Our Island Universe: Two Small Pieces of Glass Ushered in a Revolution in Science
Between January 7 and January 13, 1610, a series of observations was made that would forever change how we would view the cosmos. The observer detailed in this log book a discovery made using a relatively new invention at that time. The observer had discovered four small, point sources of light very close to the (giant) planet Jupiter. On January 10, one of them disappeared for a short period. The observer attributed the disappearance of the object as being hidden behind Jupiter. Given his extensive observations, he was now forced to conclude that these four points of light were orbiting Jupiter and not Earth. The observer, Galileo Galilei, and his two small pieces of glass would usher in a scientific revolution that reverberates to this day.
Until this discovery, and for some 1,500 years prior to Galileo, our ancestors accepted the model [Earth is] at the center of it all ...that originated with Aristotle and was fortified by Claudius Ptolemy.
The idea of a Sun-centered solar system did not originate with Copernicus even though we often give him credit. In fact, there is now evidence that Aristarchus of Samos some 2,200 years ago proposed a Sun-centered model. He even put the planets in their correct order from the Sun. ...This idea would not resurface until the 16th century when a Polish astronomer, Nicholaus Copernicus, revived the idea of a Sun-centered cosmos....
In the same time frame that Galileo was making his observations, Johannes Kepler was forced to also reconsider Aristotelian cosmology. ...While Copernicus published his Sun-centered model in 1543, it was largely ignored as his model made no better predictions than Ptolemy’s. Why? He still had “perfect circles” for the orbits of planets. Kepler, using Brahe’s exquisite observational data, found “perfect circles” didn’t fit the data, but instead — elliptical orbits did — and Kepler’s first law of planetary motion was born. Even though Copernicus’s heliocentric model predates Galileo’s discovery by nearly seven decades, it was Galileo and his telescope that provided the evidence in support of this idea. Using the new technological invention of the time — a telescope — Galileo observed the moons of Jupiter, that Venus goes through the same set of phases our Moon goes through, that there are craters on our Moon, and that the Sun has spots on it, all with his 2-inch-diameter telescope. These observations are incompatible with the philosophical Earth-centered model of Ptolemy and Aristotle. And so away went the geocentric universe and the idea of the cosmos as “perfection personified.”