Appearances, however, can be deceiving. Planet Earth is not, in fact, perfectly round. This is not to say Earth is flat. Well before Columbus sailed the ocean blue, Aristotle and other ancient Greek scholars proposed that Earth was round. This was based on a number of observations, such as the fact that departing ships not only appeared smaller as they sailed away but also seemed to sink into the horizon, as one might expect if sailing across a ball says geographer Bill Carstensen of Virginia Tech in Blacksburg.
Isaac Newton first proposed that Earth was not perfectly round. Instead, he suggested it was an oblate spheroid—a sphere that is squashed at its poles and swollen at the equator. He was correct and, because of this bulge, the distance from Earth's center to sea level is roughly 21 kilometers 13 miles greater at the equator than at the poles.
Instead of Earth being like a spinning top made of steel, explains geologist Vic Baker at the University of Arizona in Tucson it has "a bit of plasticity that allows the shape to deform very slightly. The effect would be similar to spinning a bit of Silly Putty, though Earth's plasticity is much, much less than that of the silicone plastic clay so familiar to children. Our globe, however, is not even a perfect oblate spheroid, because mass is distributed unevenly within the planet.
Your email address will not be published. Leave a Reply Cancel reply Your email address will not be published. Alexandria was not due north of Syene, but 2 degrees of longitude off. Syene was not precisely on the Tropic of Cancer but 39 minutes of latitude north of it.
The distance between the cities was an estimate. The Earth is not a perfect sphere, but an oblate spheroid flattened at the poles. And we don't know today the exact size of the measurement unit Eratosthenes was using when he came up with the final figure of , stades.
We know he knew it was just a rough estimate, because he adjusted his initial number of , upward by 2, -- or 0. So how big is , stades? Depending on which classical source you trust, it's somewhere between 24, and 27, miles. Possibly the first to propose a spherical Earth based on actual physical evidence was Aristotle B. Around this time Greek philosophers had begun to believe the world could be explained by natural processes rather than invoking the gods, and early astronomers began making physical measurements, in part to better predict the seasons.
The first person to determine the size of Earth was Eratosthenes of Cyrene, who produced a surprisingly good measurement using a simple scheme that combined geometrical calculations with physical observations. Eratosthenes was born around B. He studied in Athens at the Lyceum. Around B.
Known as one of the foremost scholars of the time, Eratosthenes produced impressive works in astronomy, mathematics, geography, philosophy, and poetry. 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.
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