The Dawn of a Sphere: Unveiling the Discovery of Earth's Round Shape
The question of when humanity discovered that the Earth is round is a complex one, riddled with misconceptions and a gradual evolution of understanding. While pinpointing an exact date is impossible, we can trace the development of this knowledge through ancient civilizations, philosophical debates, and scientific advancements. It's important to note that even today, we know the Earth isn't a perfect sphere; it's more accurately described as an oblate spheroid, with the equatorial circumference slightly larger than the polar circumference.
Challenging the Flat-Earth Myth: Medieval Knowledge
One common misconception is that people in the Middle Ages believed the Earth was flat until Christopher Columbus's voyages. In fact, the Earth's true shape was well known in medieval Europe. Long before the Magellan-Elcano expedition completed its circumnavigation of the globe in 1522, no one doubted that, in theory, circumnavigation was possible. Educated people held a widespread belief in a round Earth as early as the Middle Ages. It’s a common misconception that Christopher Columbus, when he set sail for the East Indies, sought to prove Earth was round - in fact, he took it for granted. Neither he nor any other educated European feared that the Niña, the Pinta, and the Santa Maria would plunge off the edge into space. That was merely a legend, invented centuries later by the American writer Washington Irving.
Ancient Greece: The Cradle of Discovery
The earliest documented mention of the concept of a spherical Earth dates back to around the 5th century BC, appearing in the writings of Greek philosophers. Pythagoras in the 6th century BC and Parmenides in the 5th century BC stated that the Earth is spherical, and this view spread rapidly in the Greek world. However, attributing the discovery solely to Pythagoras is a misstep, likely popularized by Sir Thomas Little Heath. While Diogenes Laertius named several early figures, including Pythagoras, as the first to claim the Earth was round, the evidence is scant.
Plato and the Novel Idea
The earliest extant reference to the Earth being a globe comes from Plato's dialogue Phaedo (108e), around 400 BC. While Plato didn't invent the idea, his remarks suggest it was a novel and inchoate concept at the time. On that basis, we should date the genesis of the spherical earth to the early 4th century BC.
Aristotle's Empirical Evidence
By about 330 BC, Aristotle provided strong empirical evidence for a spherical Earth. Aristotle first discovered that during solar eclipses, Earth’s shadow always appeared on the Moon’s surface as a circle. He realized that only one object would invariably cast its shade in that shape: a sphere. And second, different stars and constellations are visible from different latitudes. If Earth were flat, everyone everywhere would be looking up at the same sky. As he marshalled evidence for sphericity, two astronomical observations proved especially compelling.
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Eratosthenes and the Circumference Calculation
The Earth's circumference was first determined around 240 BC by Eratosthenes. In the 3rd century BC, Hellenistic astronomy established the roughly spherical shape of Earth as a physical fact and calculated the Earth's circumference.
The Spread of Knowledge and the Occasional Setback
The Romans disseminated Aristotle’s ideas as far afield as India, which then transferred them to Islamic philosophers in the 8th century C.E. Western Europe lost sight of science through much of the medieval period, but the English monk Bede reintroduced the concept of a spherical Earth to Christendom around 725. However, the flat Earth theory returned during the Dark Ages, when Catholic scholars cited passages in the Bible that appeared to support the claim. Examples include references to "the four corners of the Earth" and a mountain summit from which "all the kingdoms of the world" are visible. These statements only make sense if Earth is flat, and at the time, the Bible was interpreted as literal truth.
Other Ancient Perspectives
While the Greeks are often credited with the discovery, other ancient civilizations also held beliefs about the Earth's shape.
Ancient China
In contrast to the gradual acceptance of a spherical Earth in the West, ancient Chinese scholars consistently described the Earth as flat. Chinese thought on the form of the Earth remained almost unchanged from early times until the first contacts with modern science through the medium of Jesuit missionaries in the seventeenth century. This perception remained unchanged until their encounters with Jesuit missionaries in the 17th century.
Vedic Texts
In the Vedic texts, Dyaus (heaven) and Prithvi (Earth) are compared to wheels on an axle, yielding a flat model. They are also described as bowls or leather bags, yielding a concave model.
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The Earth's Imperfect Shape: Later Refinements
Scientific theories which predicted deviation of Earth's shape from the sphere were proposed in he late 17th century. The correct theory was due to Newton. There was a competing theory predicting that equator is shorter than meridian (either by Descartes himself, or by his followers). To decide which theory is correct, several expeditions were sent by the French Academy to measure arcs of meridians. The first expedition did this in Peru (modern Equador) in 1735-45. in 1738. This result was one of the first major tests of the theory of universal gravitation.
The Oblate Spheroid
The realization that the figure of the Earth is more accurately described as an ellipsoid dates to the 17th century, as described by Isaac Newton in Principia. In the early 19th century, the flattening of the earth ellipsoid was determined to be of the order of 1/300 (Delambre, Everest).
Modern Perspectives and the Persistence of Flat-Earth Beliefs
Despite overwhelming scientific evidence, flat-Earth conspiracy theories persist. Since the 2010s, belief in a flat Earth has increased, both as membership of modern flat Earth societies, and as unaffiliated individuals using social media. In a 2018 study reported on by Scientific American, only 82% of 18- to 24-year-old American respondents agreed with the statement "I have always believed the world is round".
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