Galileo: the first* astronomer to use a

telescopeBob Joseph

Institute for Astronomy

University of Hawaii

Early career:Pisa & Padua

Early life

• Born in Pisa in 1564 to an old & distinguished Florentine family.

• Matriculated at Univ of Pisa in 1581 to study medicine.

• Heard lecture on Euclid, began studying mathematics on his own, and left the Uni without a degree in 1585.

• Went home to Florence, did some teaching, and gave several well-received public lectures on mathematics.

• Appointed to Chair of Mathematics at Pisa in 1589.

• In 1592 he successfully competed for the Chair of Mathematics at the Univ of Padua (Republic of Venice).

• Remained at Padua for the next 18 years.

Padua

• Galileo produced three children with his common-law wife, a Venetian woman named Marina Gamba.

• At Padua Galileo did much of the experimental work on projectiles and falling bodies which later enabled him to lay the groundwork for the theory of mechanics.

• He also developed the “geometric and military compass,” which spread his fame and brought additional income.

The Astronomical Context

Astronomical context

• The geo-centric cosmology of Plato & Aristotle, refined by Claudius Ptolemy ca. 2nd C CE, remained the model of the heavens for 1,500 years.

• It was the common-sense model of the heavens in Galileo’s time.

• It was also quite accurate.

The Medieval Cosmos

• The Scholastic philosophers, especially St. Thomas Aquinas, had integrated Aristotle’s philosophy and logic with Christian theology.

• This had been adopted as official doctrine by the Catholic church.

• This included the Ptolemaic geo-centric cosmology.

Copernicus’ helio-centric system

• In 1543 Copernicus had proposed a helio-centric cosmology.

• His aim was to simplify Ptolemy’s model and to get back to Aristotle’s fundamental dynamical principles.

• His model was a bit simpler, but no more accurate, and violated the common sense of Aristotle’s physics.

Telescopic discoveries

Galileo ca. 1610-1615

The Telescope

• In July 1609 Galileo heard from a friend in Venice about an optical instrument which magnified distant objects.

• Galileo immediately worked out the optical theory and taught himself how to grind lenses.

• His first telescope magnified 3x, but by August 1609 he went to Venice with an 8-power telescope.

• He demonstrated its performance to the Venetian Senate, and gave it to the city.

• This would be a magnificent boon to the powerful Venetian navy.

• In return he was given a lifetime appointment at the University and his salary was doubled.

Telescope deficiencies

• These simple telescopes, with spherical optics, suffered from both spherical aberration and chromatic aberration: therefore no sharp focus.

Galileo’s telescope

• Galileo realized that stopping down with an aperture smaller than the size of the lenses improved the image quality substantially.

• The telescopes also had a very small field of view: ~15 arcmin (1/2 of diameter of the Moon).

• This made it difficult to find objects.

First telescopic discoveries

• By December of 1609 or early 1610 Galileo had used his telescopes to discover:

! The Moon has a cratered surface with mountains and valleys--like those on Earth.

! Diffuse patches of light in the heavens (“nebulosities”) were resolved into hundreds of discrete stars, and many more stars were found in well-known constellations.

! Jupiter has four satellites orbiting round it--now known as the “Galilean Satellites.”

The Sidereus Nuncius

• Galileo was acutely aware that the telescope was a simple instrument, easily duplicated, and he could be scooped.

• On 12th March 1610 Galileo published a 40-page booklet called the Sidereus Nuncius (Starry Messenger), describing these discoveries.

• It became widely-read and celebrated.

Galileo’s astronomical discoveries

• In contrast to others who had access to telescopes, Galileo was the first* person to point it at celestial objects.

• One of his first discoveries was mountains and craters on the Moon.

The Pleiades

• Galileo found 36 stars in the Pleiades constellation.

• He also resolved other nebulosities know since ancient times into clusters of individual stars.

• When observing the faint band of light, the Milky Way, he found it was composed of “numberless stars.”

Inner moons of Jupiter

• Galileo realized the 4 “stars” close to Jupiter were in fact orbiting around it, and he measured their periods quite accurately.

• These are known today as the “Galilean moons.”

Move to the Medicean Court

Return to Florence

• Galileo had always hoped to return to Florence.

• He realized that his reputation and fame from his telescopic discoveries might get him a position in the Medicean Court in Florence.

• He asked the Court for permission to name the new “stars” orbiting round Jupiter the “Medicean Stars,” and to dedicate the book to Cosimo II, the new Grand Duke.

Move back to Florence

• This request was awkward for the Medicis, but they eventually agreed.

• Galileo followed this up with a request for an appointment to the Medici Court.

• He was granted this position with the title First Philosopher and Mathematician to the Grand Duke.

• Galileo moved from Padua back to Florence in September 1610.

• He never returned to Padua, although he said later the years at Padua were the happiest years of his life.

Publicizing the discoveries

• Galileo was a great self-promoter.

• He used his connections with the powerful Medici family to publicize his scientific discoveries.

• He sent copies of his book to the Tuscan ambassadors in other countries.

• He also sent telescopes to important and powerful people throughout Europe.

• However, he never gave a telescope to anyone who was knowledgeable and might scoop him in future discoveries--e.g. Kepler.

Further telescopic discoveries

Saturn’s “handles”

• Galileo’s telescopes did not have sufficient resolving power to distinguish the rings of Saturn.

• However he did see that Saturn is sometimes not round, but either “olive-shaped,” or has “handles.”

Ptolemaic vs. Copernican phases of Venus

Only crescent phases. Full range of phases.

Discovery of sunspots

• Ca. 1612 Galileo discovered sunspots.

• He tracked them throughout solar rotations and argued they are on or close to the Sun.

• He also got into a long dispute about discovery priority with the Jesuit Father Christopher Scheiner.

Conflict with the Roman Inquisition

First trip to Rome

• In 1611 Galileo made a trip to Rome.

• He received an enormous welcome by both academics and Church leaders.

• The Jesuit Collegio Romano gave him a big banquet.

• The senior astronomers at the College informed the Chief Theologian at the Vatican, a Jesuit named Roberto Bellarmino, that they had confirmed Galileo’s telescopic discoveries.

• It was a hugely successful experience for Galileo.

Anti-Galileo reaction

• Meanwhile, an anti-Galileo faction, chiefly of a few university professors and Dominicans, had been developing.

• One or two members of this group denounced Galileo to the Inquisition.

• Nothing came of this.

• However, the Holy Office did engage 11 consultants to report on two assigned questions:

! The Sun is the center of the world and hence immovable of local motion.

! The Earth is not the center of the world, or immovable, but moves according to the whole of itself, also with a diurnal motion.

Letter to the Grand Duchess

• On page 2 of the Sidereus Nuncius Galileo makes his first published statement that he accepts the sun-centered cosmology of Copernicus.

• In 1615 Galileo wrote a widely-circulated Letter to the Grand Duchess Christina, in which he presented his view on the relation between science & religion.

• He comments: “The Scriptures instruct us on how to go to heaven, not how the heavens go.”

• Galileo rather arrogantly instructs theologians to re-interpret Scriptures that appear to contradict scientific observations.

• This Letter naturally triggered strong reactions.

Trip to Rome in 1615• In late 1615 Galileo returned to Rome to defend himself against

the arguments in circulation against him and to convince the Church authorities of the validity of the Copernican cosmology.

• It was quite a different reception from his enthusiastic treatment in 1611: no one wanted to see him.

• He did see his friend Cardinal Barberini, who explained that the problem was Galileo’s argument that there is a single unique explanation for natural phenomena.

• God’s omnipotence would make it possible that any one of many possible causes could lead to the same effect.

• Absolute truth, i.e. knowledge of reality, comes from God alone, and the Church is the authority.

Rejection of Copernicanism

• At this time the consultants reported on their two assigned questions:

! The Sun is the center of the world and hence immovable of local motion.

! The Earth is not the center of the world, or immovable, but moves according to the whole of itself, also with a diurnal motion.

• They found these propositions to be “foolish and philosophically and formally heretical.”

• They did issue a statement that astronomers may use “false and imaginary principles” to “save the appearances” (i.e. to explain astronomical phenomena).

• Galileo’s name did not appear in their report.

Bellarmino’s audience

• Cardinal Bellarmino, the chief theologian, met with Galileo privately to inform him of the consultants’ finding before it was publicly issued.

• Galileo asked for, and received from Bellarmino, a statement of the proceedings of his audience.

• It says Galileo was informed of the contents of the decree, and that he has not been reprimanded or asked to do any kind of penance.

• There is no specific injunction that Galileo must not hold or defend Copernican ideas.

• This statement becomes a controversial part of the story in 1633 in Galileo’s appearance before the Inquisition.

The New Pope• In 1623 Cardinal Barberini was elected as the

new pope, Urban VIII.

• Galileo went to Rome to join in the papal celebrations.

• He had six long audiences with the Pope.

• The Pope sent letters to the Medicis with his approval for Galileo to write an impartial treatise on the two world systems, as long as he did not go beyond mathematical & astronomical arguments.

• The Pope emphasized again to Galileo that God’s omnipotence would make it possible that any one of many possible causes could lead to the same observed effects.

Dialogue on the Two Chief World Systems

• Galileo finished the MS in 1630, and it was given a Church imprimatur in Rome & Florence.

• It is a dialogue among Salviati, Simplicio and Sagredo.

• Simplicio argues in favor of the Aristotelean-Ptolemaic system.

• Salviati argues in favor of the Copernican system.

• Sagredo is the intelligent but neutral questioner.

• It is brilliant & entertaining.

Dialogue on the Two Chief World Systems

• The book was published in Italian in a large print run in Feb 1632, and it was hugely successful.

• It was a devastating case against the Aristotelean cosmos and a strong case for the Copernican cosmos.

• Unfortunately, the Pope’s words about God’s omnipotence were put in the mouth of Simplicio, on the very last page of the Dialogue!

• The Church ordered publication ceased in Aug 1632.

• Galileo was called before the Roman Inquisition.

• In 1633 he went to Rome and stayed at the villa of the Tuscan ambassador in Rome.

Galileo in later life

Villa Medici in Rome

Political context• The Church was recovering from the Protestant Reformation.

• The Council of Trent (over ca. 25 years) developed a set of new principles to guide the Church forward.

• The Church had become a more authoritarian, centralized bureaucracy.

• In contrast to the Protestants, the Catholic Church emphasized that it is the final authority on interpretation of the Scriptures.

• The Thirty Years War was raging--initially between Catholic and Protestant countries, but now involving much of Europe.

• The Pope was accused of being weak, and was under threat of assassination for his failure to support either side in the War.

The Prosecutor’s case

• The Prosecutor produced a notarial memo from the files summarizing Galileo’s meeting with Bellarmino in 1616, which said he was issued an injunction not to “hold, teach, or defend in any way, either verbally or in writing” the Copernican system.

• Note that the case against Galileo is disobedience and not whether or not the Copernican model is correct.

• This memo is unsigned and unwitnessed, and completely outside the normal procedural rules.

• Galileo then produced the letter, signed by Bellarmino, which said only that he had been informed of the decree that the Copernican doctrine is “contrary to the Holy Scriptures and therefore cannot be defended or held.”

• There was no record of this document in the Vatican files!

The plea bargain• In view of this evidence the Prosecutor’s case collapsed,

and he asked the Cardinals for permission to agree a plea bargain with Galileo.

• He and Galileo did agree such a bargain, which saved face for everyone involved (Galileo is 69 and in ill health).

• But the Pope would not accept this.

• In June Galileo was summoned before the Inquisition, told that he had held that the Earth moved and the Sun is the center of the world, which is contrary to Holy Scripture, and he was found guilty of heresy.

• Only 7 of the 10 cardinals comprising the Inquisition signed the decree.

• Galileo read the abjuration statement, which was pro forma.

Final years

• Galileo was put under the supervision of his friend the Bishop of Siena for the next five months.

• He had a stream of visitors, including Milton & Descartes.

• In Dec 1633 Galileo was allowed to return to his villa in Arcetri in the hills above Florence.

• There he wrote his greatest scientific work, Discourses on Two New Sciences, which laid the foundation for the modern theory of motion (mechanics).

• He was surrounded by friends, visitors, and his son when he died in 1642.

• He was eventually buried with a magnificent tomb, opposite the tomb of Michelangelo in Santa Croce, Florence.

Florence: Santa Croce• The Grand Duke

wanted a tomb for Galileo opposite Michelangelo’s in Santa Croce.

• But the Church would not approve and he was buried in an inconspicuous room underneath the bell tower.

Galileo’s monument

• The Church did approve Galileo’s monument in 1732.

• It is opposite Michelangelo’s monument in Santa Croce.

Recommended reading

• Galileo’s Daughter, by Dava Sobel.

• The Crime of Galileo, by Giorgio de Santillana.

• Galileo’s “Letter to the Grand Duchess Christina,” in Discoveries and Opinions of Galileo, ed. Stillman Drake.