February 15 marks Galileo’s 461st birthday.
The man has a long list of accomplishments in the field of astronomy attributed to his name, including improving and developing the telescope, discovering sunspots, and proving that earth was not the center of the universe.
One of Galileo’s most widely-known accomplishments is the discovery of Jupiter’s four largest moons, also known, aptly, as the Galilean Moons. Their names—Ganymede, Io, Callisto, Europa—are widely known, but the consequences of their discovery are more significant than you might think. Because Galileo was an early developer of the telescope at a time when the science of astronomy was experiencing radical progress, he sometimes had the luxury of pointing his spyglass skyward and stumbling on a previously undiscovered object. To wit, the astronomer actually observed Neptune in 1612 and marked it in his notes as an insignificant, dim star. And while you can imagine Galileo’s initial discovery of these moons as being similarly haphazard, he quickly realized something significant had happened.
Upon his first observation, three of the Galilean Moons were arranged in a straight line extending outward from Jupiter.
Not altogether unremarkable in a sky full of bright objects, but it was the first indication that there was something unique about these spots. “Three fixed stars, totally invisible by their smallness,” Galileo remarked in his initial notes. After observing these objects on subsequent nights, he realized that their positions were changing relative to Jupiter, in ways that did not make sense for "fixed stars.” Within days, he realized that the three spots he initially observed were orbiting Jupiter, and that there was indeed a fourth object moving in conjunction with the others.
It’s an interesting enough discovery, but it was also inevitable. In fact, another astronomer, Simon Marius, working independently of Galileo around the same time, also discovered these moons and gave them the names we know them by today (Galileo had initially named them “The Medicean Stars” in honor of his patron-to-be).
The reason that this discovery really altered the course of astronomy is twofold.
The first is that it disproved once and for all old Aristotelian notions about the cosmos. Aristotle believed that every object in the night sky orbited around the earth, and Jupiter’s moons were the first objects to be observed not following this pattern of behavior. The second reason is that it would set Galileo down a path toward acceptance of the heliocentric model of the universe (i.e., the Sun being the center of the universe), which famously led to him being tried and found guilty of heresy, besides influencing a great deal of his later work.
These dual pillars of significance are actually parts of the same idea on a deeper level. Old notions about the universe (including geocentricism) emphasized the importance of the earth, and led people to believe that they were at the center of the universe. The fact that Jupiter had a few moons rotating around it did not directly contradict the geocentric model, but it laid a framework for a more holistic way of thinking about the cosmos. That is, it exposed the scale of our universe as being something much larger and more complicated than our own planet or even our own solar system. Carl Sagan famously pointed to a photo of the earth sent back from the Voyager 1 in which the earth appears no larger than a pixel. He described our planet as a “pale blue dot,” the significance of which, if any, was dubious. Galileo opened the door to this line of thinking, and allowed us to begin seeing the universe as something bigger and more mysterious than just our corner of the neighborhood.
- Galileo avoided being burned at the stake (for claiming the Earth orbited the Sun) by recanting his scientific observations and spending the last nine years of his life under house arrest. Have we greatly advanced in our debating skills over the past 400 years, or is violence still too prevalent as a form of “dissenting opinion?”
- Humanity once thought the universe was only what could be seen in the night sky. Does the vastness of the universe we know today make you feel we are insignificant? Or does it fill you with wonder over what miracles and possibly what other life forms may be out there in that vastness?
- Do you welcome announcements of new scientific discoveries and get excited at the prospect of new discoveries always bringing a clearer picture of reality into focus? Or do you fear new science will ruin comfortable traditional ways of thinking?