Join thought-provoking conversations, follow other Independent readers and see their replies. Want to bookmark your favourite articles and stories to read or reference later? Start your Independent Premium subscription today. More about Business Insider Ancient Greece. Already subscribed? Log in. Forgotten your password? Want an ad-free experience? 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.
The greater a concentration of mass is, the stronger its gravitational pull, "creating bumps around the globe," says geologist Joe Meert at the University of Florida in Gainesville. Earth's shape also changes over time due to a menagerie of other dynamic factors. Mass shifts around inside the planet, altering those gravitational anomalies. Mountains and valleys emerge and disappear due to plate tectonics. Occasionally meteors crater the surface. And the gravitational pull of the moon and sun not only cause ocean and atmospheric tides but earth tides as well.
In addition, the changing weight of the oceans and atmosphere can cause deformations of the crust "on the order of a centimeter or so," notes geophysicist Richard Gross at the Jet Propulsion Laboratory in Pasadena, Calif. Moreover, to even out Earth's imbalanced distribution of mass and stabilize its spin, "the entire surface of the Earth will rotate and try to redistribute mass along the equator, a process called true polar wander," Meert says. That was thanks to scientists, philosophers and mathematicians who, as early as around B.
However, Columbus ran into resistance when he tried to get funding for his landmark journey for a different reason. After years of negotiation and argument over the actual length of the proposed journey, he finally convinced Ferdinand II of Spain and his wife Isabella to finance the expedition. A map of the four voyages of the Italian navigator, Christopher Columbus. Crucially, he claimed that when the explorer told Spanish geographers the earth was not actually flat, they refused to believe him, even questioning his faith and endangering his life.
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. 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.
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