No shadow appeared in the well.Įratosthenes knew about the Syene well, and he also knew the sunshine in Alexandria, 804 km or 500 mi. At local noon on every summer solstice (earth's longest day and shortest night), the sun's rays went straight down the well, which meant Syene was perfectly lined up with those parallel sun rays. Generations of careful Egyptian land surveyors knew Syene was 5,000 stadia - ancient measurement units equivalent to 804 kilometers or 500 miles - south of Alexandria. That means the sun's rays hitting Eratosthenes' home in Alexandria are parallel to the sun's rays hitting Syene, a town far to the south, which today we call Aswan. Earth takes up only a small portion of the sun's circumference. Earth is so very small compared to the sun - roughly 109 earths could fit across the face (diameter) of the sun -that the sun's rays strike the earth nearly parallel to each other. Our sun is very far away from earth, 149,600,000 km on average. He did not know, but like any good mathematician and scientist, he intended to find out using his available resources. Library patron: "What is the circumference of the earth?".Imagine being the head librarian of the greatest library on the planet and a library patron asks you a simple question: He had no idea what the earth's circumference was. He knew the earth was round, but he did not know its size. It is squashed because of the sun's strong gravitational attraction, which makes it bulge out slightly at the equator.Įratosthenes, as head librarian of the great Library of Alexandria, had at his fingertips just about all the knowledge of the world at the time.
They knew it was a sphere, while today we know it is a squashed sphere, an oblate spheroid. Smart and educated people of the ancient world knew the earth was round.
Zoom math 500 showing steps how to#
Today we know how to measure circumference of many things, including earth, using many modern tools, but Eratosthenes did it with a well, the sun, and a stick.
Back in 240 B.C.E., a Greek named Eratosthenes calculated the circumference of the earth.
0 kommentar(er)
