asta01 at utsc – lecture 9

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ASTA01 at UTSC – Lecture 9

Chapter 3The Origin of Modern Astronomy

-Ancient astronomy-The Copernican revolution

-De Brahe and Kepler-Galileo-Newton

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.

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• 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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• 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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• 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.

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,

arethe four largest moons of Jupiterknown as its Galilean satellites

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• 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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• 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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• 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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• 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.


• 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.


• 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

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• 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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• 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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• 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.

Galileo’s “1st trial”

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Censorship

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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

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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

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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.

asta01 at utsc – lecture 9

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