Dispelling Some Myths: The Earth is Flat

Once again a recently broadcast popular UK television programme promoted yet another ‘factoid’. On this occasion a throw away comment, on camera, repeated the fiction that people in the 17th century believed the Earth was flat. While the TV show is thoroughly enjoyable this ‘myth’ has been debunked so long ago that we were agog that it was given any credence. Yet, 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 we think is unforgiveable. So, in keeping with the theme of this series it is time to ‘Dispel Some Myths’.

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.

If you are still not convinced the ancient Greeks knew the Earth was spherical, then consider the case of Eratosthenes of Cyrene. Although he was chief librarian at the Library of Alexandria, Eratosthenes is best known for being the first person to measure 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. Eratosthenes described his arc measurement technique in a book entitled ‘On the measure of the Earth’, which has not been preserved. However, a simplified version of the method has survived as described by Cleomedes. He invites the reader to consider two Egyptian cities, Alexandria and Syene (modern Aswan) which he assumes are 5,000 stadia apart. He also assumes the simplified (but inaccurate) hypothesis that Syene was located precisely on the Tropic of Cancer and thus on the same meridian as Alexandria (Syene is actually about 3 degrees of longitude East of Alexandria).

Accepting the previous assumptions, Cleomedes writes that one can measure the Sun's angle of elevation at noon of the summer solstice in Alexandria, by using a vertical rod (a gnomon) of known length and measuring the length of its shadow on the ground. From this it is then possible to calculate the angle of the Sun's rays, which he claims to be about 7°, or 1/50th the circumference of a circle. Taking the Earth to be spherical, the Earth's circumference would be fifty times the distance between Alexandria and Syene and thus the meridian has a length of 252,000 stadia (39,060 to 40,320 km). To complicate things, however, a stadion (pl. stadia) is said to be equal to 600 Greek feet (podes) but the length of the foot varied in different parts of the ancient Greek world. Defining the length of a stadion therefore has been the subject of argument and hypothesis for hundreds of years. For ease, most people assume a value of between 155 and 160 metres, but this 5 m variation will induce an error on any calculated value of between −2.4% and +0.8%. Regardless, if one accepts that 1 Egyptian stadion is equal to about 157.7 metres, then Eratosthenes’ result is roughly 39,425 km, which is only 650 km less than the Earth’s real circumference of 40,075 km.

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. These beliefs emerged among a minority in Victorian times but really rose to prominence from about the middle of the 20th century onward. 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 increasing dominance of social media, flat Earth beliefs have been more widely advocated by individuals not connected with these larger groups. Whatever the source, however, it is most important to remember that the myth of a flat Earth is a modern misconception, not an ancient or Mediæval one, and as such really needs to be dispelled.

Endnotes:

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.