Greater than 2,200 years earlier than satellites, GPS and house missions revealed the Earth’s true measurement, an historical Greek scholar calculated the planet’s circumference utilizing nothing greater than a stick, daylight and primary geometry. Round 240 BCE, Eratosthenes, the chief librarian of the Library of Alexandria, carried out one in every of historical past’s most good scientific experiments. By evaluating the lengths of shadows in two Egyptian cities, he produced an estimate of the Earth’s circumference that got here astonishingly near the fashionable measurement, proving that cautious statement and arithmetic might unlock the secrets and techniques of the pure world.
How did an historical Greek scholar calculate the planet’s circumference
In keeping with the American Bodily Society, Eratosthenes had heard that in Syene (modern-day Aswan) on the summer time solstice, the Solar stood instantly overhead at midday. At that second, daylight reached the underside of deep wells, and upright objects forged nearly no shadow.Curious whether or not the identical was true elsewhere, he noticed the Solar in Alexandria, round 800 kilometres to the north, at the very same time. Not like in Syene, a vertical stick there forged a noticeable shadow. Measuring the angle between the stick and its shadow, he discovered it to be about 7.2 levels.This easy distinction revealed that the Earth’s floor was curved. If the planet had been flat, each cities would have skilled the Solar on the identical angle.
How a easy calculation measured a whole planet
Eratosthenes knew the approximate distance between Alexandria and Syene, estimated at about 5,000 stadia by skilled surveyors who travelled the route.He realised that the 7.2-degree angle represented one-fiftieth of a whole circle as a result of 7.2 × 50 equals 360 levels. If the gap between the 2 cities was one-fiftieth of the Earth’s circumference, multiplying 5,000 by 50 gave a complete circumference of about 250,000 stadia. He later refined the determine to 252,000 stadia, making it simpler to divide into levels.Regardless that the size of the stadium utilized by Eratosthenes was not constant, historians have taken it under consideration and calculated the size to be someplace between 39,000 and 40,000 kilometres. The true circumference of the Earth’s equator is 40,075 kilometres.
Why Eratosthenes’ experiment stays a scientific masterpiece
The success of Eratosthenes’ calculation trusted cautious statement, logical reasoning and a sound understanding of geometry quite than superior know-how. His technique assumed that daylight reaches the Earth in practically parallel rays and that the Earth is spherical, concepts that proved appropriate.Whereas small inaccuracies arose as a result of Alexandria and Syene aren’t completely aligned north to south and the precise distance between them was solely an estimate, the consequence stays one of many biggest scientific achievements of the traditional world.Greater than 2,200 years in the past, the sizes of the Earth had been calculated utilizing satellites to astounding accuracy. Nevertheless, the contributions of Eratosthenes proceed to be revered even as we speak as an everlasting lesson of how one can use curiosity, statement, and math to unravel mankind’s biggest secrets and techniques.
