is a sphere, rather than a disk, in the sixth century B.C. Three centuries later, his compatriot, the astronomer and mathematician Eratosthenes, calculated our planet’s circumference using only sticks, shadows, pencil and paper. Photographs of Earth from space make the case watertight. Yet, flying in the face of NASA snapshots and millions of circumnavigations of the globe, defiant flat-earthers still claim devotion to the horizontal plane.
Every high school geometry student is acquainted with the Pythagorean theorem for calculating the sides of a right triangle, but the equation’s namesake was actually more of a circle guy. Pythagoras, a sixth-century B.C. Greek mathematician, believed that geometric and cosmic perfection were manifested in the circle. His spherical-earth theory, the earliest known, was based purely on his aesthetic desire for a harmonious universe—no astronomy was involved. (Seventeenth-century German astronomer Johannes Kepler, who shared Pythagoras’s belief in the circle’s divine perfection, supposedly lost faith in the harmony of nature after determining that the planets’ orbits were elliptical rather than circular.)
In the fourth century B.C., the Greek philosopher Aristotle looked to the skies to deduce Earth’s spherical shape. He noted the curvature in the shadow our planet casts on the moon during a lunar eclipse and observed that the night sky’s features changed with latitude: “There are stars seen in Egypt which are not seen in the northerly regions.” But the most important figure in early round-earth theory was Eratosthenes. Using observations of varying shadow lengths in different regions on the summer solstice, the third-century B.C. Greek astronomer and mathematician made a near-accurate calculation of Earth’s circumference.
For the land-bound, the vastness of space and the depths of the sea both represent the mysterious unknown, the untouchable, the unfathomable. In Moby-Dick, Herman Melville writes of an ancient belief that “far beyond all visible horizons” the seas “interflow with the blue heavens,” forming the foamy edges of the Milky Way. Carl Sagan, in Cosmos, states that earthlings gazing into the light-dotted blanket of space stand on “the shores of the cosmic ocean.” And many have speculated about whether there are more stars in the universe or grains of sand on Earth.
Several mysteries of the cosmic ocean, including our planet’s shape, have been solved upon our earthly seas. Observers watching a departing ship as it nears the horizon can see it dip by barely perceptible degrees below Earth’s curve until only its mast remains. Mariners likewise notice that the celestial map changes as they steer their ships from one ocean to another. But the distinction between looking out to sea and into space is astronomical in its dimensions: Someone standing on the shore can see about 2.5 miles to the horizon, while on a clear night the naked eye can glimpse the Andromeda Galaxy, 2.5 million light-years away.
The first visual observations of Earth’s roundness were made not by intergalactic spacefarers but by mariners of traditional wooden hull-and-mast ships. Seafarers have an unobstructed view of the horizon, and those who sail the open oceans can detect the planet’s curvature: Just as a ship far out to sea appears to slowly drop below the horizon, when a ship approaches land, the first objects sailors spot are the tops of trees or mountains.
European nations staked out their waterways in the 15th and 16th centuries, forcing mariners to explore new trade routes to the silks and spices of Asia. In 1492 Italian explorer Christopher Columbus found a westward route to Asia that was speedier than the known eastward routes, taking him only five weeks. A small wrinkle: Having landed in America, he was short by the length of a continent and 10,000 miles of Pacific Ocean. The expedition of Portuguese explorer Ferdinand Magellan went the distance, traversing the Atlantic and Pacific Oceans to reach the Spice Islands (Indonesia’s Maluku Islands) and returning home via the Indian Ocean and back up through the Atlantic. This first circumnavigation demonstrated what mariners had suspected for centuries: Earth is round.
Before humans mapped their world, they had mapped the stars. Ancient mariners were trained in celestial navigation, for the map of the heavens was more reliable than incomplete earthly maps. Nautical explorers bound for uncharted horizons understood that you can’t know Earth until you first know the skies.
Ferdinand Magellan was trained in astronomy and cartography, and he made important contributions in both fields. His expedition’s circumnavigation of the globe between 1519 and 1522, completed after Magellan was killed halfway through the voyage in the Philippines, during a battle with a local leader resistant to Christianity, helped fill in the holes on maps both earthly and celestial. After traversing the tip of South America through a channel, now called the Strait of Magellan, that delivered his ships from the Atlantic, Magellan named the still waters approaching Asia the Pacific Ocean. The explorer’s documentation of a faint aggregation of stars visible from the Southern Hemisphere led to its official discovery as a galaxy—the third closest to our Milky Way—and its eventual christening as the Large Magellanic Cloud. In 1989 NASA launched the Magellan spacecraft, sending it to explore and map Venus, as its namesake had done on Earth.
A prominent myth about Christopher Columbus—besides the idea that he discovered America—is that his 1492 voyage proved to a narrow-minded Europe that Earth was round. In fact, Earth’s sphericity had been accepted as fact for nearly 1,800 years. The falsehood that the explorer’s contemporaries feared he would sail off the world’s edge emerged during 17th-century religious quarreling and was perpetuated by Washington Irving. The author of “The Legend of Sleepy Hollow” and “Rip Van Winkle,” Irving applied his fertile imagination to his History of the Life and Voyages of Christopher Columbus (1828), a biography with much fictional embellishment.
The first empirical demonstration of Earth’s sphericity was the Ferdinand Magellan–led circumnavigation of the globe, a grueling three-year journey (1519–1522) completed 30 years after Columbus set sail for the New World. But Magellan’s legacy has also been mythologized: Although the ship that completed the circumnavigation was indeed from his original fleet, Magellan had been killed in 1521 in the Philippines; the Great Circumnavigator, as Magellan is often called, actually made only a semicircle. Another myth, that a rival Portuguese explorer had discovered the Strait of Magellan, was dispelled by none other than Irving, in his Columbus biography.
Judaic, Christian and ancient Egyptian scriptures flatten Earth to a disk floating in a primordial ocean, a model latched onto by religious fundamentalists, pseudoscientists and false historians—including yarn spinner Washington Irving. In his truth-stretching History of the Life and Voyages of Christopher Columbus (1828), Irving depicts 15th-century Europeans as ignorant flat-earthers, putting them neatly in contrast to his scientifically astute hero. Actually, Europeans had accepted the planet’s shape as spherical 1,800 years earlier. In America, however, as late as the 1960s, history textbooks maintained that Columbus set out to prove the world is a globe.
Flat-earthers are still kicking around the planet, keeping alive the Flat Earth Society, an organization with 19th-century roots in the work of mainstream-science skeptic Samuel Birley Rowbotham (pseudonym Parallax), who based his beliefs loosely on a biblical model, along with a little creative liberty. Rowbotham’s 1865 tome Zetetic Astronomy: Earth Not a Globe holds that the disk-like world, centered at the North Pole, extends outward beyond the continents into an infinite arctic wilderness, and that the sun lies 4,028 miles from London. He also mused that the stars “may be particles of snuff in the box of a giant of a proportionately larger universe.”
“If any man could arrive at the exterior limit [of Earth],” wrote the Greek philosopher Plato in his Phaedo dialogue (c. 360 B.C.), “or take the wings of a bird and come to the top, then like a fish who puts his head out of the water and sees this world, he would see a world beyond.”
When Apollo 17 astronauts photographed Earth from space in 1972, they called the image The Blue Marble. The implication may seem belittling, as it equates our world to a tiny, round toy. (Einstein may have said, “God doesn’t play dice with the world,” but he never said anything about marbles.) But Plato, an early believer in Earth’s sphericity, had also demoted our planet to a knickknack—“one of those balls which have leather coverings in twelve pieces, and is decked with various colors”—when he imagined its overall aspect. While not leathery, Earth is quite colorful from space: The Blue Marble shows not only blue oceans but white clouds and ice caps, brown deserts and green forests. In 2012 NASA revealed Blue Marble 2012—an updated composite image of high-resolution photographs that adds the turquoise of Caribbean waters to the palette.
For much of history, Earth wasn’t considered a celestial object. An apparently flat, stationary mass, our planet seemed distinct from the tiny specks inching across the blackness. While astronomers began to debunk the flat-earth model two millennia ago, geocentrism, the belief that the heavens revolved around Earth, was obliterated only within the last 500 years, thanks to European astronomers Nicolaus Copernicus and Galileo Galilei. Yet, despite the scientific evidence, skeptical stragglers still wanted visual proof—a view from space, perhaps—to verify Earth’s shape and its place among the celestial brethren.
Seventeenth-century German astronomer Johannes Kepler imagined a spacefarer’s view of Earth from the moon in his 1634 novella Somnium (“The Dream”), considered the first work of science fiction. While many earthlings perceive a “man in the moon,” Kepler’s spacefarer imagines a rather naughty narrative developing among our planet’s continental shapes: “A human head…bending over to kiss a little girl…while her arm stretches backward and lures a leaping seducer.” In 1972 the Apollo 17 crew snapped the first photograph, The Blue Marble, of the fully illuminated Earth from space. It was the view that Kepler yearned for—leaping seducer and all.