Lesson 21: This lesson is on Aristotle’s idea of how the solar system is arranged. He had a wrong idea about it unfortunately, and his wrong idea was thought to be true for almost 2,000 years. He thought that the earth was the center of the universe, and that the sun, moon, planets and stars all revolved around it at different speeds. He thought the universe was made up of a stack of spheres cut in half, like a bunch of bowls stacked inside each other, with the earth in the middle, and the planets, sun, and stars all sort of resting along the brims of the various “bowls.” They traveled along the tops like a track, he thought. Each planet had its own sphere and moved at its own pace. This idea that the earth is the center of the universe is called geocentric.
Lesson 22: There was another philosopher who lived right after the time of Aristotle, and his name was Aristarchus (air-is-tar-cus). He got lots of things wrong, and he wasn’t nearly as popular as Aristotle, but he got one this right that Aristotle got wrong! This was that the sun is actually in the center of the universe, not the earth. This is known as Helio-centric, and Helio is the Greek god of the sun. Because he thought the sun was is the middle of the solar system, and if they earth goes around it, it must be true then that the earth rotates, which is what makes day and night. He would have also known (probably) that the moon goes around the earth. He got wrong, however, that the stars don’t rotate around the sun, but rather they stay in a fixed position. It’s just that as the earth revolves around the sun, we are able to see different stars because the earth is in a new place for the different seasons. Aristarchus’ ideas were not confirmed to be true until Copernicus argued in favor of them in 1543! A good lesson here is not believe in someone’s ideas just because they are popular or smart. Even really smart scientists get things wrong.
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