Friday, March 23, 2012

Galileo Galilei (1564-1642): The Starry Messenger

by G. Jack Urso

While Nicolaus Copernicus, Tycho Brahe, and Johannes Kepler avoided major confrontations with the church, Galileo Galilei found himself in a serious struggle with the Vatican as a result of his research. By 1609, when Galileo published his first work based upon his observations with the telescope, Europe had enjoyed nearly 100 years of Protestantism. Perhaps enjoy isn't quite the right word for it for in reaction to Protestantism came the Inquisition. It is with that force that Galileo, unlike his predecessors, had to contend. 

Early Years

Fig. 1: Galileo Galilei
circa 1636.
Born in 1564 in Pisa, Italy, Galileo's father was a musician and his mother quite educated for a woman of her time and class. Galileo's father, in addition to a talent for math, was mistrustful of authority; characteristics he passed on to his son. Galileo received his early education from local monks; however, when his father learned that his son was considering joining the local monastery he immediately withdrew Galileo and sent him off to the University of Pisa School of Medicine. Here, Galileo conducted experiments with a pendulum that helped him form ideas that eventually led to his law of falling bodies (McMullin 52-53).

In the early years of his career in Pisa, Galileo lectured and wrote on mathematics and mechanics while criticizing Aristotle's science. Galileo also imprudently criticized an engineering proposal by one of the members of the Medici ruling family, which led to his departure to Padua in 1592. There, Galileo served as chair of the mathematics department at the University of Padua until 1610 and it was here that he became acquainted with an instrument that would literally open the eyes of astronomers everywhere, the telescope (McMullin 54-55).

Galileo had long been aware of the inaccuracies of Aristotelian science. For example, he could not help noticing that large and small hailstones hit the ground at the same time, contradicting Aristotle's teaching that heavy objects fall faster than light objects (McMullin 54). Galileo's famous "experiment" from the top of the Leaning Tower of Pisa (circa 1590) did not take place as reported. He instead demonstrated his point by rolling balls down an incline. Similar experiments though had been previously documented. Benedetti Giambattista published his results in 1553, followed by Flemish engineer Simon Stevin who published his findings in 1586 (Hawking 16, 55). Galileo may have been challenged by the conservative academic climate of Pisa to conduct his own experiments.

The Starry Messenger

Fig. 2: Galileo's telescope
In 1604, a nova appeared that gave Galileo an opportunity to show that Aristotle was wrong, yet again, in suggesting the heavens are unchanging (a belief endorsed by the Catholic Church). Tycho Brahe's studies of the nova of 1574 gave credence to what Galileo theorized, so, in 1609, Galileo constructed his first telescope which allowed him to support his propositions with evidence. The original Dutch patent for the telescope indicates that it was intended for land observation, not the night sky. Hearing about the device from a clergyman friend, Galileo made one of his own with the ability to magnify a distant object nine times, far exceeding the original Dutch design. The following year, in 1610, Galileo published Sidereus Nuncius (The Starry Messenger), which detailed his observations of the mountains of the Moon, four moons of Jupiter, and "innumerable" stars unseen by the naked eye (Hawking 57-58). All first seen and documented by Galileo.
Fig. 3: On left - Drawing of the Moon by Galileo
On right - Photograph of the Moon from the same angle
Kepler read Sidereus Nuncius and endorsed its findings before ever seeing a telescope. That he accepted Galileo's observations, even though he lacked the instrumentation to duplicate the results, is a testament to the influence of Sidereus Nuncius. Kepler wrote a long letter to Galileo discussing his impressions and even wrote the Duke of Tuscany, Giuliano de' Medici, to praise his most noted resident's work (Kepler 3, 9). This letter was published in Prague in 1610 and lent crucial support to Galileo's findings in the secular world. Predictably, the Catholic Church had a different opinion on the matter.

On Floating Bodies and Sunspots

In 1612, Galileo was once again on the attack against Aristotelian science. His Discourses on Floating Bodies discussed what causes an object to float as well as the physical nature of ice. In the book Galileo also provides a number of simple experiments that contradict the Aristotelian position on the nature of buoyancy. Galileo would defend this work against numerous academic attacks (McMullin 59-60).

Also in 1612, a German Jesuit priest published observations of sunspots and explained them as small planets orbiting the sun. Although this is in keeping with the church's view that the sun was perfect and therefore free of such imperfections as a blemish on its surface, the Jesuit was nonetheless compelled to publish under a pseudonym in order to protect himself from prosecution. Galileo, who had observed sunspots sometime prior to 1612, published his own conclusions in a series of letters in 1613. Not only did Galileo correctly assert that sunspots were an ever-changing manifestation of the Sun itself, but he also signed his name, giving those who opposed any challenge to the Church a target. In 1614, he was denounced from the pulpit in Florence and the Inquisition soon took up the matter on referral from a Dominican priest (McMullin 59-60).


In 1615 the Church begins its counterattack against the Copernican Revolution. Pope Paul V declared the Sun and Earth did not move and Galileo was ordered to cease espousing views to the contrary (Ollney 89). Additionally, the pope effectively banned Copernicus' De Revolutionibus by suspending it “pending correction.” Galileo, in Rome to answer his accusers, defended his views only to be commanded by the pope to remain silent. Recalled to Florence, Galileo entered a period of scientific inactivity for the next two years (McMullin 61).

The Dialogue

It was not until Pope Urban VIII succeeded Pope Paul V in 1624 that was Galileo able to resume public discourse of his ideas on cosmology. The new pope gave Galileo permission to discuss his ideas in a hypothetical context. The result was Dialogue on the Two Great World Systems (1632) (Dialogue on the Two xviii). Rather than a text of observations, calculations, diagrams and maps, Galileo presents the discussion of the difference between the two competing world systems as a discourse between three "interlocutors," Salviatus, Sagredus and Simplicius (Dialogue Concerning 6).

Salviatus is a proponent of the Copernican system. Sagredus and Simplicius argue for the Aristotelian view. Over the course of four days various issues with both systems are discussed. Salviatus is imbued with Galileo's persuasive prowess. Sagredus has a mind open to civilized conjecture while Simplicius, on the other hand, is obnoxious and rude (Dialogue Concerning 7). Although the book ends with affirmations of the glory of God, it led to a serious encounter with the Inquisition. Naming the defender of the Aristotelian world-view "Simple" probably didn't earn Galileo any favor with the inquisitors.

Later Years

In 1633, almost seventy, Galileo went to Rome to stand trial. The case centered around the injunction originally filed against Galileo in 1616 after his last trial. The inquisitors had an unsigned memorandum from the Church's records suggesting that Galileo did indeed exceed the injunction's commands. Galileo, however, produced a signed letter from the original trial that his prosecutors did not know existed. This letter, from the Cardinal in charge of the 1616 trial, left room for doubt regarding Galileo's guilt (McMullin 63).

Sentenced to life in prison and prohibited from writing about Copernicanism, Galileo was allowed to return to his home near Florence under the close scrutiny of the Inquisition. All of Galileo's works, published and unpublished, were banned. To their credit, it should be noted that three of the ten cardinal-judges conducting the trial refused to sign the decree of sentence (Langford 153).

The Two New Sciences

Despite the ban on the publication of his works Dialogue Concerning the Two Chief World Systems was published in Strasbourg in 1635 out of reach of the Vatican's control (Langford 157). Galileo did not cease writing in the face of the Inquisition. Using the same characters from Dialogue Concerning the Two Chief World Systems, Galileo finished work on The Two New Sciences in 1636. In it, he establishes laws of accelerated motion and of falling bodies as well as basic theorems regarding projectile motion - ballistics (McMullin 64).

Similar in format to the Dialogue of 1632, it also uses the same interlocutors Salviatus, Sagredus, and Simplicius. Galileo presents his theory regarding ballistics, which deals with resistance, cohesion, and acceleration in bodies in motion as well as proof of parabolic trajectories in projectiles. This theory was in opposition to Aristotelian science which taught that projectiles went straight out, then straight down (Dibner and Drake 37).

Galileo's sight continues to fail until he finally goes blind in 1637, just after finishing The Two New Sciences. The following year, in 1638, The Two New Sciences is published in Leyden, Holland. Galileo got around the ban on publication by reporting that the book was published without his permission. He spent his final years dictating new chapters for The Two New Sciences and occasionally teaching and lecturing until passing away in 1642, the same year Isaac Newton was born (Langford 158).

The Catholic Church, by the way, never got around to officially forgiving Galileo until 1981 (Ross 21).

Related Content

 Works Cited
Dibner, Bern and Stillman Drake. A Letter from Galileo. Norwalk:
              Burndy Library, 1967. Print. 

Galilei, Galileo. Dialogue Concerning the Two Chief World 
              Systems-Ptolemaic and Copernican. Trans. Stillman Drake.
              Berkeley and Los Angeles: University of California Press,
              1967. Print.

---. Dialogue on the Two Great World Systems. Ed. Giorgio de
              Santillana. Chicago, Toronto and London: The University
              of Chicago, 1955. Print.

Hawking, Stephen W. A Brief History of Time. New York, Toronto
              and London: Bantam Books, 1988. Print.

Kepler, Johannes. Kepler's Conversation with Galileo's Sideral
              Messenger. Trans. Edward Rosen. New York and London:
              Johnson Reprint Corporation, 1965. Print.

Langford, Jerome, J. Galileo, Science and the Church. New York:
              Desclee Company, 1966. Print.

McMullin, Ernan, ed. Galileo: Man of Science. New York and
              London: Basic Books, Inc., 1967. Print.

Ollney, Allan. The Private Life of Galileo. London: MacMillian &
              Co., 1870. Print.

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