- Published: 03 February 2010
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Dorothy Schaffner, age 11, of Omaha, Nebr., for her question;
Who discovered that the earth is a planet?
Each day the sun arrives in the east, swings around the sky and slips out of sight in the west. The same path is taken by the moon and stars. The earth seems to be at the center of a carousel with the heavenly bodies swinging around and around it. Until about 300 years ago, most people were sure that this was the truth. They were proud that their world was the hub of the universe, The idea made them feel important.
Nowadays, we know that the sky parades around because the earth is turning on its axis, This brings into view first one piece of sky, then another, The parade moves from east to west because the earth is forever turning towards the east. This idea gives us a pleasant feeling of belonging to a safe orderly family. The earth is but a smallish planet of the Solar System. The Solar System is a small part of a vast and orderly universe,
But people hate to give up an idea that makes them feel the. center of things, even when it is a burden. A few thinkers long ago suggested that the earth itself was turning, but the idea was unpopular. A Greek thinker named Herakleides suggested it in 395 B.C. Another early astronomer named Aristarchus expressed the same idea in 280 B.C. But people did not like the idea that the earth was one of several small bodies circling around the sun. They preferred to think that the universe turned around the earth and not the earth itself was turning,
The great Aristotle, who had an orderly mind, did not accept the idea that the earth was a turning planet. He taught that the earth was the hub of the universe and people were proud to accept his idea for many centuries. In the 16th Century, a polish priest named Nikolaus Kopernik was re‑studying some old charts of the heavens. He began to wonder if the Old Greek idea might not be true. In 1543, he published his ideas in a brilliant and upsetting book. He said that it might be true that the universe moved around the earth.
But ‑ we would get the same heavenly parade if the earth itself was turning around. He died in the year his book was published, before he had a chance to prove his theories. We know now that his brilliant ideas were correct.
His name has been Latinized and we know him as Copernicus, one of the greatest of all astronomers.
Proof of Copernicus theories had to wait over 50 years, for the invention of the telescope. This wonderful instrument which makes faraway things seem near was used by the Italian Galileo. In 1610, Galileo was using a telescope to get a closer look at the planets, the heavenly bodies that were called the wanderers because they made curly paths through the sky. He saw the moons of Jupiter, the rings of Saturn and the moon‑like phases of Venus. There was no doubt now that the earth was a planet, sister to several other planets all revolving around the sun. And that the earth itself was forever rotating towards the east, facing first one view and then another of the heavens.
There were still many people who tried to shout down Galileo’s proof that the earth was a planet. He was punished and even forced to contradict himself. But his last words show that he never gave up his own idea. In the midst of bitter argument he said, "Nevertheless, it revolves." The earth, he knew for sure, was a little planet, happily chugging around its parent the sun and spinning around on its axis to face first one side then another of the starry heavens.