Intellectual Heritage

Galileo, The Starry Messenger, ed. Stillman Drake

STUDY GUIDE

This short essay changed the way we look at the world, winning instant (and initially positive) attention from the astronomers of the Roman College and other Church officials.

In this class, we will concentrate on Galileo's discoveries.   Please read from page 32 on with special care.  Please also consult the very useful short essay by Professor Dieter Forster of Temple's Department of Physics,  Galileo's  Starry  Messenger.

This publication inaugurated the series of events that culminated in  the epochal confrontation between Galileo and the Roman Catholic Church.  Although his discoveries were acknowleged, the way in which he presented them led to serious criticism, since he openly insisted that he'd found not just a better theory but better facts -- and these facts contradicted holy scripture, which placed the earth at the center of the universe.  (It was not only Catholics who were upset:  Martin Luther had condemned this sort of thinking in even stronger terms.)  Our task with this text is to focus on the particular discoveries that Galileo's method and his equipment (the telescope, which he had not "invented" but had constructed) made possible.  In many ways, Galileo was the first modern scientist: he insisted on acquiring detailed knowledge of the phenomena under consideration, and, to some degree,  he worked empirically, moving from the "facts" to a theory.    (Or, so it seems: there is dispute about this.)

Title page (21)

Note the date: March 1610 , Galileo's first major publication at age 46. Leads to his appointment as "Chief Mathematician and Philosopher" to the Medici court in Florence & his visit to Rome, spring 1611, where he was welcomed by the scientific academy, the pope, & the Jesuit Roman College, noted for its own famous astronomers. "When the head of the College, the Lord Cardinal Bellarmine, asked for their official opinion on the new discoveries, they unanimously confirmed them": i.e. the initial response of the Church is positive. (Koestler 4 -7, cf. Cohen 84) "The book became known throughout Europe immediately, and made a special impression in England."

Dedication (23-26)

Written in the tradition of ancient and renaissance prefaces. Nice illustration of attitudes to kingship, and of use of analogy so common in Shakespeare. "Just as these stars, like children worthy of their sire, never leave the side of Jupiter ..., so ...clemency, kindness..., gentleness..., splendor..., nobility... have all fixed their abode and habitation in Your Highness."

Galileo is addressing one of the Medici family, prominent or dominant in Florence, Italy, from the 14th century.  Machiavelli in The Prince also addresses a Medici ruler.  Both of these revolutionary thinkers sought governmental protection and support: only Galileo got it, winning a very well-paying professorship for the publication of this book.

Introductory comments (27-30)

How many achievements does G. catalogue here? What are they?

The Telescope (30-31)

You needn't master the details of this section.

Surface of moon (32-45)

This section is very important, because it reveals how much Galileo's telescope permitted him to see.  Copernicus in 1542 had suggested that the sun was the center of the solar system--as a theory, at least.  Kepler, Galileo's near-contemporary, had also come to this theory.  Galileo was the first to provide hard new data that the universe was not as everyone had thought.  Revealing that the moon had peaks and valleys was an important start.

Large vs. smaller spots. Attack on "philosophers": who are these? Spots signify mountains & valleys. Darker region = water. Large spots. Explanations of the smoothness of the moon's edges. Greater number of irregularities on lunar sutface than on earth's.

Estimated height of lunar mountains. "It is characteristic cf Galileo as a scientist of the modern school that as soon as he found any kind of phenomenon he wanted to measure it." (Cohen 73)

Cohen 74 remarks that Dante, writing in the 14th century, described the moon as an "eternal pearl . . . a perfect entity without blemish," the marks on which are not really there, despite the testimony of the senses and "reason." Be prepared to comment on the difference between Dante and Galileo as revealed by this passage.

Secondary light of moon (42-45): "earthshine" (Cohen 75-6); Gegenschein in German physics.  Can you explain this in your own words? Now, note that the planets, too, including the moon, "shine." What conclusions can you draw from this?

Fixed Stars (45-50)

Telescope fails to enlarge these much, since it reduces their radiance.

Stars differ in form from planets, which "look like little Moons" 154, see Toulmin 192f., Cohen 76-78). And more stars exist than we'd thought. Fainter stars likely mre distant, though there is as yet no noticeable parallax. (Toulmin 194). Discussion of Orion 155-156), etc.: many new stars.

Medicean stars 50-58

"The last of G's observations was the most exciting" (Toulmin 194-6): 4 largest satellites of Jupiter. "Most of [this] book is...devoted to...methodological observations of Jupiter and the 'stars' near it." (Cohen 79) Is "stars" the correct word to use?  How did this discovery affect people's understandinq of the heavens?

Cohen 80 remarks that "Galileo,...could not explain why ... Jupiter could move in its orbit without losing its four encircling companions, any more than...how the earth could move through space and not lose its one encircling moon."  It is worthwhile to ask why Galileo would have trouble with these questions.

Cohen, 83 summarizes three other discoveries made by Galileo with his telescope that don't appear in Starry Messenger: 1) the phases of Venus (proof that Venus shines only by reflected light), and Venus' orbit around the sun & varying distance from earth; 2) rings or "ears" of Saturn; 3) sunspots, which show that sun is not perfect, and that it rotates at a known speed.

Words worth knowing: parallax

References:

Koestler = Arthur Koestler, The Sleepwalkers (N.Y.: MacMillan, 1959); Cohen = I. Bernard Cohen, The Birth of a New Physics (Garden City, N.Y.: Doubleday, 1960); Butterfield = Herbert Butterfield, The Origins of Modern Science 1300-1800, rev. ed. N.Y.: The Free Press, 1957); Drake = Stillman Drake, Galileo at Work. A Scientific Biography (Chicago: Chicago UP, 1978); Morphet = Clive Morphet, Galileo and Copernican Astronomy: A Scientific World View Defined (London: Butterworths, 1977); Kuhn = Thomas S. Kuhn, The Copernican Revolution (Cambridge: Harvard UP, 1957); Toulmin= Stephen Toulmin and June Goodfield, The Fabric of the Heavens (N.Y.: Harper, 1961)

Useful web pages:

http://csep10.phys.utk.edu/astr161/lect/history/galileo.html