Looking back in history, the ancient Greeks were the first to start developing theories about the design of the Universe.
Previous observations of the moon had already led to the knowledge that the Earth was round. When coupled with Plato’s assertion that the sphere was the perfect geometrical shape, the original Geocentric, or Earth-Centered view of the Universe was formed.
While many earlier observers in history believed the heavens were a giant bowl covering the Earth, this new philosophy, expounded by Astronomer Eudoxus and Philosopher Aristotle in the 4th century BC, said the sun, moon, and planets hung on concentric spheres, all surrounding the Earth.
Although helpful to ancient people trying to make sense of an unknown universe, this model did not help in properly tracking planets, the moon, or stars. Still, with few refinements, it remained the predominant scientific view of the Universe for another 600 years.
In the 2nd century BC, Claudius Ptolemaeus (Ptolemy), a Roman astronomer working in Egypt added epicycles to the Geocentric model. He said that the planets moved in perfect circles, attached to perfect spheres, that all rotated around the Earth. While it was wrong, this theory could, at least, predict the paths of the planets fairly well. This view remained in use for another 1400 years.
In the 16th century, Nicolaus Copernicus, a Polish Astronomer, tiring of the cumbersome and imprecise nature of the Ptolemaic Model, began working on a theory of his own. He theorized that the Sun was at the center of the Universe, and that the Earth and other planets revolved around it.
The Copernican Model of the Universe, while still incorrect, did three main things. It explained the prograde and retrograde motions of the planets. It took the Earth out of it’s spot as the center of the universe. And, it expanded the size of the Universe. (In a geocentric model, the size of the Universe is limited so that it can revolve once every 24 hours, or else the stars would get slung off due to centrifugal force.
While it was a major step in the right direction, Copernicus’ theories were still quite cumbersome and imprecise. His book, On the Revolutions of the Heavenly Bodies, which was published as he lay on his deathbed, was still a key element in the beginning of the Renaissance and the Age of Enlightenment.
Assignment
History: Read more about Claudius Ptolemaeus (Ptolemy) and Nicolaus Copernicus. Don't forget the discussion Forum.Next lesson, Seeing is Believing, more History of Astronomy.
Second Lesson > Seeing Is Believing > Lesson 2, 3, 4, 5, 6, 7, 8, 9, 10
