Ancient Knowledge of a Round Earth: How Early Greeks Discovered the Shape of the Earth

Humans have long wondered about the Earth's shape, and the ancient Greeks were among the first to accurately determine that it was round. This article explores the pivotal contributions made by figures such as Eratosthenes and Thales of Miletus, and how their observations and mathematical computations helped lay the foundation for our modern understanding of the world.

1. Knowledge of the Earth's Shape in Ancient Greece

While the general populace may not have pondered the shape of the Earth, scientifically educated individuals were well aware of its round form. The knowledge of the Earth's roundness was not a mere guess, but rather a well-supported conclusion derived from careful observation and mathematical analysis.

1.1 Thales of Miletus (624-546 BCE)

Thales of Miletus, an Ionian philosopher, made one of the earliest known attempts to measure the Earth's diameter. By comparing the length of shadows cast by towers in Greece and in Sudan at the summer solstice, he was able to make an accurate estimation of the Earth's size. This early insight demonstrated the power of geometrical and observational methods.

1.2 Eratosthenes (276-194 BCE)

Eratosthenes, the Chief Librarian of the Library of Alexandria, is perhaps the most famous ancient Greek for his work on determining the Earth's circumference. Using a simple yet ingenious method, he calculated the Earth's radius with remarkable accuracy.

2. Eratosthenes' Method and Calculations

Eratosthenes conducted an experiment in which he observed the angle of the sun's rays at two different locations: Alexandria and Syene (modern-day Aswan, Egypt). He realized that the sun shone directly into a well in Syene at noon on the summer solstice, indicating that the Earth was curved from his vantage point in Alexandria. By comparing the angle of the sun's rays and the known distance between the two cities, he estimated the circumference of the Earth.

His calculations were based on the knowledge that the distance between Alexandria and Syene was about 5,000 stadia (an ancient Greek unit of measurement). Using this information, he concluded that the Earth's circumference was approximately 250,000 stadia, which translates to roughly 40,000 kilometers. This result was remarkably close to the actual circumference of the Earth, which is approximately 40,075 kilometers.

3. The Process of Knowledge Diminishment

The method of observing and calculating the Earth's shape and size was not lost immediately. However, over time, this knowledge faced challenges and was sometimes replaced by more politically or religiously convenient beliefs.

3.1 Early Medieval Times (300-1100 CE)

About 300 years after Eratosthenes, the chief librarian of the Great Library of Alexandria, Claudius Ptolemy, advocated for the flat Earth theory. His reasoning was based on the prevalent astrology at the time, which held that the Earth had to be flat to align with astrological predictions. This shift in belief was influenced by the desire to maintain the status quo and the influence of superstitions.

3.2 The Medieval Period (1100-1500 CE)

During the medieval period, the focus shifted again when the Christian world sought to maintain itself on par with the developing Muslim world. The pope commissioned Thomas Aquinas, a renowned scholar, to reconcile the conflicting views of Eratosthenes and Ptolemy. Aquinas, influenced by his former professor Albert von Boellstadt, an astrologer, concluded in favor of Ptolemy's flat Earth theory, thus solidifying this belief within Christian scientific thought.

4. The Rediscovery and Reaffirmation of Eratosthenes' Work

Thankfully, Eratosthenes' work did not remain forgotten for long. Around the time of Christopher Columbus, his writings were rediscovered. Columbus used these insights to argue with Queen Isabella for permission to sail west and discover India. This rediscovery helped reignite interest in the round Earth theory and paved the way for further exploration and discovery.

5. Conclusion

The ancient Greeks, through the minds of Thales and Eratosthenes, recognized the Earth's round shape and provided mathematical evidence to support this concept. Despite periods of temporary setback, their findings have stood the test of time and contributed significantly to our understanding of the world. As we continue to explore and understand the cosmos, it is crucial to remember the scientific and intellectual achievements of the past that laid the groundwork for our current understanding of the universe.