The planet Earth is a sphere. This is a common fact for you and me. However, what makes me wonder is, how did people back in time prove that Earth has a spherical shape when they had no aid of technology such as satellites to provide measurements and data?
With this question in mind, I briefly learned about how the ancient Greeks used simple tools to prove the hypothesis of Earth is round and even calculated the circumference of Earth with just a stick.
Greek philosophers are commonly credited for the discovery of Earth’s true geometric shape, with the two major and most well-known contributors being Aristotle and Eratosthenes.
Over 2,000 years earlier in Greece, Aristotle’s observations of stars made it evident that Earth was round. He stated that since we see variations of star sequences depending on our locations, the Earth must be circular. Additionally, if the Earth was flat, which is what the majority of the population believed in ancient Greece, we would see identical sets of stars from any position on Earth at any time.
Adding on to this argument, the Greek scholar Eratosthenes soon provided calculations of the Earth’s approximated circumference, which was proven by satellites launched in the mid-20th century to be correct.
Eratosthenes’ methodology was crude. Noticing the sun casts shadows of different length on objects at different locations on Earth at the same time, he observed shadows of sticks at noon in two Egyptian cities and measured the difference in degrees. With the distance between those two cities known, he was able to use trigonometry to estimate the circumference of Earth. It is now verified that Eratosthenes’ calculations only differ from the exact measurements of Earth’s actual circumference by 2%.
From our perspectives today, the fact that Earth is round might seem like common sense. Nonetheless, it is stunning how the ancient Greeks were able to use such “simple” approaches to prove hypotheses that may have seemed to be ravings back in time.
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