Twice a week we compile our most fascinating features and deliver them straight to you. Live TV. This Day In History. History Vault. Recommended for you. How the Troubles Began in Northern Ireland. Christopher Columbus. Eratosthenes was especially proud of his solution to the problem of doubling a cube, and is now well known for developing the sieve of Eratosthenes, a method of finding prime numbers. He recorded the details of this measurement in a manuscript that is now lost, but his technique has been described by other Greek historians and writers.
Eratosthenes was fascinated with geography and planned to make a map of the entire world. He realized he needed to know the size of Earth. Eratosthenes had heard from travelers about a well in Syene now Aswan, Egypt with an interesting property: at noon on the summer solstice, which occurs about June 21 every year, the sun illuminated the entire bottom of this well, without casting any shadows, indicating that the sun was directly overhead.
Eratosthenes then measured the angle of a shadow cast by a stick at noon on the summer solstice in Alexandria, and found it made an angle of about 7. He realized that if he knew the distance from Alexandria to Syene, he could easily calculate the circumference of Earth. But in those days it was extremely difficult to determine distance with any accuracy. Some distances between cities were measured by the time it took a camel caravan to travel from one city to the other.
But camels have a tendency to wander and to walk at varying speeds. So Eratosthenes hired bematists, professional surveyors trained to walk with equal length steps. They found that Syene lies about stadia from Alexandria. Eratosthenes then used this to calculate the circumference of the Earth to be about , stadia. Modern scholars disagree about the length of the stadium used by Eratosthenes.
The Earth is now known to measure about 24, miles around the equator, slightly less around the poles. We are republishing a lightly edited version on Popular Science in light of recent interest in the subject. Most recently, rapper B. Now that humanity knows quite positively that the Moon is not a piece of cheese or a playful god, the phenomena that accompany it from its monthly cycles to lunar eclipses are well-explained.
It was quite a mystery to the ancient Greeks, though, and in their quest for knowledge, they came up with a few insightful observations that helped humanity figure out the shape of our planet.
But—you say—ships do not submerge and rise up again as they approach our view except in Pirates of the Caribbean , but we are hereby assuming that was a fictitious movie series. Imagine an ant walking along the surface of an orange, into your field of view. This observation was originally made by Aristotle BCE , who declared the Earth was round judging from the different constellations one sees while moving away from the equator.
This would not have happened if the world was flat:. If you stick a stick in the sticky ground, it will produce a shadow. The shadow moves as time passes which is the principle for ancient Shadow Clocks. If the world had been flat, then two sticks in different locations would produce the same shadow:.
This is because the Earth is round, and not flat:. Eratosthenes BCE used this principle to calculate the circumference of the Earth quite accurately. To see this demonstrated, refer to my experiment video about Eratosthenes and the circumference of the Earth. Standing on a flat plateau, you look ahead toward the horizon. You strain your eyes, then take out your favorite binoculars and stare through them, as far as your eyes with the help of the binocular lenses can see. Next, climb up the closest tree—the higher the better, just be careful not to drop those binoculars and break their lenses.
Then look again, strain your eyes, and stare through the binoculars out to the horizon. The higher up you climb, the farther you will see.
0コメント