Columbus and the Flat Earth Myth: Navigating Between Errors and Truth, Defying the Trade Winds

Did people in Columbus's time believe the Earth was flat?

No, the Earth's sphericity had been known to Western scholars since ancient Greece. The Spanish commission initially rejected Columbus's project not because of Earth's "flatness," but because correct calculations showed the distance was too great. Columbus presented flawed calculations, but his intuition about the trade winds proved correct.

Contrary to a widespread belief, by the time of Christopher Columbus (who lived between 1451 and 1506), most Western scholars did not believe the Earth was flat.

The ancient Greeks, in particular, had gathered evidence of the Earth's sphericity since classical antiquity. This scientific discovery was made possible through actual experiments, empirical observations, and the use of reason. According to Theophrastus, it was Parmenides, shortly after 500 BC, who first argued that the Earth was spherical. His reasoning was based on the philosophical idea of a "perfect form," alluding to the notion that the only shape capable of remaining naturally in equilibrium was the sphere. Plato also reached the same conclusion: the sphere is the perfect solid, immutable and symmetrical from all sides. The Earth, placed at the centre of the Universe, could only be spherical.

Even though driven by philosophical motivations, the ancient Greeks were right: gravity, "pushing" equally from all sides, causes celestial bodies to assume an approximately spherical shape, where mass is distributed along equipotential surfaces.

The Experiment of Eratosthenes

One of the most famous experiments supporting the Earth's sphericity was presented by Eratosthenes of Cyrene (approximately 276–194 BC). This historical example shows how mathematics and physics can measure seemingly inaccessible phenomena. The story goes that Eratosthenes measured the Sun's angle of elevation at noon in the Egyptian city of Syene (now Aswan) and, simultaneously, in Alexandria, Egypt, which lay further north. He noticed that in Syene the Sun was directly overhead at noon, while in Alexandria the Sun's angle was about 7.2 degrees from the vertical — approximately 1/50 of a full circle.

With this information, Eratosthenes reasoned that the angular difference between Syene and Alexandria was attributable to the curvature of the Earth. Assuming the Earth was spherical, he used the angular difference and the distance between Syene and Alexandria to estimate its circumference.

From this experiment, Eratosthenes deduced that the Earth's circumference must be 50 times the distance between Alexandria and Syene, therefore 250,000 stadia, equivalent to approximately 39,000 km. We know today that the Earth is not a perfect sphere and is elongated at the equator relative to the poles, so much so that it is impossible to provide a standard length for the Earth's circumference. For this reason, the universally used average circumference figure is 40,075 km. If we compare this figure with Eratosthenes' circumference, we can immediately recognise the extraordinary precision with which he calculated the distance using a simple experimental apparatus.

Three Observations on the Earth's Sphericity

Beyond the philosophical conception of sphericity proposed by Plato and the experiment by Eratosthenes, the ancients made three simple observations that validated the thesis of a spherical Earth:

• Ships moving away at sea progressively disappear behind the Earth's curvature, highlighting its convexity.
• When approaching a coast, mountains are seen first and then the beach.
• Every lunar eclipse shows the Earth's profile: since eclipses occur at any time, meaning for any angle of the Earth's rotation, and the shadow's profile is always a circular arc, one can deduce that the body casting the shadow — the Earth — is spherical, since it is the only body capable of always projecting a circular shadow.

Columbus's Scientific Errors

In the 15th century, the spice trade was an extremely lucrative and desirable activity for all governments. Christopher Columbus, in the service of the Spanish monarchs Isabella and Ferdinand, proposed a new trade route to reach the Indies: sailing westward across the Atlantic Ocean, where no one had ever ventured, to arrive first and surpass the Portuguese in trade.

The mission was so innovative, dangerous, and audacious that the Queen had to appoint an inquiry commission to establish its feasibility and to allocate the necessary funds. The commission, on its first review, rejected the mission — not because of the supposed flatness of the Earth, but because of the excessive distance separating Spain from the Indies along the westward route.

The project was subsequently approved, partly due to a series of errors in scientific calculations made by Christopher Columbus and presented to the commission. Columbus, probably aware of his errors but eager to get the project approved, presented the commission with entirely wrong calculations:

• Among the countless available estimates of the Earth's circumference, Columbus took the lowest estimate, the one most favourable to his expedition's approval
• Columbus used the "Italian mile" or "Roman mile" instead of the "nautical mile," which would have been the correct unit. The Italian mile was shorter than the nautical mile we use today. An Italian mile corresponded to approximately 1.48 kilometres, while the modern nautical mile is standardised at 1.852 kilometres, allowing him to save on the calculations presented to the queen
• He began performing calculations starting from the Canary Islands, the westernmost part of Spain

In this way, Columbus, unlike Eratosthenes, estimated the approximate circumference of the Earth at only 25,000 km, and the distance to travel to reach Japan at less than 4,000 km — a voyage within the range of the caravels of the time. The actual distance to travel was over 19,000 km. Columbus and his men, due to the error committed, were destined to die of thirst in the middle of the ocean. What saved Columbus and his crew was his greatest "error." At the time, no one knew that between Europe and Asia, to the west, lay the American continent!

Columbus's Scientific Intuition: The Trade Winds

Despite the numerous inconsistencies presented by Columbus, one accurate and favourable scientific fact was presented to the commission: The existence of the trade winds that would push Columbus's caravels towards the Indies with ease.

The trade winds are a type of prevailing winds that blow constantly from east to west in the tropical and subtropical regions of the Earth's atmosphere. These winds take their name from the word "trade," derived from "trader" or "merchant," because they were widely used by sailors and merchants during trade routes between Europe, Africa, Asia, and the Americas. The most important characteristics of the trade winds that contributed to the discovery of America are:

• Direction: The trade winds blow from east to west. In the Northern Hemisphere, they are known as the "Northeast Trade Winds" and generally blow from northeast to southwest. In the Southern Hemisphere, they are called the "Southeast Trade Winds" and blow from southeast to northwest.
• Latitude: The trade winds are found primarily between 20 and 30 degrees of latitude in both the Northern and Southern Hemispheres. These latitudes can vary slightly in response to seasonal atmospheric changes.
• Origin: The trade winds are generated by differential heating between the equator and the cooler tropical regions. Warm, moist air rises in the equatorial area, creating a zone of low pressure. Cooler, denser air then moves from the tropics towards the equator to fill this void, generating the trade winds.
• Regularity: The trade winds are known for their constancy and regularity, although they can undergo some seasonal variations. This regularity made them important for maritime navigation and trade route planning, as historical sailors used them to travel between continents.

The trade winds played a significant role in Columbus's discovery of America and continued to influence the routes of subsequent explorers, including Hernan Cortes, Francisco Pizarro, and others who explored and conquered the lands of Central and South America. These constant winds facilitated maritime voyages and the expansion of European knowledge of the New World.

In summary, the trade winds were fundamental in enabling European explorers to cross the Atlantic Ocean and discover America with the aid of caravels. These constant winds provided reliable routes for transoceanic voyages and contributed significantly to the mapping and knowledge of the American continent.

FAQ

Did Columbus really believe the Earth was flat?

No, Columbus knew the Earth was spherical. The idea that people in the Middle Ages believed in a flat Earth is a modern myth. The Spanish commission initially rejected Columbus's project because correct calculations showed the distance was too great for the caravels of the time.

How accurate was Eratosthenes' calculation of Earth's circumference?

Remarkably accurate: Eratosthenes calculated approximately 39,000 km, while the actual average value is 40,075 km. With simple experimental apparatus and shadow measurements, he achieved an error of less than 3%. This demonstrates the power of the scientific method.

What are trade winds and why were they important for Columbus?

Trade winds are constant winds that blow from east to west in tropical regions, generated by differential heating between the equator and the tropics. For Columbus, they were fundamental because they pushed caravels westward predictably, making the Atlantic crossing possible.

What scientific errors did Columbus make in his calculations?

Columbus underestimated Earth's circumference (25,000 km instead of 40,000), used the wrong unit of measurement (Italian miles instead of nautical miles), and chose the lowest available estimate. He calculated the distance to Japan at less than 4,000 km instead of the actual 19,000 km.