Transcript The Scale of the Cosmos

ASTA01 at UTSC – Lecture 9
Chapter 3
The Origin of Modern Astronomy
-Ancient astronomy
-The Copernican revolution
-De Brahe and Kepler
-Galileo
-Newton
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Galileo Galilei (1564-1642)
• Galileo Galilei was born in the Italian city of
Pisa, and studied medicine there but later convinced
his father that he should study mathematics and
natural science (i.e., physics).
• He discovered that the pendulum swings with a period
independent of how far it is deflected, constructed
thermometer etc.)
• Eventually, he became professor
of mathematics at the
university at Padua, where he
remained for 18 years.
• During this time, Galileo adopted
the Copernican views.
Telescopic Observations
• It was the telescope that drove Galileo to
publicly defend the heliocentric model.
• Galileo did not invent the telescope.
• It was apparently invented around 1608 by lens
makers in Holland.
• Galileo, hearing
descriptions in the Fall of
1609, was able to build
working telescopes in his
workshop.
Telescopic Observations
• Also, Galileo was not the first person to
look at the sky through a telescope.
• However, he was the first to observe the sky
carefully and apply his observations to the
main theoretical problem of the day: the place
and nature of Earth among planets
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Telescopic Observations
• What Galileo saw through his telescopes
was so amazing that he rushed a small
book into print, Sidereus Nuncius (The
Starry Messenger).
• In the book, he reported two major
discoveries about the solar system.
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Telescopic Observations
• First, the Moon was not perfect. (Aristotle’s
philosophy held that the Moon was
perfect)
• It had mountains and valleys on its surface.
• Galileo used the shadows to calculate the height of
the mountains.
• Galileo showed that it was a world like Earth,
• This put a division of the world into heaven
and earth, two completely different realms,
into question.
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Telescopic Observations of Jupiter & moons
• Second, Galileo’s
telescope revealed four
new ‘planets’ circling
Jupiter.
• Today, these ‘planets’
are known as the
Galilean moons of
Jupiter
• 3 have underground
oceans of water, 1 has
active volcanoes
By Galileo, Jan 7-24, 1610
Siderius Nuncius (1610)
Medicean ‘stars’ (Medicea
Sidera)
Were announced as ‘planets’,
In fact they are neither:
Io, Europa,
Ganimedes and Callisto,
are
the four largest moons of Jupiter
known as its Galilean satellites
Telescopic Observations
• The moons of Jupiter supported (but not
proved!) the Copernican model over the
Ptolemaic model.
• Critics of Copernicus had said Earth could not
move – because the Moon would be left
behind.
• However, Jupiter moved and kept its satellites.
Galileo's discovery suggested that Earth, too,
could move and keep its Moon.
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Telescopic Observations
• Also, Aristotle’s philosophy included the
belief that all heavenly motion was centred
on Earth.
• Galileo showed that Jupiter's moons revolve
around Jupiter: there could be centres of
motion other than Earth!
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Telescopic Observations
• Galileo noticed the P vs. a relation (period
vs. distance) : Jupiter's innermost moon
had the shortest orbital period and the
moons further from Jupiter had
proportionally longer periods.
• In this way, Jupiter’s moons made up a
harmonious system ruled by Jupiter – just as
the planets in the Copernican universe were a
harmonious system ruled by the Sun.
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Telescopic Observations
• This similarity didn’t constitute proof
• Nevertheless, Galileo saw it as an indication
that the solar system could be Sun-centred
and not Earth-centred.
• In the years of further exploration with his
telescope, Galileo made additional fundamental
discoveries.
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Telescopic Observations
• When he observed Venus, he saw that it
was going through phases like those of the
Moon.
• In the Ptolemaic model, Venus moves around
an epicycle centred on a line between Earth
and the Sun.
• If that were
true, it
would
always be
seen as
a crescent.
Telescopic Observations
• However, Galileo saw Venus go through a
complete set of phases, including full and
gibbous. This proved that it did indeed
revolve around the Sun:
• a proof of either Tychonic or Copernican
system
Telescopic Observations
• Sidereus Nuncius (1610) was popular and
made Galileo famous.
• In 1611, Galileo visited Rome and was treated
with great respect.
• He had friendly discussions with the powerful
Cardinal Barberini, supporter of arts and sciences,
a later pope Urban VIII
• Church officials and Jesuit priests supported him
• Civil authorities as well
• The largest opposition was offered by Academia
(university scientists)
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Galileo Galilei applies for another ‘grant’
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Telescopic Observations
• However, as he was outspoken, forceful,
and sometimes tactless, he offended
many important people who questioned
his telescopic discoveries.
• Some critics said he was wrong.
• Others said he was lying.
• Some refused to look through a telescope lest
it mislead them (one particular philosopher)
• Others looked and claimed to see nothing –
hardly surprising given the awkwardness of
those first telescopes.
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Galileo’s “1st trial”
• When Galileo visited Rome again in 1616,
Cardinal Bellarmine interviewed him
privately and ordered him to cease public
debate about models of the universe.
• Galileo appears to have mostly followed the
order.
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Censorship
• The Inquisition (formally named the
Congregation of the Holy Office the Index)
banned books relevant to the Copernican
hypothesis.
Censorship and control over printing presses was a
common phenomenon in the secular and church
domains alike, in the 1500- and 1600’s. (In England,
only 2 universities and 21 printing offices were
approved and licensed by the crown, with a total of
53 presses).
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What happened with De revolutionibus
• De Revolutionibus itself was only
suspended for a few years pending revision
of places where strong but unsupported
claim were made and/or it went too much
into religious perspective.
• It was recognized as useful for its
predictions of planet positions and allowed
into circulation after the modifications.
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De revolutionibus
• Everyone who owned a copy of the book was
required to cross out certain statements and
add handwritten corrections that stated the
Earth’s motion and the central location of the
Sun were only theories and not facts.
• This is a situation that you will recognize as
recurring today in connection with textbooks
discussing biological evolution.
• Heliocentric theory was indeed a theory not
properly proven by observational evidence
• Tycho Brahe’s geo-heliocentric system was
explaining observed phenomena just as well.
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Dialogo and Trial
• In 1623 Galileo’s friend Cardinal Maffeo Barberini
became Pope, taking the name Urban VIII.
• Galileo went to Rome in an attempt to have the
1616 order to cease debate lifted. The attempt
was unsuccessful
• Nevertheless, Galileo began to write a massive
defence of Copernicus’s model, completing it in 1629.
• After some delay, Galileo’s book was approved by
both the local censor in Florence and the head censor
of the Vatican in Rome.
• It was printed in 1632.
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Dialogo
• The book was called Dialogo Dei Due
Massimi Sistemi (Dialogue Concerning the
Two Chief World Systems).
• It confronted the ancient astronomy of
Aristotle and Ptolemy with the Copernican
model.
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Dialogo
• Galileo wrote the book as a debate among
three friends.
• Salviati is a swift-tongued defender of
Copernicus.
• Sagredo is intelligent but largely uninformed.
• Simplicio is a dim-witted defender of Ptolemy.
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Dialogo
• The book was a clear defence of
Copernicus.
• Some claims were not supported by
evidence, although intentionally or not,
presented as such, for instance the
sunspots or the Earth tides.
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Dialogo and Trial
• Also, Galileo exposed the pope’s authority to
ridicule and provoked the church authorities.
• Urban VIII was fond of arguing that, as God was
omnipotent, God could construct the universe in
any form – while making it appear to humans to
have a different. Thus, observations may be
misleading.
• The pope privately asked Galileo to keep a balanced
discussion of two world systems and also to mention
his own arguments.
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Dialogo and Trial
• Galileo placed the pope’s argument in the
mouth of Simplicio.The pope took offense
and ordered Galileo to face the Inquisition.
• Galileo was interrogated by the Inquisition and
threatened with torture [no evidence of that; 4
private meetings were held. 3 out of 10 judges
declined to sign the mild sentence].
• The Inquisition condemned Galileo, not
primarily for heresy but for disobeying the
orders given him in 1616. The authorities felt
they must react to Galileo. They placed Dialogo
on the Index of prohibited works.
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Dialogo and Trial
• In 1633, at the age of 70, kneeling before the
Inquisition, Galileo read a recantation admitting
his errors.
• Tradition [or a myth] has it that as he rose he
whispered, “E pur si muove” (“Still it moves”) –
referring to Earth.
• Galileo did acknowledge that he made mistakes.
Eg., he claimed unjustly that tides or sunspots
prove Copernicus was right. In our current science
myths these proceedings are painted as a brutal
trial with threats of Guantanamo-like torture.
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Galileo before the Inquisition – artists vision only!
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The myth of Galileo as science martyr
• Although he was formally sentenced to life-long
home arrest, he was actually confined to certain
luxurious homes, including a suite with a view
toward Vatican gardens and the villa of the
ambassador of Tuscany and his own villa, where
Galileo received numerous visitors, and had an
active social and scientific life.
• His daughter was a nun at a convent; she
overtook the second part of the sentence
according to which once oer week recantations of
4 psalms were to be made.
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The myth of Galileo as science martyr
• Not being able to write much about theoretical
astronomy (to which, unlike Kepler, Galileo did
not contribute anyway; Galileo did not even fully
believe in Kepler’s laws), the old scientist
concentrated on and achieved much later fame
by describing the subjects of kinematics and
dynamics (about motion and forces in Physics).
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Galileo
• Galileo died in 1642, 99 years after the
death of Copernicus.
• The next year, Isaac Newton was born, a man
to actually provide a large number of proofs
supporting the Copernican order of the
universe.
• 350 years later, in 1992, Pope John Paul II made a
formal statement acknowledging the unjust
condemnation of Galileo by the Catholic Church,
saying that both sided made mistakes.
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