What did Galileo discover with his telescope?
• The craters and “seas” of the Moon. • The fact Venus changed shapes–crescent, etc.–like the Moon, confirming it was a sphere illuminated by sunlight. • Four large Moons of Jupiter, forming a small “solar system” around that planet. This confirmed to Galileo the ideas of Copernicus. • Sunspots, though others also observed them at about the same time. • He discovered the rings of Saturn. However, Galileo’s telescope was so crude that he was not sure what they were. • The Milky Way, a whitish cloud stretching across the heaven: Galileo found it was composed of many faint stars. We now know that the Earth is part of the galaxy, a collection of at least 100 billion stars, forming a flat wheel-shaped cloud. When we look at the Milky Way, we are seeing that cloud edge-on and therefore observe many distant stars. [Optional discussion: Should one say “the galaxy” or “a galaxy”? Actually, “the galaxy” was the term used for many centuries for this collection of stars–it means the milky way,
