407 years ago tonight, on January 7, 1610, the Pisan astronomer Galileo Galilei looked up at a brilliantly-shining Jupiter through his own handmade telescope and saw three bright little “stars” next to it, stirring his natural scientific curiosity. Further observations over the next several nights showed that the planet wasn’t moving relative to the little “stars” as it should if they were distant background stars, but rather the bright objects (of which he soon saw four) were moving along with Jupiter. Galileo correctly concluded that those little objects weren’t stars at all but rather moons that orbited the distant planet—and, most importantly, not the Earth. This cosmic revelation forced a change of the entire view of our solar system (causing no end of trouble for Galileo as the Church didn’t appreciate a challenge to their Earth-centered Universe) but also opened the door for the discovery of many more moons around other planets.
Jupiter is now known to have at least 50 moons, with possibly as many as 67.
As a result of his research and publications regarding the observed motions of bodies in the solar system Galileo was eventually sentenced as a heretic by the Inquisition in Rome and spent the last nine years of his life under house arrest. Still, his legacy of observation and science over dogma and established belief lives on to this day… and if you go outside on a clear morning before sunrise you can see a brightly-shining Jupiter in the southeast near Spica, just as Galileo did 407 years ago. Take even a small telescope or pair of binoculars and you will easily see its four largest moons—Ganymede, Callisto, Io, and Europa—as pinpoints of light beside it. Thanks to Galileo and others like him, we now know what those are, and that there are countless other worlds and moons out there like them just waiting for our discovery.
*Eppur (or e pur) si muove – “and yet it moves” is a quote often attributed to Galileo in that he muttered it as he “recanted” and accepted his punishment from the Roman court. But it is likely apocryphal, as there is no mention of it in contemporary court records from the time.