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Been There - the other causes the apparent position of the...

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Been There, Done That: Aristarchus of Samos The idea of Copernicus was not really new! A sun-centered Solar System had been proposed as early as about 200 B.C. by Aristarchus of Samos ( Samos is an island off the coast of what is now Turkey). However, it did not survive long under the weight of Aristotle's influence and "common sense": 1. If the Earth actually spun on an axis (as required in a heliocentric system to explain the diurnal motion of the sky), why didn't objects fly off the spinning Earth? 2. If the Earth was in motion around the sun, why didn't it leave behind the birds flying in the air? 3. If the Earth were actually on an orbit around the sun, why wasn't a parallax effect observed? That is, as illustrated in the adjacent figure, stars should appear to change their position with the respect to the other background stars as the Earth moved about its orbit, because of viewing them from a different perspective (just as viewing an object first with one eye, and then
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Unformatted text preview: the other, causes the apparent position of the object to change with respect to the background). The first two objections were not valid because they represent an inadequate understanding of the physics of motion that would only be corrected in the 17th century. The third objection is valid, but failed to account for what we now know to be the enormous distances to the stars. As illustrated in the following figure, the amount of parallax decreases with distance. Parallax is larger for closer objects The parallax effect is there, but it is very small because the stars are so far away that their parallax can only be observed with very precise instruments. Indeed, the parallax of stars was not measured conclusively until the year 1838. Thus, the heliocentric idea of Aristarchus was quickly forgotten and Western thought stagnated for almost 2000 years as it waited for Copernicus to revive the heliocentric theory....
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