Saturday, March 28, 2020

Dispelling Some Myths: The Earth is Flat

Once again a recently broadcast popular UK television programme promoted yet another “factoid”. A throw away comment, on camera, repeated the fiction that people in the 17th century believed the Earth was flat. Now I thoroughly enjoy the TV show, but in keeping with the theme of this series, this myth has been debunked so long ago I am agog that it was given credence. The media, in all its guises, has such a powerful hold on the imaginations of its subscribers that to allow these insidious “factoids” to creep into the popular subconscious would be unforgiveable.

Conceiving the Earth as a flat plane or disk has ancient roots, however. Many archaic cultures subscribed to a flat Earth model including the early Greeks (until the classical period[1]), the Bronze Age and Iron Age civilizations of the Near East until the Hellenistic period[2], India until the Gupta period[3], and China until the 17th century.

The idea of a spherical Earth first appeared in ancient Greek philosophy of the 6th century BC. Pythagoras of Samos and his contemporary Parmenides of Elea were both credited with having been the first to teach that the Earth was spherical[4]. Although the flat Earth model endured, in the early fourth century BC Plato was writing about a spherical Earth, and by about 330 BC his former student Aristotle provided empirical evidence for the spherical shape of the Earth.

Still not convinced the ancient Greeks knew the Earth was spherical, then consider the case of Eratosthenes of Cyrene. Chief librarian at the Library of Alexandria, Eratosthenes is best known for being the first person to calculate the circumference of the Earth without leaving home. By comparing angles of the mid-day Sun at two places, a known North-South distance apart. He knew that at local noon on the summer solstice in Syrene (modern Aswan, Egypt), the Sun was directly overhead. He then measured the Sun's angle of elevation at noon in Alexandria by using a vertical rod, known as a gnomon, and measuring the length of its shadow on the ground. Using the length of the rod, and the length of the shadow, as the legs of a triangle, he calculated the angle of the Sun's rays. This turned out to be about 7°, or 1/50th the circumference of a circle. Taking the Earth as spherical, and knowing both the distance (5,000 stadia) and direction of Syene, he concluded that the Earth's circumference was fifty times that distance. His calculation was remarkably accurate at 40,074 km (24,901 mi), which is 66 km (41 mi) different from the currently accepted polar circumference of the Earth.

Knowledge of the spherical Earth gradually began to spread beyond the Hellenistic world being supported by most scholars from AD 600s onwards. By the Early Middle Ages (between the 5th and 10th centuries) the belief in a flat Earth was almost non-existent. Certainly after AD 1400 most educated Europeans rejected the notion.

Despite the scientific facts, pseudoscientific flat Earth conspiracy theories are still championed by modern flat Earth societies. Rising to prominence from the middle of the 20th century, some adherents of these groups are serious, while some are not. The serious ones are typically motivated by religion, pseudoscience or conspiracy theories. Today, with the rise to prominence of social media, flat Earth theories have been increasingly advocated by individuals not connected with these larger groups. The myth of the flat Earth is a modern misconception, one that needs to be dispelled.


Notes:
1. The Classical period in Greece corresponds to most of the 5th and 4th centuries BC. The most commonly accepted range of dates begin with the fall of the last Athenian tyrant (Hippias, son of Peisistratos) in 510 BC to the death of Alexander the Great in 323 BC.
2. The Hellenistic period covers the period of Mediterranean history between the death of Alexander the Great in 323 BC and the emergence of the Roman Empire as signified by the Battle of Actium in 31 BC and the conquest of Ptolemaic Egypt the following year.
3. Corresponding to the ancient Indian Gupta Empire that existed from the mid-to-late 3rd century AD to AD 543.
4. Burkert, W. (1972), Lore and Science in Ancient Pythagoreanism, Cambridge, Massachusetts, Harvard University Press, p.306-308.

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