Case Study:  HOW COSMOLOGY BECAME A SCIENCE  

The Book of the Cosmos. Imagining the Universe from Heraclitus to Hawking. 

Ch. 24. Neither Known Nor Observed by Anyone Before, Galileo Galilei. “An ambitious professor inaugurates the age of the telescope by telling how he discovered the true face of the moon, the moons of Jupiter, and the secrets of the Milky Way.”

First passage:

•          Why was Galileo so excited about the newly invented telescope?

•     Why does it matter, how many stars there are in the sky?

•          Why does it matter, that the surface of the moon is not smooth but rough, “just like the surface of the earth itself?”

•          Why does it matter, the nature of the Milky Way, or of “nebulous” stars?

Second passage:

•          Why does Galileo describe how he constructed his telescopes?

•          Put yourself in the place of a common man in Galileo’s time. What might be some of the “great advantages” the telescope would provide? Why did Galileo, instead, turn his telescope to the heavens?

•          Galileo describes the moon’s dark and bright areas as they appear under the changing illumination of the sun. He interprets the observations by analogy with the effect of the sun on valleys and mountains on the earth. If the moon is in the heavens, why is this a legitimate analysis?

Third passage:

•          Why does Galileo describe in detail the explanation of the moon’s phases, as seen from the earth?

•          Why was it a novel concept, that the moon is itself illuminated by the earth? What does this suggest about the relationship of the earth and the moon? The earth and the heavens?

Fourth passage:

•          Why is it important to classify stars in terms of stellar magnitude? How has the interpretation of this measure changed from ancient to modern times?

•          The apparent sizes of stars are not magnified as much by the telescope, as the apparent sizes of the moon and nearby objects are magnified. Why does this necessitate an explanation from Galileo?

•          In ancient times, all stars were assumed to be the same distance from the earth. What indicates to Galileo that this is may not be so?

•          What is the modern term for “nebulous” stars? Was Galileo correct in his understanding of these?

Fifth passage:

•          How did Galileo know that the small stars he saw near Jupiter were not ordinary stars?

•          Why did Galileo describe his observations of the four moons of Jupiter in such detail? Why did he name them “the Medicean stars?”

•      What is the fundamental significance of the discovery by Galileo of the moons of Jupiter?

Sixth passage:

•          Why did people find it so impossible, to imagine that two objects might revolve around each other, and at the same time orbit the sun? How does Galileo fix this problem?

•          In what sense was Newton’s work “prepared and defined by Galileo?”

The article as a whole:

•          Some people in Galileo’s time, in particular the Pope, found his work threatening to their worldview. Why? Was Galileo a religious man? Did his work contradict sacred scripture?

•          Consider the kinds of arguments Galileo uses to interpret his observations of the moon and other heavenly bodies. How did he view the relationship between the earth and the heavens?

•          Galileo was very excited about his discoveries, but these were eventually the source of a great deal of trouble for him. He was eventually forced to recant his support for the Copernican heliocentric theory, and ended his life under house arrest, forbidden to teach that the earth revolves around the sun. Do you think he was surprised by this? Should he have been? Can you think of something analogous that might happen today?