Galileo: the first*
astronomer to use a
telescope
Early career:
Pisa & Padua
Bob Joseph
Institute for Astronomy
University of Hawaii
Early life
Padua
•
Born in Pisa in 1564 to an old & distinguished Florentine
family.
•
Galileo produced three children with his common-law
wife, a Venetian woman named Marina Gamba.
•
•
Matriculated at Univ of Pisa in 1581 to study medicine.
•
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.
•
Went home to Florence, did some teaching, and gave
several well-received public lectures on mathematics.
•
He also developed the “geometric and military compass,”
which spread his fame and brought additional income.
•
•
Appointed to Chair of Mathematics at Pisa in 1589.
•
Remained at Padua for the next 18 years.
Heard lecture on Euclid, began studying mathematics on
his own, and left the Uni without a degree in 1585.
In 1592 he successfully competed for the Chair of
Mathematics at the Univ of Padua (Republic of Venice).
Astronomical context
The 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 commonsense 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.
Galileo ca. 1610-1615
Telescopic
discoveries
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
•
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.
The Pleiades
•
•
Galileo found 36 stars in the Pleiades constellation.
•
When observing the faint band of light, the Milky Way,
he found it was composed of “numberless stars.”
!
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.”
Galileo’s astronomical
discoveries
The Sidereus Nuncius
•
By December of 1609 or early 1610 Galileo had used
his telescopes to discover:
•
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.
Inner
moons of
Jupiter
He also resolved other nebulosities know since ancient
times into clusters of individual stars.
•
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.”
Return to Florence
Move to the
Medicean Court
•
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 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.
He used his connections with the powerful Medici
family to publicize his scientific discoveries.
Saturn’s “handles”
Further telescopic
discoveries
•
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.
First trip to Rome
Conflict with the
Roman Inquisition
Anti-Galileo reaction
•
•
In 1611 Galileo made a trip to Rome.
•
•
The Jesuit Collegio Romano gave him a big banquet.
•
It was a hugely successful experience for Galileo.
He received an enormous welcome by both academics
and Church leaders.
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.
Letter to the Grand Duchess
•
Meanwhile, an anti-Galileo faction, chiefly of a few
university professors and Dominicans, had been
developing.
•
On page 2 of the Sidereus Nuncius Galileo makes his
first published statement that he accepts the suncentered cosmology of Copernicus.
•
One or two members of this group denounced Galileo to
the Inquisition.
•
•
•
Nothing came of this.
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 reinterpret Scriptures that appear to contradict scientific
observations.
•
This Letter naturally triggered strong reactions.
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.
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
•
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.
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.
!
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.
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 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.
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.
Dialogue on the Two Chief
World Systems
•
At this time the consultants reported on their two
assigned questions:
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.
Political context
Galileo in later life
Villa Medici in Rome
•
•
The Church was recovering from the Protestant Reformation.
•
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.
•
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.
•
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.
In Dec 1633 Galileo was allowed to return to his villa in
Arcetri in the hills above Florence.
The Council of Trent (over ca. 25 years) developed a set of
new principles to guide the Church forward.
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.
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.