Scientists of the Scientific Revolution

Clockwise from top: Kepler, Copernicus, Newton, Galileo, Descartes, and Ptolemy

Astronomy

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Historical figures in the Copernican Revolution

Ptolemy – the geocentric model, that the Earth is at rest at the center of the Universe.

Copernicus – published the heliocentric model.

Galileo – his observations by telescope verified theheliocentric model.

Kepler – deduced empirical laws of planetary motion from Tycho’s observations of planetary positions.

Newton – developed the full theory of planetary orbits.

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The Copernican Revolution

The Geocentric Theory vs. The Heliocentric Theory

The Geocentric Theory

• The earth is located at the center of the universe and all the planets revolve around the earth.

Geocentric Cont…..• The Geocentric theory was believed by

the Catholic church especially because the church taught that God put earth as the center of the universe which made earth special and powerful.

• The idea of the Earth actually moving was widely felt as a foolish suggestion because, as they saw it, if the Earth was moving they would be able to feel it.

Aristotle (384-322 B.C.)• Developed an early model

based on the concept of uniform circular motion. He placed the earth at the center of the universe and all of the planets, sun and stars around it.

• When Aristotle lived, if a person could “reason” out why something happened, then you didn’t need to do any experiments to see what would happen.

Scientific Revolution” Helio-Centric Theory of the Universe

• Sun at the center of the universe,

with the planets orbiting the sun • Created by Nicholas

Copernicus (1473-1543),

a Polish astronomer

• In the realm of change, the natural motion of earthy materials was to seek the center of the universe.

• This is why Aristotle placed the earth at the center of the cosmos.

• This is also his explanation for why objects fall when dropped.

• A dropped object is just following its natural tendency to seek the center of the universe.

• Aristotle reasoned that if the earth rotated about its axis, we should fly off into space. Since we don't, the earth must be stationary.

• It would be almost 1900 years before Galileo introduced the concepts of gravity and inertia that explain why these effects are not observed even though the earth does move.

Ptolemy (140 A.D.)

• Ptolemy advanced the geocentric theory in a form that prevailed for 1400 years.

• He added mathematics to support the theory

How did Ptolemy Explain this Problem?

• Ptolemy used geometric models to predict the positions of the sun, moon, and planets, using combinations of circular motion known as epicycles.

• An epicycle is an orbit within an orbit• Having set up this model, Ptolemy then

went on to describe the mathematics which he needed in the rest of the work.

Ptolemy’s Model –

Epicycles Included

The Heliocentric Theory

• The Sun is the center of our solar system

Copernicus (1473-1543)• Polish astronomer who

advanced the theory that the Earth and other planets revolve around the Sun. This was highly controversial at the time.

• The Ptolemaic model had been widely accepted in Europe for 1000 years when Copernicus proposed his model.

Early scientists

• Made significant contributions in astronomy, physics and math• Began to explain complexities of solar system, limits of physical world• Nicolaus Copernicus, Polish astronomer, among first

Copernicus’ theory

• Idea of earth orbiting sun was not completely new• Copernicus developed detailed mathematical explanation of process• Was first scientist to create complete model of solar system

Copernicus

• Found geocentric theory of movement of sun, moon, planets not accurate• Concluded sun, not earth, near center of solar system• Heliocentric theory, earth revolves around sun

Discoveries in Astronomy, Physics, and Math

Weaknesses of theory

• Mathematical formulas did not predict positions of planets well

• Copernicus did not want to be ridiculed for weaknesses

• Died 1543 after work published, other scientists expanded on ideas

On the Revolutions of the Heavenly Spheres

• Copernicus’ famous book not published until last year of his life

• Knew church would oppose work

• Work contradicted teachings of church

• Copernicus was told by many scholars that he should make his new findings accessible to others by publishing it.

• In 1543 the book called "On the revolutions of the heavenly bodies" was released.

• Copernicus's book had a great impact that angered the Catholic and Protestant Church.

• The Church became so angry – the Geocentric theory made human beings seem closer to God and since earth was in the center that meant humans were more special.

• The heliocentric theory changed that perspective completely, making humans lose that position in the universe.

Nicholas Copernicus (1473-1543)

• Polish priest studied in Italy• returns to Poland and works on

Astronomy• writes De Revolutionibus Orbitum

Coelestitum (On the Revolutions of Heavenly Spheres)

• Earth is just another planet with a 24 hour rotation

• retains circular planetary motion (perfection of the sphere).

Copernicus• On the Revolutions of the Heavenly

Spheres.• Proposed a sun-centered view. (helio-

centric)• Universe consisted of 8 spheres. • Planets including earth rotated around

the sun but the moon revolved around the earth.

• Apparent revolution of the sun and stars around the earth was due to the rotation of the earth.

• Did not reject the Ptolemaic vision of the fixed spheres.

• His views did not make a big splash either pro or con, but there was growing dissatisfaction with the Ptolemaic view.

Nicolaus Copernicus(1473-1543)

• Polish astronomer and mathematician

• Introduced to scientific world when he attended the University of Krakow in Poland in 1492

• Appointed as a canon in the cathedral of Frauenburg where he remained for the rest of his life

• Rheticus, a student Copernicus took on in 1539, convinced Copernicus to allow him to publish his works before death

Copernicus’s Scientific Theories:

• Considered the founder of modern science

• Believed that the earth was round and the earth revolved around the sun (contrary to popular belief)– The heliocentric theory was not new, but Copernicus established the

mathematical basis

• To avoid the risk of persecution, excommunication, or imprisonment because his were revolutionary and contrary to church beliefs, Copernicus worked in privacy for more than 30 years; just before his death, friends helped to published his work

• Copernicus’s theory was first taught in several universities in the 1500s and permeated the scientific world by 1600

Copernicus Cont:• “Finally we shall place

the Sun himself at the center of the Universe. All this is suggested by the systematic procession of events and the harmony of the whole Universe, if only we face the facts, as they say, 'with both eyes open’.”- Copernicus

“The earth also is spherical, since it presses upon its center from every direction.”-Copernicus

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Nicolaus CopernicusThe Earth moves, in two ways.• It rotates on an axis (period = 1 day).• It revolves around the sun (period = 1 year).

The Copernican Universe

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The reasons for seasons – the Earth travels around the sun, and its axis of rotation is tilted by 23.5 degrees to the plane of the orbit. In July, the northern hemisphere is getting more sunlight than in January.

The heliocentric model

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The Copernican Model

Giordano Bruno: 1548 – 1600 AD

• Italian monk• Believed Copernicus

was right and that the earth revolved around the sun

• Believed the earth was alive because it moves through space

• Believed the universe is huge and everything is made up of atoms

• He did not do original research; just used reason and speculation.

• Bruno wandered around Europe teaching and writing for a living.

• He returned to Italy and found trouble

Bruno vs the Inquisition

• Bruno had been offered a teaching job in Venice and thought his employer would protect him.

• Instead, Bruno was arrested by the Inquisition for not supporting the Geo-Centric Theory

• After seven years in prison, Bruno was tried as a heretic.

• On February 6, 1600, he was burned at the stake for his scientific ideas.

The Baroque Setting• In the 1600s church through counter-

reformation much stricter

• G. BRUNO (Italian; 1548) proposes that the Sun is just one star out of an infinite number burned at the stake for heresy 1600

• 30 Years War (1618-1648) between religions

• New inventions: telescope, air pump, etc.

Tycho Brahe

Believed geocentric uni-verse is Scriptural

Built equipment to prove Copernican model wrong

Greatest naked-eye astronomer of all time

Proposed a geocentric model that saved all appearances

Tycho Brahe(1546-1601)

• Danish astronomer• Established an observatory

to study heavenly bodies• Accumulated a lot of data

on planetary movements• His tables of astronomical

observation was used by Kepler to prove Copernicus’s

helio-centric hypothesis

Brahe Cont: • Believed that the development of astronomy relied on

accurate observation• Made lots of astronomical observation with the naked

eye• Built and calibrated numerous new instruments

including:• Created a domicile and observatory which he called

Uraniborg

Tycho Brahe’s original model

ModifiedTychonicModel

Brahe Cont.

Uraniborg

Instrument to measure angles

Instrument for measuring altitude

Azimuth Quadrant made in 1577.

Tycho Brahe – The Data Taker

• Key question: Where are things?

• Catalogued positions of planets in Uraniborg and Prague

• Working without telescope• Data ten times as accurate as

before• Died at banquet binge drinking

Tycho Brahe (1546–1601)

Tycho Brahe - An Observer

• Tycho Brahe was a prominent scholar and aristocrat in Denmark in the mid-late 1500's

• He made a huge number of observations of the stars and planets, all with the naked eye– Even without a telescope, he was

very accurate in his measurements

• Also recorded the appearance of comets and supernovae– The Tycho supernova remnant is

still visible today

Tycho (1546-1601)

Tycho Brahe• collects detailed and accurate (1-

2’ accuracy) observations of stellar and planetary positions over a period of 20 years

• His research costed 5-10% of Danish GNP

• shows that comets and novas are extralunar contrary to Aristotle

• Shows that stars can change (Supernova of 1572)

Tycho Brahe observing

Brahe, Danish Astronomer• Wrote book proving bright object over Denmark sky was newly visible star• Called it supernova, distant exploding star suddenly visible on earth• Book impressed Denmark’s King Frederick II• Gave Brahe money to build two observatories

• Brahe used observatories

• Developed system to explain planetary movement

• Believed sun revolved around earth

• Other five known planets revolved around sun

Observations

• Hired as Brahe’s assistant to form mathematical theory from measurements of planets

• Published result of measurements of orbit of Mars after Brahe’s death

Kepler, German Mathematician

Brahe and Kepler

Johannes Kepler - A Theorist

• Shortly before his death, Tycho began working with another scientist named Kepler

• Kepler was put to the task of creating a model to fit all of Tycho's planetary data

• Kepler spent the remainder of his life formulating a set of laws that explained the motion of the planets

Kepler (1571 - 1630)

Kepler’s Beginnings

• Astrologer and Mystic• Tried to find “music in

the skies”• Tried to explain

distances of the 5 known planets by

spheres resting on the 5 mathematical bodies

pre-scientific

Johannes Kepler (1571-1630)

• Student of mathematics and astronomy• studied with Tycho Brahe• tested hypothesis after hypothesis until he

determined that planets move in ellipses• Three Laws of Planetary Motion

1 planets move in ellipses with sun as one focus2 velocity of a planet is not uniform3 equal area of the plane is covered in equal

time by the planets.

Johannes Kepler—(1571-1630)

• Built on the detailed observations of Tycho Brahe.

• Confirmed Copernicus’s heliocentric theory• Worked out the laws that governed planetary

motion.• Discovered that orbits were elliptical, not

circular.• Killed off the Ptolemaic theory of crystalline

spheres and a perfect heaven.• Opens the door to the question of what the

planets and stars are made of and what governs their motion.

Johannes Kepler(1571-1630)

• Used Brahe’s work to successfully prove Copernicus’s helio-centric model mathematically

• However, he disproved Brahe’s claim that planets move in circular motion – found that they move in ellipses

• Discovered that the speed of planets increase as they near the sun and decrease as they go away from it

• Discovered three laws of planetary motion– the planets orbit the sun in elliptical orbits; the sun is at one focus of

the ellipse– An imaginary line drawn from the center of the sun to the center of a

planet will sweep out equal areas in equal intervals of time– The ratio of the squares of the periods of any two planets is equal to he

ratio of the cubes of their average distance from the sun • Worked in optics, discovered two new regular polyhedra,

created the first proof of logarithms, and created a way to find the volume of solids of revolution (which influenced calculus)– Proof of logs based off of the work of Napier and Euclid

Kepler Cont.:

• Very religious (protestant); believed in Intelligent Design, and that God made the Universe according to a mathematical plan – Math was considered a way to find truth, so Kepler

thought that this gave man a way to find and understand the truth of the Universe

• Worked as an aide to Tycho Brahe and continued Brahe’s work and used it in his own work

• Established the idea of observational error

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Johannes Kepler (1571 – 1630) … discovered three empirical laws of planetary motion in the heliocentric solar system

1. Each planet moves on an elliptical orbit.2. The radial vector sweeps out equal areas in equal

times. 3. The square of the period is proportional to the cube

of the radius.

(needed for the CAPA)

Kepler’s First Law

The orbits of the planets are ellipses, with the Sun at one focus

Kepler's First Law• Kepler first noted that the orbital

path of a planet around the Sun is an ellipse, not a perfect circle

• The Sun lies at one of the foci of the ellipse

• The eccentricity of an ellipse is a measure of how 'squished' from a circle the shape is

• Most planets in the Solar System are very close to a perfect circle– Eccentricity, e ~ 0 for a circle

Focus Focus

Kepler's 1st Law: The orbital paths of the planets are

elliptical with the Sun at one focus.

Kepler's First Law

=closest to the Sun=farthest from the Sun

Kepler’s Second LawAn imaginary line connecting the Sun to any planet sweeps out equal areas of the ellipse in equal times

Kepler’s Third LawThe square of a planet’s orbital period is proportional to the cube of its orbital semi-major axis:

P 2 a3

a PPlanet Orbital Semi-Major Axis Orbital Period Eccentricity P2/a3

Mercury 0.387 0.241 0.206 1.002Venus 0.723 0.615 0.007 1.001Earth 1.000 1.000 0.017 1.000Mars 1.524 1.881 0.093 1.000Jupiter 5.203 11.86 0.048 0.999Saturn 9.539 29.46 0.056 1.000Uranus 19.19 84.01 0.046 0.999Neptune 30.06 164.8 0.010 1.000Pluto 39.53 248.6 0.248 1.001

(A.U.) (Earth years)

Kepler's Second Law

• Kepler also noticed that the planets sweep out equal areas in their orbit over equal times

• Notice that this means the planet must speed up and slow down at different points

• If it takes the same amount of time to go through A as it does C, at what point is it moving faster?– C, when it is closest to the

Sun

Kepler's 2nd Law: An imaginary line connecting the Sun to any planet sweeps out equal areas

of the ellipse over equal intervals of time.

Kepler's Third Law• Finally, Kepler noticed that

the period of planet's orbit squared is proportional to the cube of its semi major axis

• This law allowed the orbits of all the planets to be calculated

• It also allowed for the prediction of the location of other possible planets

32 aP Kepler's 3rd Law Simplified

NOTE: In order to use the equation as shown, you must be talking about a planet in

the Solar System, P must be in years, and a must be in

A.U. !!!

Kepler's Third Law - Examples

• Suppose you found a new planet in the Solar System with a semi major axis of 3.8 A.U.

• A planet with a semi major axis of 3.8 A.U. would have an orbital period of 7.41 years

32 aP

872.548.3 32 P

41.7872.54872.54 21

P years

Kepler's Third Law - Examples

• Suppose you want to know the semi major axis of a comet with a period of 25 years

• A planet with an orbital period of 25 years would have a semi major axis of 8.55 A.U.

23 Pa

6252523 a

55.8625625 331

a A.U.

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How did Kepler determine the planetary orbits?

Compare the heliocentric model to naked-eye astronomy

The most complete data had been collected over a period of many years by Kepler’s predecessor, Tycho Brahe of Denmark.

The inner planet is Earth; the outer one is Mars. Plot their positions every month. Mars lags behind the Earth so its appearance with respect to the Zodiac is shifting.

Earth

Mars

KEPLER

“And to us Jupiter, like Mars, and in the morning Mercury and Sirius, appeared four-cornered. And one of the diameters running between the corners was blue, the other red, in the middle the body was yellow, and amazingly bright.Account of personal observations...:”

Instrument to show relative distances of planets according to Copernican

System

Kepler’s Solution

Kepler solved main problem of Copernican theory

• Copernicus assumed planets orbited in circle

• Kepler found assumption untrue

• Proved planets orbited in oval pattern, ellipse

• Wanted to prove Copernicus wrong, instead proved heliocentric theory correct

• Kepler’s mathematical solar system model also correct

Galileo on Scripture:

The Scriptures teach us how to go to heaven, not how the

heavens go.

Galileo (1564-1642)• An Italian scientist, Galileo

was renowned for his contributions to physics, astronomy, and scientific philosophy.

• He is regarded as the chief founder of modern science.

• Galileo was condemned by the Catholic Church for his view of the cosmos based on the theory of Copernicus.

Galileo Galilei – The Experimentalist

Did experiments (falling bodies) rather

than studying Aristotle

Major Works• Siderius Nuntius (1610)• Dialogue concerning the Two

Chief World Systems (1632)

The latter discusses Copernicus vs Ptolemy ban by Church (1633)

– revoked by pope 1992 (1564–1642)

Galileo’s Places• Born at Pisa, Tuscany• Childhood in

Florence, Tuscany• Studies at University

of Pisa• Begins teaching at

Pisa• Gets a position at

Padua, Province of Venice

• Stays for 18 years

Galileo’s Places (cont’d)• Returns to Florence,

Tuscany in 1610 under Grand duke Cosimo II.

• 1633: Trial in Rome• From 1633: house

arrest in Acetri, near Florence

• 1637: loses eyesight• 1992: ban on Galileo

lifted by Pope John Paul II.

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Galileo’s discoveries in Astronomy

Galileo did not invent the telescope, but when he heard about the invention he figured out how to build telescopes. He had the best telescopes of his time. He was the first person to use telescopes to look at the heavenly bodies. He was first, so he made the discoveries.

Craters and mountains on the moon Moons of Jupiter Phases of Venus The Milky Way consists of innumerable stars. Sunspots move across the sun’s face.

All of these favored the Copernican (heliocentric) model.

Galileo Galilei (1564–1642)• Astronomical observations that

contradict Aristotle:– Observed mountains on the Moon,

suggesting that the Earth is not unique– Sunspots; suggests that celestial bodies

are not perfect and can change– Observed four moons of Jupiter; showed

that not all bodies orbit Earth

– Observed phases of Venus (and correlation of apparent size and phase); evidence that Venus orbits the Sun

• Also observed– the rings of Saturn– that the Milky Way is made of stars

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Galileo’s sketch of the moon as seen from his telescope

A photograph of the moon

“What do you think of the foremost philosophers of this university? In spite of my oft repeated efforts and invitations, they have refused, with the obstinacy of a glutted adder, to look at the planets or Moon or my telescope.” (letter to Kepler)

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Galileo made many specific discoveries in astronomy, through observations by telescope.

The general implications…

● The planets are objects like the Earth – masses – rather than some kind of special heavenly objects. Or, to put it another way, the Earth is just another planet.

● The planets, including Earth, travel around the sun.

● The Universe is a lot bigger than we can see by the naked eye.

These ideas could be dangerous.

Galileo Galilei (1564-1642)

• Astronomy– used a telescope, proved the heavens are not perfect (craters on moon)– supported Heliocentric system

• Laws of Motion– dropping weights from the Tower of Pisa– imagined motion without constraint!!!!– Thought of inertia

• Problems with the church– argues for separation of science and theology because we are endowed with

reason– 1633 banned by Church and house arrest– must recant heliocentric system to save neck.

Galileo’s Books• Galileo published his discoveries and support

for the Copernican model in two books published in 1616 and 1632.

• Galileo was unusual for the time because he wrote in Italian rather than Latin like most scholars.

• Galileo also took great pains to make his books interesting often writing them in the form of dialogues rather than dry, boring dissertations.

• After his first book, "Starry Messenger", was published he was warned by the Church not to publicly support Copernicism again.

Reactions to Galileo

• Italy and Spain• More freedom in France, England and Holland• University of Padua was under Venice, the most anti-

clerical state in Europe; Copernicus, Galileo and Harvey studied there

• Protestants as hostile as Catholics on Biblical grounds, less state control in Protestant nations and in the end Protestant nations become more liberal than at first.

Galileo Galilei: 1564 – 1642AD

• Italian

• Was a Professor of Mathematics at Pisa University

• Became interested in science after reading the works of Copernicus and Bruno

• These books convinced him that the earth revolved around the sun.

• He also made huge discoveries in physics.

• He proved that a pendulum swings the same time no matter the size.

• He used mathematical rules to explain this; it was the first time math had been used to describe an object in motion.

Galileo• In 1609, he switched

from being a physicist to being an astronomer.

• He heard about the newly-invented telescope and built his own.

• He used it to discover 4 moons of Jupiter and the mountains on the moons.

• These discoveries proved once again that Aristotle’s theories were wrong.

• The moon wasn’t a perfect round ball as the ancient Greeks believed, but had bumps and craters.

Galileo Continued

• Watched as the planets Venus and Saturn travel around the sun

• This proved that the Earth was not the center of the solar system.

• Galileo wrote a book in 1610 about his discoveries

• This is where his trouble with the Catholic Church begins.

Galileo Galilei:• In 1609 Galileo built his own telescope to

observe the night skies • Galileo worked with Kepler who discovered

by using convex lens it would increase the magnification

• Galileo’s telescope developed in 1609, modeled based off other telescopes

• Could magnify three times more than other telescopes; his later telescope magnified twenty times

• He could see the moon, four satellites, a supernova, the phases of Venus, and sunspots

Galileo Galilei (1564-1642)• First European to make

systematic observations of the heavens using a telescope.

• Established that the planets were made of material stuff quite similar to the earth.

• The Starry Messenger. • Publicized the shift in scientific

thinking away from the Ptolemaic view.

Galileo Galileo (1564-1642)

• The Starry Messenger– Published in 1610– Stunned contemporaries and did more to make

Europe aware of the new picture of the universe than the mathematical theories of Copernicus and Kepler

• Galileo, the Church and Inquisition• Dialogue on the Two Chief World Systems:

Ptolemaic & Copernican• Placed under house arrest and during his final

eight years Galileo studied mechanics discovering the principles of inertia & force

Galileo’s Theories

• Brought him into direct conflict with the church• Church leaders pressured him not to support ideas of Copernicus• Dialogue concerning Two Chief World Systems, 1632, showed

support

House Arrest

• Galileo stated would not use Copernican theory in work• Received lenient sentence in return• Pope ordered Galileo under house arrest, where he spent rest of life

Trial

• Pope Urban VII ordered Galileo to Rome to stand trial before Inquisition• Church wanted to stamp out heresy, or dissenting views• Trial held, April 1633

Science and the Church

Trial Before the Inquisition

• Galileo abided by this edict until 1632 when he published "A Dialogue on the Two Chief World Systems". This book's outright support for the Copernican model and its ridiculing of the Ptolemaic model earned Galileo a trial before the Inquisition.

• Galileo was accused of heresy and sentenced to house arrest for life. However, he got off easily compared to fellow Italian Giordano Bruno who was burned at the stake in 1600 for teaching Copernican ideas.

Galileo and the Church• In 1616, Galileo promised

to give up his ideas. • But he then published a

book making fun of the Catholic’s teaching of the Geo-Centric Theory.

• In his book, he uses a fictional dialogue or conversation to make fun of the Church.

• The character who backed the Church’s views was called Simplicius, which means stupid.

• In 1633 after a series of warnings against his teaching, Galileo was put on trial before the Inquisition

• The charge was heresy with the likely punishment of death

• He was 70 years old at the time

Galileo’s Letter to Castelli

“I am inclined to think that the authority of Holy Scripture is intended to convince men of those truths which are necessary for their salvation, and which being far above man's understanding cannot be made credible by any learning, or any other means than revelation by the Holy Spirit.  But that the same God has endowed us with senses, reason, and understanding, does not permit us to use them, and desires to acquaint us in any other way with such knowledge as we are in a position to acquire for ourselves by means of those faculties, that it seems to me I am not bound to believe, especially concerning those sciences about which the Holy Scriptures contain only small fragments and varying conclusions; and this is precisely the case with astronomy, of which there is so little that the planet are not even all enumerated....”

Galileo and the Church• Some historians

believe Galileo was tortured, because he suffered from weakened muscles in his gut from the stretching rack.

• Others say he was just shown the torture chamber to scare him.

• To save his life, Galileo confessed that the Earth did not go around the sun.

• According to legend, he muttered under his breath: “But it still moves.”

• He was sentenced to life imprisonment and ended up locked in his own home where he went blind and had to give up his scientific work.

Galileo the Heretic• Church found his findings

dangerous. Why?– Removed Humans from the center

of the earth, – Did away with the perfection of

circular orbits and – No longer had God in a fixed place.

• Inquisition condemns this view; he recants under pressure.

• Is placed under house arrest for the last 8 years of he life.

• Attitude of the church crimped further scientific inquiry into the heavens in Italy

Galileo + Church:• While at the University of Padua, Galileo became very much involved with

Copernicus’s heliocentric theory of the universe

• Galileo’s invention of the telescope enabled him to make observations that supported and proved the Copernican theory and encouraged him to publicly support it

• For this and for other letters, works, etc. that criticized the scripture as simply symbolical, Galileo was summoned to Rome where he was tried by the Inquisition in 1633

– They forced him to recant his belief in the Copernican Theories

• In April of 1633 Galileo is interrogated before the Inquisition. He agrees to plead guilty to a lesser charge in exchange for a more lenient sentence.

• Galileo was sentenced to house arrest in Siena

• Only in 1992 did the Church officially admit their mistake with the Galileo Trial

• The Trial caused fear among scientists and encouraged them to keep their findings from the Church and thus from the public

• In February 1632, Galileo published his book, Dialogue Concerning the Two Chief Systems of the World – Ptolemaic and Copernican

Galileo’s Forced StatementI, Galileo, son of the late Vincenzo Galilei, Florentine, aged seventy years, arraigned personally before this tribunal, and kneeling before you, Most Eminent and Reverend Lord Cardinals, Inquisitors-General against heretical depravity throughout the entire Christian commonwealth, having before my eyes and touching with my hands, the Holy Gospels, swear that I have always believed, do believe, and by God's help will in  the future believe, all that is held, preached, and taught by the Holy Catholic and Apostolic Church. But whereas -- after an injunction had been judicially intimated to me by this Holy Office, to the effect that I must altogether abandon the false opinion that the sun is the center of the world and immovable, and that the earth is not the center of the world, and moves, and that I must not hold, defend, or teach in any way whatsoever, verbally or in writing, the said false doctrine, and after it had been notified to me that the said doctrine was contrary to Holy Scripture -- I wrote and printed a book in which I discuss this new doctrine already condemned, and adduce arguments of great cogency in its favor, without presenting any solution of these, and for this reason I have been pronounced by the Holy Office to be vehemently suspected of heresy, that is to say, of having held and believed that the Sun is the center of the world and immovable, and that the earth is not the center and moves: 

Galileo’s Abjuration before the Inquisition, 1633 …because I have been enjoined, by this Holy Office, altogether to abandon the false opinion which maintains that the sun is the center and immovable, and forbidden to hold, defend, or teach, the said false doctrine in any manner… therefore, with a sincere heart and unfeigned faith, I abjure, curse, and detest the said errors and heresies, and generally every other error and sect contrary to the said Holy Church; and I swear that I will never more in future say, or assert anything, verbally nor in writing, which may give rise to a similar suspicion of me; but that if I shall know any heretic, or any one suspected of heresy, I will denounce him to this Holy Office, or to the Inquisitor and Ordinary of the place in which I may be.

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Galileo’s sketch of the moon as seen from his telescope

A photograph of the moon

“What do you think of the foremost philosophers of this university? In spite of my oft repeated efforts and invitations, they have refused, with the obstinacy of a glutted adder, to look at the planets or Moon or my telescope.” (letter to Kepler)

Galileo

• Scenes from the Trial of Galileo

Replica of Galileo’sTelescope

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Galileo made many specific discoveries in astronomy, through observations by telescope.

The general implications…

● The planets are objects like the Earth – masses – rather than some kind of special heavenly objects. Or, to put it another way, the Earth is just another planet.

● The planets, including Earth, travel around the sun.

● The Universe is a lot bigger than we can see by the naked eyeeye.

These ideas could be dangerous.

•Galileo’s conflict with the Church: Can questions about the natural world be settled by the Bible?

•Or must they be settled by the best empirical and mathematical methods of science?

•Are we free to investigate nature, or must we be constrained by religious authority?

•The book of God: The history of God and his creation, written in a language for general human comprehension

•The book of Nature: The natural world itself, revealing its laws in the phenomena--

•--but written in the language of mathematics.

Questions Raised by Galielo

Galileo on science and Scripture:

I think it would be the part of wisdom not to allow any one to apply passages of Scripture in such a way as to force them to support as true any conclusions concerning nature, the contrary of which may afterwards be revealed by the evidence of our senses, or by actual demonstration. Who will set bounds to man's understanding ? Who can assure us that every thing that can be known in the world is known already ?

Galileo on science and Scripture (continued)

. . . I am inclined to think that Holy Scripture is intended to convince men of those truths which are necessary for their salvation, and which being far above man's understanding cannot be made credible by any learning, or by any other means than revelation. But that the same God who has endowed us with senses, reason, and understanding, does not permit us to use them, and desires to acquaint us in another way with such knowledge as we are in a position to acquire for ourselves by means of those faculties— that, it seems to me I am not bound to believe…

Galileo’s Genius

• Careful observation of a phenomenon

• Deriving conclusions from “data”

• Making new predictions

• Publishing results “for everyone” [in Italian]

• Anticipates his opponents arguments, and nullifies them by using stringent logic

Galileo’s Genius – Applied to Sunspots

• Careful observation of a phenomenon– Observes sunspots (as did others before him)– Follows them over several weeks

• Deriving conclusions from “data”– Concludes that these are things very close to the Sun’s

surface • Making new predictions

– Deduces that the sun rotates around itself in 26 days– Makes a prediction as to the Sun’s rotational axis

• Publishing results “for everyone” [in Italian]– “Letters on Sunspots” (1612)

• Anticipates his opponents arguments, and nullifies them by using stringent logic– Shows that sunspots can’t be inner planets

Saturn

• Sketch of 1616

• Engraving in “The Assayer” (1623)

Applications

• From the distance r between two bodies and the gravitational acceleration a of one of the bodies, we can compute the mass M of the other

F = ma = G Mm/r2 (m cancels out)

– From the weight of objects (i.e., the force of gravity) near the surface of the Earth, and known radius of Earth RE = 6.4103 km, we find ME = 61024 kg

– Your weight on another planet is F = m GM/r2

• E.g., on the Moon your weight would be 1/6 of what it is on Earth

Applications (cont’d)

• The mass of the Sun can be deduced from the orbital velocity of the planets: MS = rOrbitvOrbit

2/G = 21030 kg – actually, Sun and planets orbit their common center of

mass

• Orbital mechanics. A body in an elliptical orbit cannot escape the mass it's orbiting unless something increases its velocity to a certain value called the escape velocity– Escape velocity from Earth's surface is about 25,000 mph

(7 mi/sec)

Objections to the Heliocentric Model Answered

• If the Earth is moving, why do dropped objects appear to fall straight down?– Dropped objects start with the velocity of Earth

(Galileo)

• If the Earth rotates, why don't we get thrown off?– Earth's rotation isn't fast enough!

• If the Earth revolves around the Sun, why don't we observe stellar parallax?– It's there, but very small, because the stars are so far

away (Aristarchus)

• Why don't we feel the wind of our motion? – The air moves along with the Earth

• In 1992, the Roman Catholic Church finally repealed the ruling of the Inquisition against Galileo. The Church gave a pardon to Galileo and admitted that the heliocentric theory was correct. This pardon came 350 years after Galileo's death.

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The observed solar system at the time of Newton

SunMercuryVenusEarthMarsJupiterSaturn

(all except Earth are named after Roman gods, because astrology was practiced in ancient Rome)

Three outer planets discovered later…Uranus (1781, Wm Herschel)Neptune (1846 Adams; LeVerrier) Pluto (1930, Tombaugh)

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To explain the motion of the planets, Newton developed three ideas:

1. The laws of motion2. The theory of universal gravitation3. Calculus, a new branch of mathematics

Newton solved the premier scientific problem of his time --- to explain the motion of the planets.

Isaac Newton

“If I have been able to see farther than others it is because I stood on the shoulders of giants.”

--- Newton’s letter to Robert Hooke,perhaps referring to Galileo and Kepler

mF

a

221

r

mGmF

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Newton’s Theory of Universal GravitationNewton and the Apple

(The apple never fell on his head, but sometimes a stupid person will say that, trying to be funny.)

Newton asked good questions the key to his success.

Observing Earth’s gravity acting on an apple, and seeing the moon, Newton asked whether the Earth’s gravity extends as far as the moon.

William Herschel: 1782 and Caroline Herschel: 1750 – 1848AD

• Became Britain’s top astronomer

• Discovered the planet Uranus

• Found many types of new stars and comets

• 1783: Found a new type of light called infrared

• His sister, Caroline, helped her brother make the lenses for telescopes and kept his daily records.

• She went on to discover seven comets and to list all the main stars. This became a vital source of information for astronomers.

• She was awarded many medals by the Royal Astronomical Society and the King of Prussia

William and Caroline