Ancient Greece

Reading Level
     edHelper's suggested reading level:   grades 9 to 11
     Flesch-Kincaid grade level:   9.1

     challenging words:    sun-centered, angular, heliocentric, geometry, mathematics, disposal, penned, invalid, astronomy, astronomer, groundbreaking, calculate, hypothesis, incorrect, scholar, draft
     content words:    De Revolutionibus

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By Vickie Chao

1     In history, we all have heard that a Polish astronomer named Copernicus (1473 - 1543) proposed the idea that the Earth rotates and revolves around the sun. That groundbreaking heliocentric (sun-centered) theory became one of the most important scientific hypotheses ever made. But, surprisingly, it was nothing new! More than 1,700 years earlier, a Greek astronomer named Aristarchus (310 B.C. - 230 B.C.) made the same claim. So he was, in fact, the first person to correctly state what we know is true today.
2     Aristarchus was a brilliant scholar from Samoa, Greece. He specialized in both mathematics and, of course, astronomy. During his lifetime, this great scientist probably penned several publications. Yet, sadly, only one -- On the Sizes and Distances of the Sun and Moon -- has survived to the present time.
3     In On the Sizes and Distances of the Sun and Moon, Aristarchus attempted to use geometry to calculate the relative distances of the sun and the moon (from the Earth), as well as the relative sizes of these two planets. Based on his findings, he concluded:

      1. At the moment that we can only see half of the moon (as it appears to us in its phase of first or last quarter), its angular distance from the sun is 87 degrees.

2. The diameter of the sun is 18-20 times the diameter of the moon.

3. Likewise, the distance of the sun from the Earth is 18-20 times the distance of the moon from the Earth.

Paragraphs 4 to 6:
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