Sidereus Nuncius

"This is a thrilling book. It is the moment that astronomy became an observational science. Until Galileo’s time, the most that anyone could know about a planet was where it was. With his telescope Galileo was able to determine the composition of the moon. He was also able to solve various longstanding mysteries, such as what is the Milky Way – by looking through the telescope he could see that it was made up of myriad stars. Perhaps his most exciting discovery was finding the moons of Jupiter. Because of that he could say to the world: “Earth is not the only centre of revolution; there are these bodies going around Jupiter.” “Every child knows that the earth revolves around the sun. But if you had to figure it out for yourself it would be extremely difficult. There aren’t a lot of clues.” In Galileo’s time another objection to the earth’s motion was, what about the moon? How could the earth travel around the sun and carry the moon along with it? Well here was Jupiter with four moons and so, obviously, having moons was no impediment to orbiting the sun. Whether you thought Jupiter orbited the earth or orbited the sun it was moving along with all those moons. And so he removed an obstacle to accepting the idea. He had heard of such a thing being invented as a novelty and so he figured out how to build one. And although at first he considered it a military tool, which was passed to the navy in Italy to keep watch on the horizon for enemy ships, he very soon realised he could turn it skywards. So he made these amazing discoveries and published them. A brilliant, inventive, religious and excited individual who was open to new things. He was an outsized character."