The document discusses several important figures from the Scientific Revolution era who contributed to developments in the heliocentric model of the solar system. It describes Ptolemy's geocentric model, followed by Copernicus publishing his heliocentric theory. Galileo then used the telescope to observe evidence supporting Copernicus, while Kepler deduced his laws of planetary motion from Tycho Brahe's observations.

1. Scientists of the Scientific
Revolution
Clockwise from top: Kepler, Copernicus, Newton, Galileo, Descartes, and Ptolemy

3. Astronomy

5. 7/14/06 ISP 209 - 3A 5
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 the
heliocentric model.
Kepler – deduced empirical laws of planetary motion from Tycho’s
observations of planetary positions.
Newton – developed the full theory of planetary orbits.

6. 7/14/06 ISP 209 - 3A 6
The Copernican Revolution

7. The Geocentric Theory vs.
The Heliocentric Theory

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

9. 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.

10. 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.

11. 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

12. • 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.

13. • 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.

14. Ptolemy (140 A.D.)
• Ptolemy advanced
the geocentric
theory in a form
that prevailed for
1400 years.
• He added
mathematics to
support the theory

15. 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.

16. Ptolemy’s
Model –
Epicycles
Included

17. The Heliocentric Theory
• The Sun is the center of our solar system

18. 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.

19. 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

20. 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

21. • 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.

22. 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).

23. 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.

24. 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

25. 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

26. 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

28. 7/14/06 ISP 209 - 3A 28
Nicolaus Copernicus
The Earth moves, in two ways.
• It rotates on an axis (period = 1 day).
• It revolves around the sun (period = 1
year).

29. The Copernican Universe

31. 7/14/06 ISP 209 - 3A 31
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

32. 7/14/06 ISP 209 - 3A 32

33. 7/14/06 ISP 209 - 3A 33
The Copernican Model

34. 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

35. 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.

36. 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.

38. 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

39. 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

40. 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

41. Tycho Brahe’s
original model

42. Modified
Tychonic
Model

44. Brahe Cont.
Uraniborg
Instrument to measure angles
Instrument for measuring altitude
Azimuth Quadrant made in
1577.

45. 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)

46. 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)

47. 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

48. 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

49. 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)

50. 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

51. 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
focus
2 velocity of a planet is not uniform
3 equal area of the plane is covered in equal
time by the planets.

52. 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.

53. 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

54. 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

55. 7/14/06 ISP 209 - 3A 55
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)

56. Kepler’s First Law
The orbits of the planets are ellipses,
with the Sun at one focus

57. 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.

58. Kepler's First Law
=closest to the Sun
=farthest from the Sun

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

60. Kepler’s Third Law
The square of a planet’s orbital period is proportional to the
cube of its orbital semi-major axis:
P 2  a3
a P
Planet Orbital Semi-Major Axis Orbital Period Eccentricity P2/a3
Mercury 0.387 0.241 0.206 1.002
Venus 0.723 0.615 0.007 1.001
Earth 1.000 1.000 0.017 1.000
Mars 1.524 1.881 0.093 1.000
Jupiter 5.203 11.86 0.048 0.999
Saturn 9.539 29.46 0.056 1.000
Uranus 19.19 84.01 0.046 0.999
Neptune 30.06 164.8 0.010 1.000
Pluto 39.53 248.6 0.248 1.001
(A.U.) (Earth years)

61. 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.

62. 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
3
2
a
P 
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. !!!

63. 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
3
2
a
P 
872
.
54
8
.
3 3
2


P
41
.
7
872
.
54
872
.
54 2
1



P years

64. 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.
2
3
P
a 
625
252
3


a
55
.
8
625
625 3
3
1



a A.U.

65. 7/14/06 ISP 209 - 3A 65
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

66. 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

67. 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

68. Galileo on Scripture:
The Scriptures teach us how to
go to heaven, not how the
heavens go.

69. 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.

70. 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)

71. 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

72. 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.

73. 7/14/06 ISP 209 - 3A 73
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.

74. 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

75. 7/14/06 ISP 209 - 3A 75
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)

76. 7/14/06 ISP 209 - 3A 76
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.

77. 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.

78. 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.

79. 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.

80. 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.

81. 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.

82. 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.

83. 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

85. 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.

86. 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

87. 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

88. 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.

90. 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

91. 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....”

92. 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.

93. 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

94. 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

95. Galileo’s Forced Statement
I, 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:

96. 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.

97. 7/14/06 ISP 209 - 3A 97
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)

98. Galileo
• Scenes from the Trial of Galileo
Replica of Galileo’s
Telescope

100. 7/14/06 ISP 209 - 3A 100
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.

101. •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

102. 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 ?

103. 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…

104. 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

105. 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

106. Saturn
• Sketch of 1616
• Engraving in “The Assayer” (1623)

107. 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 = 6.4103 km, we find ME = 61024 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

108. Applications (cont’d)
• The mass of the Sun can be deduced from
the orbital velocity of the planets: MS =
rOrbitvOrbit
2/G = 21030 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)

109. 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

110. • 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.

111. 7/14/06 ISP 209 - 3A 111
The observed solar system at the time of Newton
Sun
Mercury
Venus
Earth
Mars
Jupiter
Saturn
(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)

112. 7/14/06 ISP 209 - 3A 112
To explain the motion of the planets, Newton developed three
ideas:
1. The laws of motion
2. The theory of universal gravitation
3. 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
m
F
a 
2
2
1
r
m
Gm
F 

113. 7/14/06 ISP 209 - 3A 113
Newton’s Theory of Universal Gravitation
Newton 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.

114. 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

115. William and Caroline