Today’s Factismal: Jupiter has 67 moons.
It isn’t often that someone invents one device that literally changes the way we see the Universe; what is exceptional about Galileo is that he invented two devices that did it. In 1625, he invented a occhiolino (“little eye”) that allowed him to explore the world of the miniscule; at a dinner in his honor, one of his students gave the device the name that we now know it by: the microscope (“seer of little things”). But that wasn’t his first foray into optics, nor his most famous. For that invention, we need to step back to 1609, when Galileo revealed his telescope (“seer of distant things”).
Though there were field glasses before Galileo, they had limited magnification and blurry images with rainbow rings due to by chromatic aberration caused by the poor quality glass that was available. Galileo got around these problems by using several lenses in series to adjust the image bit by bit. This method is still used today in binoculars and other optical devices.
Once Galileo had invented his telescope, he turned it onto the sky and saw nothing but trouble. One of the first things he saw was Jupiter and four bright points of light that circled around it. By the end of the week, he had proven that these small starry messengers revolved around Jupiter. Being a savvy sort, he published his findings in SidereusNuncius, a short treatise that was dedicated to Cosimo II de’ Medici and called the four moons of Jupiter “Medicean stars”. We now know them as Europa, Ganymede, Callisto, and Io and call them the Galilean satellites.
His invention literally changed the way we see the universe, but his discovery did so figuratively. Under Aristotle’s view of the cosmos, the Earth was the center and everything revolved around it. Things in the heavens were perfect and pure, and were in heaven because they were pure and perfect. Because the ideology fit so well with the dogma of the Catholic Church, it was adopted as Church Law – to challenge it was to challenge the very essence of belief. Though some troubling differences had arisen between the pure circles demanded by Aristotle and the observed paths of the planets, these were smoothed over by Ptolemy’s “epicycles” of circles on circles. Questioning these ideas was dangerous at best and heresy at worst.
Galileo did worse than question them: he made it possible for anyone to see that he was right and the Church was wrong. By simply looking through the telescope, people could see everything that he discovered. They could see the moons of another planet. They could see the “jug-ears” of Saturn. They could see the phases of Venus. They could see the spots on the face of the Sun and the scars on the face of the Moon.
Galileo was first rewarded for his discoveries and then punished for his hubris. He became a superstar in Pisa, and other city-states wooed him, trying to get him to move and to bring his beautiful ideas with him. But his ego led him to clash with others, making enemies out of supporters. Eventually, he was brought before the Inquisition for heresy and threatened with torture. He renounced his views and spent the rest of his life under house arrest. It would be 206 years before the Roman Catholic Church would take his works off of the banned list and 376 years before the Vatican would formally clear him of any wrongdoing.
In opening the heavens to us, Galileo laid the foundations of modern science. He showed that clear logic alone (Aristotle’s approach) is not enough. Logic must be backed with evidence and hypotheses must be checked against observations. If you would like to honor Galileo, there is no better way than in joining one of the citizen science groups that is classifying and naming features on the Moon!