1. Galileo Galilei
for 5/31 – 6/1/16
Read the secondary handout and textbook primary source on p. R56 to complete this bell.
Primary Source
The Starry Messenger
Secondary Source
A. His telescopes
A. Findings from Telescope Use
1. How did Galileo construct his first telescope?
1. What could Galileo conclude after his observations of Jupiter’s moons?
2. What was the first telescope able to do?
2. What was Galileo able to propose for testing (hypothesis) after observing the phases of the planet Venus?
3. What was the second telescope able to do?
3. Ultimately, what could Galileo conclude from all of his telescope observations?
4. What was his third telescope able to do?

2. DISCOVERIES FROM GALILEO’S TELESCOPES
Galileo did not invent the telescope, but he was the first to make powerful telescopes with good optics. He was also among the first to train his telescopes on the sky.
What Galileo saw through his telescope eventually helped show that Earth was not the center of the universe. Galileo’s observations were strong evidence for the Copernican theory that Earth and other planets revolve around the sun. Galileo was first to observe four moons orbiting the planet Jupiter. He saw these as tiny stars near the equator of the planet, changing position from night to night. If these bodies revolved around Jupiter and not Earth, didn’t it stand to reason that other bodies might not be revolving around Earth either? Galileo also observed the planet Venus and noticed that it had phases similar to the phases of the moon. However, Venus appeared equally bright no matter what its phase. Galileo hypothesized that Venus could not be making a circular orbit around Earth for this to be true; it had to be much farther away in its full phase and much closer in its crescent phase. This supported the idea that Venus revolved around the sun rather than Earth.