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Galileo Galilei

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Galileo Galilei (1564-1642)

Galileo Galilei (born::February 15, 1564-Died::January 8, 1642) was an Italian mathematician, physicist, and astronomer. Sadly, he is most famous for his dispute with the Roman Catholic Church, after he challenged the prevailing cosmology, called geocentricity, of his day. In fact, his contributions to science include fundamental insights into the laws of motion and of gravity, in addition to his discoveries of the moons of Jupiter that collectively bear his name.[1]

Early life and career

Galileo Galilei was born in Pisa, Tuscany, in 1564, the first of either six or seven children. His father, Vincenzo Galilei, was a music scholar and wool merchant.[2][3][4][5]

In 1572 Vincenzo Galilei moved his wife and children back to his home town of Florence.[1][4] Vincenzo intended that young Galileo prepare for a career in medicine.[3] Galileo began his education in 1575 at a Jesuit monastery, but Vincenzo withdrew his son four years later after his son declared that he wanted to become a priest.[5] Two years after that, in 1581, Galileo enrolled at the University of Pisa to study medicine.[2] But Galileo took little interest in his studies, except for mathematics. In that field, according to legend, Galileo first observed a swinging lamp and timed its period. He was twenty years old at the time, and would not actually publish his insights into the Law of the Pendulum until eighteen years later.[2][5]

Galileo did not complete his studies,[4] and in fact gained a reputation while at college for frequent absenteeism and for expressing his opinions in a forthright and insolent manner.[5] The university threatened to fail him, but eventually allowed him to accept the personal tutelage of Ostilio Ricci, court mathematician of the Grand Duke of Tuscany.[4] In 1585, Galileo left college without completing his degree.[1][5]

Galileo began to earn his living by tutoring other students in math.[1][5] During this time he developed a small hydrostatic balance.[5] He applied for a position as mathematician at the University of Bologna, but was unsuccessful.[1][4] Then in 1589 he was appointed as chairman of the mathematics department at the University of Pisa.[1][4][5]

There he performed his famous experiment in which he dropped two balls of unequal weight from the top of an inclined plane[2] (not from the top of the Leaning Tower, as legend had it[5]) and observed that they both reached the bottom at the same time. Aristotle, considered the last word on physics at the time, had claimed that an object fell at a speed proportional to its weight. This and other direct challenges to Aristotle made Galileo unpopular enough.[1] His impatience with those who questioned his observations led him to describe his colleagues in vulgar terms while lecturing, a habit that irked the administration even more.[3][5] For those reasons, in 1592 the university terminated his contract.[1]

But in that same year he was appointed as mathematician at the University of Padua in the Venetian Republic.[2][3][4][5] He continued his experimental program, and built a rudimentary thermometer and a primitive pump. In 1596 he built a military compass for aiming cannons, and a civilian compass for use in surveying. Those inventions brought him the cash he desperately needed.[5] In 1602 he finally published his Law of the Pendulum, which states that the period of a pendulum is independent of the arc that it traverses. In 1609 Galileo determined that the motion of any falling body is a parabola, and that its horizontal motion is independent of its vertical motion.


Galileo did not marry. But he did have a relationship with a woman named Marina Gamba, who bore him two daughters (Virginia and Livia) and a son (Vincenzo). The two daughters each became nuns.[2][4]

The Astronomer

The first telescopic drawings of the Moon by Galileo Galilei
Also in 1609, Galileo received word of the exhibition of the first telescope in Venice. Galileo set about improving this instrument and in August of 1609 he had built an instrument that could achieve a magnification of eight or nine.[1][5] This instrument was useful primarily as a navigational aid for merchant ships and warships. But in December of 1609 he began to observe the sky with a twenty-power telescope.[1][2] In the winter of 1609-1610 he first observed the mountains of the moon, discovered that the Milky Way was in fact populated with stars, and then discovered four bodies orbiting Jupiter. He named these bodies the Sideri Medici; we know them today as the Galilean moons.[1][2][3][5][6] The Sideri Medici were important for another reason: because they were in orbit around Jupiter and not the Earth, their presence suggested (but did not quite prove) that the earth was not the center about which all things moved.[5]

He published his discoveries in a small volume titled Sidereus Nuncius (The Starry Messenger) in May 1610. One month later, he left the University of Padua and became court mathematician to the Grand Duke of Tuscany.[1][2][4][7] In that same year he made the first observations of Saturn (though he would not realize that Saturn had a broad ring around it), and of the phases of Venus. This discovery, together with his observations of the four largest moons of Jupiter, would eventually cause him to doubt the Aristotelian and Ptolemaic geocentricity system that the European church had adopted as dogma.[7]

In 1611 he traveled to Rome and was made a member of the Accademia dei Lincei.[4] In Rome he made his first observations of sunspots. In 1612 Galileo published his Discourse on Floating Bodies, a direct attack on Aristotle's theories of physics. In 1613 Galileo published his Istoria e dimostrazioni intorno alle macchie solari e loro accidenti (History and demonstration concerning sunspots and their properties), a work that offered a second challenge (his discovery of mountains on the Moon had been the first) to the notion that heavenly bodies were perfect.[1][4] The astronomer Christoph Scheiner attempted to argue that the sunspots were other bodies in orbit around the Sun, but Galileo showed convincingly that the sunspots were on or near the Sun's surface.[1][7]

The First Trial

Also in 1613, Galileo first challenged geocentricity in writing, and inquired into the reconciliation of the heliocentrism of Nicolaus Copernicus with certain passages of the Bible.[1][4] In 1614, Father Tommaso Caccini and other Florentine clerics stated publicly that Galileo should not be furthering Copernicanism.[1] Galileo went to Rome to defend his observations, but public and church opinion was against him. His most famous and detailed defense of his position is his Letter to the Grand Duchess Christina of Tuscany[4][8] In that letter, he wrote:

I do not feel obliged to believe that the same God who has endowed us with senses, reason and intellect has intended us to forego their use and by some other means to give us knowledge which we can attain by them. He would not require us to deny sense and reason in physical matters which are set before our eyes and minds by direct experience or necessary demonstrations.

He continued by reminding his patroness that the Bible was nearly silent on the planets and their motions, which was the key point of his dispute with the church. In this and other letters, Galileo essentially held that one ought to interpret the Bible non-literally if clear and convincing evidence existed that contradicted a literal interpretation. In all his writings, Galileo never challenged the truth of Scripture itself,[5] but said that human interpreters might be wrong about what Scripture actually said, and that they ought to revise their interpretation in light of direct physical evidence.

But at the time, the Roman Catholic Church reserved to itself the exclusive privilege of interpreting the Bible,[5] and so the Holy Inquisition held that the Copernican theory was heretical and contrary to Scripture. Galileo's continually caustic, arrogant, and disrespectful attitude toward any who disagreed with him did not help.[3] Cardinal Roberto Bellarmino, in 1616, admonished Galileo to refrain from advocating the Copernican theory.[1][2][4][5] A document of questionable authenticity was placed in the files of the Inquisition, stating that Galileo had been admonished officially.[1][7][9]

The Second Trial

Galileo did not become a stranger to controversy, then or ever in his life. In 1618, Galileo pointed out that three newly observed comets moved in such a path that they could not possibly be fixed in any rigid sphere around the earth.[1]

In 1623 Galileo's friend and admirer, Maffeo Barbarini, won election as Pope Urban VIII.[4] Galileo dedicated his work Il Saggiatore (The Assayer) in Pope Urban's honor.[1]

In 1624, Galileo invented the first microscope. Also at this time he traveled to Rome and had several discussions with Pope Urban. He argued from his theory of lunar tides (later shown to be erroneous[4]) that the earth could not be the fixed center of the universe. Pope Urban gave Galileo his verbal permission to write a book about theories of the universe but not to treat Copernican heliocentricity except as a hypothetical explanation.

Galileo began work on his Dialogo dei Massimi Sistemi (Dialogue on the Great World Systems). The "great systems" in the work were, of course, the systems of Ptolemy and Copernicus.[5] In 1630 Galileo went to Rome to seek permission to publish the Dialogue. He won permission in 1932 to publish it in Florence, but not in Rome.[1]

The publication caused the Church to ban it[5] and to summon Galileo for a second trial. At that trial, his prosecutors confronted him with the document mentioned above, one saying that Galileo had been given an official order that, presumably, he had willfully disobeyed.[9]. Galileo was convicted of heresy and forced to recant publicly his support for the Copernican system. (No historical warrant exists for Galileo whispering, Eppur si muove, or "It still moves," under his breath as he signed his confession.)[1] In 1633, he was allowed to go to his villa in Arcetri, where he continued under house arrest to the end of his life.[2][3][6][7]

Later life

In 1634 his daughter Virginia, then known as Sister Mary Celeste, died. In 1637 Galileo became totally blind. Some say that this was due to an infection of his eyes; others attribute his blindness to cataract disease and glaucoma.[6] Nevertheless, in 1638 Galileo published the Discorsi e dimostrazioni intorno a due nuove Scienze (Discourses and demonstrations on two new Sciences) in Leiden.[4] Galileo died in his villa on January 8, 1642.[5]


In 1822, the Church lifted its earlier ban on the Dialogo.[5] In 1992, Pope John Paul II formally declared that Galileo had done nothing wrong.[5][7]


Modern commentators credit Galileo with introducing to the practice of scientific investigation a rigorous method based on mathematics and logic.[4] These commentators also agree that Galileo was the first to challenge the notion that scientific investigation must begin with deference to prior authority, in this case the authority of Aristotle.[4] But Galileo did owe a debt to at least one prior investigator: Archimedes, from whom he got his ideas for his water balance and his pump, among other inventions.[4]

The image of Galileo as victim of a Church determined to suppress scientific knowledge in order to protect an erroneous faith is the favorite image of evolutionists today.[10] Gerard[3] points out, however, that no documentation remains that the Church ever actually condemned Copernicanism. Grigg points out the same thing that Galileo pointed out: that the Bible does not definitively declare that the sun moves around the earth. In this case, any verses that speak of a sun rising (Genesis 19:23 ) or setting (Genesis 28:4 ) are intended merely to fix a time of day and also properly describe apparent motion in the frame of reference of the earth.[10]

Grigg also states that geocentricity was largely a pagan idea, from men like Aristotle and Ptolemy. He then criticizes modern Christian leaders for dismissing the Bible too quickly on Galileo's account and also on account of the current prominent place of the theory of evolution in science education.[10]

Parnell[9] cites various actions by Pope John Paul II since soon after he assumed office, for the purpose of reconciling Church and science, and also criticizes secular scientists for discarding ethical and spiritual values and using Galileo's experience as an excuse.



[[Discovery::{{#ask:Discoverer::Galileo Galilei|link=none|limit=250|sep=| ]][[Discovery::}}| ]] {{#ask:Discoverer::Galileo Galilei |?Date of discovery |?Primary |?Semi-major axis |?Sidereal period |sort=Date of discovery,Primary,Semi-major axis |order=asc |format=table |mainlabel=Name |intro = List of celestial bodies discovered by Galileo Galilei: |}}


  • Law of Inertia, a discovery that Isaac Newton would build upon.
  • Law of the Pendulum
  • Law of Falling Bodies


  • 1586: La Balancitta (The Little Balance)
  • 1590: De Motu (On Motion)[4]
  • 1600: Le Mechaniche (Mechanics)[4]
  • 1610: Sidereus Nuncius (The Starry Messenger)
  • 1612: Discourse on Floating Bodies
  • 1613: Istoria e dimostrazioni intorno alle macchie solari e loro accidenti (History and demonstration concerning sunspots and their properties)
  • 1613: Letter to Benedetto Castelli on the relationship between science and the Bible.
  • 1615: Letter to the Grand Duchess Christina of Tuscany[8]
  • 1623: Il Saggiatore (The Assayer)
  • 1632: Dialogo dei Massimi Sistemi (Dialogue on the Great World Systems)
  • 1638: Discorsi e dimostrazioni intorno a due nuove Scienze (Discourses and demonstrations on two new Sciences)


  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 "Galileo." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. Accessed August 27, 2008.
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 Van Helden, Albert, and Burr, Elizabeth, eds. "The Galileo Project." Rice University, Houston, Texas, 1995. Accessed August 26, 2008.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Gerard, John. "Galileo Galilei." The Catholic Encyclopedia. Vol. 6. New York: Robert Appleton Company, 1909. Accessed August 26, 2008
  4. 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 Machamer, Peter. "Galileo Galilei." Stanford Encyclopedia of Philosophy, Stanford University, Stanford, California, March 4, 2005. Accessed August 27, 2008.
  5. 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 5.13 5.14 5.15 5.16 5.17 5.18 5.19 5.20 5.21 5.22 "Galileo Galilei." NASA, n.d. Accessed August 27, 2008.
  6. 6.0 6.1 6.2 Chew, Robin. "Galileo Galilei, Astronomer and Physicist." Lucidcafé, July 25, 2008. Accessed August 26, 2008.
  7. 7.0 7.1 7.2 7.3 7.4 7.5 "Galileo Galilei." High Altitude Observatory, University Corporation for Atmospheric Research, 2005. Accessed August 27, 2008.
  8. 8.0 8.1 Galilei, Galileo. "Letter to the Grand Duchess Christina of Tuscany." Reprinted in full by Paul Halsall in the Internet Modern History Sourcebook, Fordham University, August 1997. Accessed August 26, 2008.
  9. 9.0 9.1 9.2 Parnell, C. "Galileo Galilei." 2005. Accessed August 27, 2008.
  10. 10.0 10.1 10.2 Grigg, Russell. "The Galileo twist." Creation 19(4):30-32, September 1997. Accessed August 27, 2008.

External links