Eratosthenes’ Origins and Measurements

Born around 276 BCE in Cyrene, now part of modern Libya, Eratosthenes eventually became the chief librarian at the esteemed Library of Alexandria, the pinnacle of learning in the ancient era. His fascination with geography and astronomy sparked his curiosity about the Earth's size.

One of his pivotal findings was related to a well in the Egyptian city of Syene, present-day Aswan. On the summer solstice, sunlight illuminated the bottom of the well, indicating that the Sun was directly overhead. In contrast, Eratosthenes noted that a vertical stick in Alexandria cast a shadow, revealing a difference in the Sun's angle.

Eratosthenes seized this opportunity to perform an ingenious experiment. He found that the angle of the shadow in Alexandria was approximately 7.2 degrees on the summer solstice. Knowing the distance between Alexandria and Syene was around 800 kilometers, he employed basic trigonometry to calculate the Earth's circumference.

The Calculation Technique

Eratosthenes applied a straightforward geometric approach for his calculations. He considered the distance between Alexandria and Syene as the arc length and treated the shadow's angle in Alexandria as a fraction of a complete circle (360 degrees). By calculating this proportion, he estimated the Earth's circumference to be about 39,375 kilometers, a figure remarkably close to modern measurements.

The Impact of Eratosthenes’ Work

Eratosthenes’ calculation marked a significant milestone in the evolution of science and mathematics. His accurate estimation underscored the importance of empirical observation and logical reasoning in understanding the natural world. Furthermore, his achievement showcased the collaborative nature of ancient scholarship, as he built his groundbreaking theory on data gathered by others.

Eratosthenes’ influence extends far beyond his time. His methods inspired future astronomers and geographers, including Ptolemy, and initiated further exploration into precise measurements across various scientific fields. The legacy of Eratosthenes continues to highlight the boundless human capacity for intellectual inquiry and exploration.

In Conclusion

Eratosthenes' measurement of the Earth's circumference is celebrated as a pinnacle of classical science. Through meticulous observations and innovative geometry, he accurately determined the planet's size, paving the way for subsequent generations to explore the cosmos. His legacy remains a powerful reminder that the quest for knowledge knows no boundaries.