THE SHAPE OF THE EARTH

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In the age of space travel, we all know the world is "round." But ancient civilizations had no way to measure the size or the shape of the Earth. So, they came up with their own imaginative explanations. For example:

" In the Cherokee nation, people believed that mud rose from under the waters and formed an island with four corners - the Earth. The Sun went underneath the island at night, and rose again the next day.

" Ancient Babylonians thought the Earth was inside a hollow mountain, floating on a sea. Everything - the sun, moon, sky, star, water - was inside this mountain

" Ancient Egyptians believed the whole Earth was part of their god, Keh. The stars were the jewels of a goddess in the sky and their god of air held her aloft.

" Ancient Hindus thought that the Earth was in an upside-down bowl, being carried by elephants. The elephants stood on the back of a turtle that was standing on top of a snake. What the snake stood on, they hadn't quite worked out.

" Polynesian creation stories set the Earth in a basket with a lid. A hole cut in the top by a god lets in light. The woven grass at night lets light peek through in the form of stars.

THE GREEKS KNEW

Many people believe that Columbus was the first to realize that the world is round. Actually, the round-Earth concept has been with us since ancient Greece.

The very early Greeks thought Earth was a flat disc floating on water. But in about 540 BC, the renowned mathematician Pythagoras proposed the theory that the world was a sphere. The concept had many supporters, including Aristotle.

ALL'S WELL…

In about 250 BC, Eratosthenes, librarian at the Library of Alexandria, even came up with a calculation of the Earth's spherical size.

He's heard that in midsummer in the town of Syene, Egypt, the noonday sun shone directly into a deep well. He measured and discovered that in Alexandria, 787 kilometers north, the angle of the sun was about 7.2 degrees on the same date. With these measurements, he computed the circumference of the Earth.

Amazingly enough, considering how he came up with the numbers and how little he had to prove them, Eratosthene's estimates were very close.

Another Scholar, Posidonius (135-151 BC) did something similar over a century later, using the bright star Canopus. He measured the angles of the star from the horizon in two locations to get a fairly accurate estimate of the Earth's circumference.

IN FOURTEEN HUNDRED AND NINETY TWO…

Fifteen years later, Christopher Columbus came along, trying to make his now famous voyage to Asia by going west. The decision of whether to fund his trip came down to analyzing the accumulation of estimates that had been gathered over the centuries.

Based on Eratosthenes' numbers, King Ferdinand believed that Columbus's fleet could never make it all the way to Asia: it was simply too far. He didn't see any reason to supply ships and crews only to have them die halfway from their goal.

Columbus used a ploy common in modern-day politics, marketing and engineering: If the numbers don't support your conclusion, find some numbers that do. He found another estimate by Ptolemy dating from about AD 150. It was completely erroneous, but estimated that the Earth was about half its true size… so Queen Isabella agreed to support the voyage.

Luckily for Columbus, America got in his way, or he never would have reached India or anywhere else. Crossing both the Atlantic and the Pacific combined would have been an impossible feat with the ships and supplies he had.

FLAT AND FAT

It wasn't until 1958 when the Vanguard I satellite took the first photographs of earth from space that scientists were able to determine the planet's exact shape. The photographs proved the world is round… right?

Well, not exactly. Scientists reported that the Earth is an oblate spheroid - i.e., it's not quite round.

Since the Earth spins, it gets a slight bulge near the equator. Near yes, but not (as you might suspect) exactly on the equator.

Because of this bulge, the Earth is flattened very slightly on either end. Its circumference at the equator is 24,902 miles, and the circumference around the poles is 27 miles less than that: 24,875 miles. Not a big deal really - if the world were the size of a basketball, it would be more perfectly round than a real basketball is. But still, after guessing for so long, scientists can't resist the opportunity to get it exactly right.

THE WORLD IS PEAR SHAPED

Ironically, toward the end of his life, Columbus came to believe the Earth was shaped like a pear. He developed this theory during his third voyage to the New World. When he was sailing west near the equator, he noticed that the North Star made a wider circle around the Pole than it did when he was sailing in more temperate latitudes.

From this he deduced that he had been sailing gradually up hill and therefore closer to the sun, which explained why the weather was getting warmer. "I have come to the conclusion," he wrote, in a letter to Queen Isabella, "… that the Earth is not round, but of the form of a pear… Where the stalk grows being the highest and nearest the sky."

Columbus believed that if he sailed far enough, he would eventually reach the Garden of Eden, which is located in the pear's stalk. (Ripley's Believe It or Not.) []