That’s the day Galileo published the Sidereus Nuncius (Starry Messenger), starting one of the most important scientific revolutions in the history of humankind.
It’s a relatively small book, just about sixty pages long, and yet so very important! In it, Galileo put the descriptions and the hand-drawn pictures of everything he saw through the device that would become his legacy: the telescope.
Galileo didn’t actually invent the telescope (credit goes to unknown glass manufacturers in Holland); he wasn’t even the first person to point a telescope at the sky; but he definitely improved its performance and, most of all, he understood how important the telescope could be in making new astronomical discoveries.
Galileo first observed the Moon and discovered that it had valleys, mountains and craters, just like the Earth, proving that celestial bodies weren’t “perfect”, as was the common belief at the time. He also was able to see many stars that were invisible to the naked eye, demonstrating that the Universe was much bigger than assumed, maybe infinite. He discovered that the Milky Way was actually made of individual stars that could not be distinguished one from the other without the aid of the telescope. And he saw the most amazing thing of all: four new bodies, four satellites orbiting around the planet Jupiter. This was a clear proof that not everything in the Universe orbited around the Earth: could Copernicus actually be right in saying that the Earth moves around the Sun, and not vice versa?.
All these discoveries showed a very different view of the Universe from what people were used to, and Galileo wanted everyone to know about these new wonders. So he wrote the Sidereus Nuncius in a very simple style, so that it could be understood by all scholars (it was, after all, written in latin!) . He also added numerous drawings, which give a simpler and more direct message than written words (after all a picture is worth a thousand words), giving the reader the same experience that he himself had through his telescope.
