What were Galileos most important astronomical discoveries?
Galileo began his astronomical observations in late 1609. He rushed the earlier ones into print by March 1610 in a little book written in Latin entitled Sidereus nuncius (i.e. Starry Messenger). His most important observations published there were: a) The Moon has a rugged landscape containing mountains and valleys that look very much like landscape features on Earth. This contradicted the Aristotelian notion that all bodies beyond Earth are made of a perfect celestial substance: The Moon looked like it was made of the same stuff as Earth. b) The light of the Milky Way comes from the combined light of countless stars too dim to see with the human eye, but revealed by the telescope. Other parts of the sky also contain previously unknown stars and nebulous objects that are revealed by the telescope. c) Jupiter is orbited by four moons (Galileo called them planets), previously unknown, which show that Earth is not the sole center of motion in the cosmos (as was maintained by the Aristotel
