Starry Messenger (1610)

1. What were Galileo’s telescopic observations?

3. How did he use them to attack & undermine Aristotelianism?

2. Did these observations prove the Copernican system?

4. Were his troubles with the Church simply “science” versus “religion”?

SIDEREAL MESSENGERunfolding great and very wonderful sights

and displaying to the gaze of everyone,but especially philosophers and

astronomers,the things that were observed by

GALILEO GALILEIFlorentine patrician and public mathematician

of the University of Padua,with the help of a spyglass lately devised by him,

about the face of the Moon, countless fixed stars, but especially about four planets

flying around the star of Jupiter at unequal intervals

and periods with wonderful swiftness;which, unknown by anyone until this day,

the first author detected recently and decided to name

MEDICEAN STARS

Most Serene Cosimo, [when] I discovered these stars . . . I decided by the highest right to adorn them with the very august name of Your family. . . For to be silent about Your Most Serene Highness’s ancestors to whose eternal glory the monuments of all histories testify, Your virtue alone, Great Hero, can, by Your name, impart immortality to these stars . . .Most Merciful Prince, acknowledge this particular glory reserved for You by the stars and enjoy. . . divine blessings carried down to You. . . from the Maker and Ruler of Stars, God.

“[The moon] is not robed in a smooth and polished surface . . . [but is] rough and uneven, covered

everywhere, just like the earth’s surface, with huge prominences, deep valleys, and chasms.”

“You will behold through the telescope a host of other stars, which escape the unassisted sight, so numerous as to be beyond belief.”

“I have observed the nature and the material of the Milky Way . . . Upon whatever part of it the telescope is directed, a vast crowd of stars is immediately presented to view. Many of them are rather large and quite bright, while the number of smaller ones is quite beyond calculation.”

“[Now] we have not just one planet rotating about another

while both run through a great orbit around the sun; our own eyes show us four stars which

wander around Jupiter as does the moon around the earth, while altogether trace out a grand

revolution about the sun in the space of twelve years.”

Frontispiece:Dialogue on the Two Chief World Systems (1632)

Characters:SalviatiSagredoSimplicio

I say that it seems prudent that Your Paternity and Mr. Galileo are proceeding prudently by limiting yourselves to speaking suppositionally and not absolutely, as I have always believed that Copernicus spoke. For there is no danger in saying that, by assuming the earth moves and the sun stands still, one saves all the appearances better than by postulating eccentrics and epicycles; and that is sufficient for the mathematician. However, it is different to want to affirm that in reality the sun is at the center of the world. . . and the earth. . . revolves with great speed around the sun; this is a very dangerous thing, likely not only to irritate all scholastic philosophers and theologians, but also to harm the Holy Faith by rendering Holy Scripture false. . .

Cardinal Bellarmine, Letter to Father Foscarini, 1615

[In] order that this opinion may not creep any further to the prejudice of Catholic truth, the Congregation has decided that the books by Nicolaus Copernicus and Diego de Zuñiga be suspended until corrected; and that all other books which teach the same be likewise prohibited. . .

Decree of the Index of Prohibited Books, 1616I would be greatly inclined to agree that the cause of tides could reside in some motion of the basins containing seawater; thus, attributing some motion to the terrestrial globe, the movements of the sea might originate from it. . .

Galileo, Discourse on the Tides, 1616

Salviati: . . . I say that human wisdom understands some propositions as perfectly and is as absolutely certain thereof, as Nature herself; and such are the pure mathematical sciences, to wit, Geometry and Arithmetic. In these Divine Wisdom knows infinitely more propositions, because it knows them all; but I believe that the knowledge of those few comprehended by human understanding equals the Divine, as to objective certainty . . .

Simplicio: This seems to me a very bold and rash expression.

First Day, Dialogue

Simplicio: But in case we should give up Aristotle, who is to be our guide in philosophy? Name you some author.

Salviati: We need a guide in unknown and uncouth parts, but in clear thoroughfares, and in open plains, only the blind stand in need of a leader . . . But he who has eyes in his head and in his mind has to use these for his guide. Yet mistake me not. . . I commend the reading and diligent study of [Aristotle] and only blame the servilely giving one’s self up a slave to him, so as blindly to subscribe to whatever he delivers. . .

Second Day, Dialogue

[Many] times in the work there is a lack of and deviation from hypothesis, either by asserting absolutely the earth's motion and the sun's immobility, or by characterizing the supporting arguments as demonstrative and necessary, or by treating the negative side as impossible . . .

. . .[Galileo] wrongly asserts and declares a certain equality between the human and the divine intellect in the understanding of geometrical matters . . .

Report on the Dialogue, 1632Although at the beginning of his book Galileo claims to want to deal with the earth's motion as a hypothesis, in the course of his Dialogue he puts the hypothesis aside and proves its motion absolutely, using unconditional arguments . . .

Report on the Dialogue, 1633

I must altogether abandon the false opinion that the Sun is the center of the world and immovable and that the Earth is not the center of the world and moves and that I must not hold, defend, or teach in any way whatsoever, verbally or in writing, the said false doctrine, and after it had been notified to me that the said doctrine was contrary to Holy Scripture- I wrote and printed a book [Dialogue] in which I discuss this new doctrine already condemned and adduce arguments of great cogency in its favor without presenting any solution of these, I have been pronounced by the Holy Office to be vehemently suspected of heresy. . . I, Galileo Galilei, have abjured as above with my own hand.

Galileo’s recantation, 1633