Chapter 3.3 Notes continued

How did Galileo solidify the Copernican revolution

·         Galileo (1564-1642) overcame major objections to the Copernican view. Three key objectives rooted in the Aristotelian:

Earth could not be moving because objects in air would be left behind.

Noncircular orbits are not perfect as heavens should be.

If earth were really orbiting sun, we’d detect stellar parallax.

Overcoming the first objection

·         Galileos experiments showed that objects in air would stay with a moving earth.

Aristotle thought that all objects naturally come to rest.

Galileo showed that objects will stay in motion unless a force acts to slow them down (Newtons first law of motion)

Overcoming the second objection

·         Tychos observations of comet and supernova already challenged this idea.

·         Using his telescope, Galileo saw:

Sunspots on the sun.

Mountains and valleys on the moon (proving it is not a perfect sphere).

Overcoming the third objection

·         Tycho thought he had measured stellar distances, so lack of parallax seemed to rule

out an orbiting earth.

·         Galileo showed stars must be much farther than tycho thought—in part by using his telescope to see that the Milky Way is countless individual stars.

·         I stars were much farther away, and then lack of detectable parallax was no longer so troubling.

·         Galileo also saw four moons orbiting Jupiter, proving that not all objects orbit earth.

·         Galileo’s observations of phases of Venus proved that it orbits the sun and not earth.

·         In 1633 the Catholic Church ordered Galileo to recant his claim that earth orbits the sun.

·         His book on the subject was removed from the church’s index of banned books in 1824.

·         Galileo was formally vindicated by the church in 1992.