From 1996-2001 I taught in the
Intellectual Heritage Program at Temple University in Philadelphia,
Pennsylvania. This page is part of my teaching materials for Intellectual
Heritage 51, a course covering literature and ideas from Sappho through
Dr. Janice Siegel
Location: Florence, Italy
Photo courtesy of Kathy Peters
location: near Logan Circle, Philadelphia
Up until Galileo’s
time, people believed in the geocentric (earth in the middle) cosmological view
(the composition of the universe).
philosophers (6th century BC) had already determined that the
universe was composed of four elements: air, fire, water and earth.
Aristotle (384-322 BC):
joined Plato's Academy at age 17. Became tutor of Alexander in 343 BC. The
greatest collector and organizer of knowledge in the ancient world. Aristotle's
Universe: universe is finite and spherical, with stationary earth at center. Two
sets of rules: one for earth, one for the heavenly bodies.
Earth: composed of four
elements fire and air (light and move upward) and earth and water (heavy, fall
downwards). The Earth is in the center of all things, where heavy things fall
to. Aristotle's scientific proof that the earth is a sphere: its curved shadow
on the face of the moon in eclipse; the sight of stars not seen before when one
travels north or south.
Heavens: composed of aether
- not subject to decay, immortal - just look at the perfect circular motion of
celestial bodies - immutable, no beginning, no limit. Aether is outside
our gritty experience and reality. (All of these suppositions will be disproven
by Galileo and Kepler). Two different sets of physics laws governs the heavens
and the earth. By the way, this fifth elements of aether is how the word quintessence
came to be – the "true, immortal nature" of something – its
core substance (quintus means "fifth" in Latin).
According to Aristotle,
the cosmos (universe) was a group of concentric spheres, a series of
balls within balls each having the same center. Imagine a gigantic lucite ball
with interior balls. The innermost ball, of course, is the earth (made of dirt).
The other celestial orbs are all embedded in Crystalline spheres which
revolve around the unmoving earth. You may recall that the pre-Socratic
philosopher Pythagoras (530 BC) suggested that the universe worked according to
mathematical principles (and boy, was he right. Just ask NASA). The ancients
knew of seven planets (Neptune and Pluto cannot be seen with the naked eye) and
we recall that Pythagoras (530 BC) invented the seven-tone scale (do-re-mi-fa-so-la-ti-do).
The Music of the Spheres is said to ring out clear as a bell when all
these crystalline spheres are in perfect harmony and aligned just right (the Age
of Aquarius?) Anyway, each orb is embedded in its sphere. Here is the order of
the celestial bodies revolving around the earth from nearest to farthest orbit:
moon, Mercury, Venus, sun, the outer planets and last, the fixed stars. The
ancients believed that all the stars of the night sky were as if white dots
painted on black velvet and each night the black velvet backdrop rotated in an
arc while the earth stayed motionless (well, they do all move in tandem,
or together – just watch the constellations move across the sky in groups).
Beyond the sphere of the fixed stars lay the "empyrean", the
home of angels and immortal spirits. So much for science!
Points in Favor: it
certainly seems to work. If you stand in a field all day long from before
sunrise, you will observe that the sun rises in the east, moves across
the sky, and sets in the west and the earth doesn’t move at all. Right?
The earth can’t move, or it would leave things behind, like birds and
baseballs. So for 1600 years, everyone accepted this cosmological theory
although it is WRONG! because THE SUN IS IN THE MIDDLE – THAT’S WHY WE
CALL IT THE SOLAR SYSTEM
Archimedes (287-212 BC)
might have figured out the problem here, but practical applications of
scientific theory were only allowed for military and agricultural purposes.
Galileo notes him over 100 times in his writings.
Ptolemy (100-170 AD):
during time of Hadrian's rule - encouraged learning. Rejected rotation of earth
because objects (like birds) would be left behind. His work, called The
Almagest, was written in 150 AD and is the greatest surviving astronomical work
of antiquity. Ptolemy adopted Aristotle’s model but replaced Aristotle's
spheres with a system of geometric devices (equant, epicycle...) that explained
the apparent motions in the heavens. (The crystalline sphere theory was rejected
when they realized that comets come into the solar system at an angle and would
have to break through these spheres. That's how they figured out that there
really aren't solid objects up there in which the planets are enmbedded.)
Ptolemy's work was the canonical work (the absolute last word) on cosmology for
14 centuries until Copernicus.
MEDIEVAL EUROPE: after
the fall of Rome, only Latin texts survived in the Western World (not Greek),
although Plato influenced the early Christian fathers (like St. Augustine). But
they were rediscovered by the Arab World and translated into Arabic and read
widely. (For example, Ptolemy’s work is translated into Al-majisti). In
the 9th century both Greek and Hindu scientific works were translated
into Arabic (including Ptolemy's Almagest). Scholars popularized
"Arabic" numbers (actually they were Hindu), and adopted the decimal
system and the concept of zero. Classical learning followed in the wake of
Islamic conquests that swept across North Africa then into Spain. Intellectual
freedom encouraged the interaction of Islamic, Jewish, and Christian thought.
During the 12th
century, the ideas of Aristotle, through the influence of the pantheistic Arab
philosopher Averroes, infiltrated the universities of Christendom. By the 13th
century, the complete works of Aristotle were translated into Latin.
The Church moved
quickly. St. Thomas Aquinas (1225-1274) got the very difficult job of
synthesizing Aristotelian natural philosophy with Christian theology, a
revolution of religious thought.
In other words, he had
to make Christian thought (using the Scripture as source) jive with the older
pagan understanding of the world which was taking European learning centers by
storm. And he was brilliant at it. Christianity theology teaches by
divine revelation – Greek philosophy puts all its stock in human
wisdom. Aquinas concluded that the two were compatible.
Greek natural philosophy
had concluded that the earth was (a) in the middle of the universe and (b) that
it was composed of different material than the rest of the universe. Aquinas
agreed completely, but for very different reasons. Aquinas concluded that when
God made the universe, it was absolutely perfect in every respect. His greatest
achievement – man – He placed in the center, like a jewel in a crown –
because He was so proud of it. But man screwed up. Because of the Fall (Adam and
Eve eating the fruit of the tree of Knowledge of Good and Evil as told in
Genesis 2), man sullied or dirtied the earth and everything else he touched.
That is why the earth is dirty and heavy now. It used to be perfect like
everything else. But everything else – all other celestial bodies – remain
pristine, untouched by human hands and therefore still perfect as God made them.
successfully merged Greek natural philosophy and Christian theology. The only
problem was that both are based on an incorrect premise – they are wrong. And
once scientific discoveries began showing that the earth was NOT in the middle,
the Church panicked because they had so carefully intertwined their theological
doctrine with that cosmological model that it was like a giant JENGA game – if
you took that one piece out, the entire construction would come crashing down.
Therefore, they made it heresy (a crime against the teachings of the church) to
say that the sun was in the middle of the solar system, and not the earth.
Eventually, of course, scientific discoveries would prove the earlier theory
wrong, but not without casualties.
Steps toward the TRUTH:
COPERNICUS (1473-1543) :
Because the findings of Copernicus’ text went against Church doctrine, his
publisher went behind Copernicus’ back to downplay his theory, putting a
special foreword in his book that caused most people to ignore the findings.
(Most ironic is that Copernicus made his discoveries while working for the
Church - he was trying to fix the calendar). In On The Revolutions of the
Heavenly Orbs, Copernicus offers a theory based on mathematical
demonstration, that the sun was at the center of the solar system and fixed
stars, and that the earth was one of the planets revolving in space around IT.
This suggestion of a heliocentric cosmological model (sun in the middle)
helped to fix one of the worst problems associated with the Polemic model: more
and more observations were being made about the movement of the celestial bodies
(anything up in the sky) and more and more details weren’t being accommodated
by the old model.
For example: retrograde
motion. You see this every day, either in your car or on the subway. When
two objects running parallel to each other match in speed, object B appears to
have no speed relative to object A. In other words, if you look out the car
window, you can see the next lane’s car’s hubcap STOP SPINNING. It looks –
for a moment – like the wheel isn’t moving at all. But then you speed ahead
and his wheel STARTS MOVING BACKWARDS! Of course, it is not really moving
backwards, but from your perspective it seems to be because your speed is
greater than his. Well, the same thing happens with planets. Today we know that
Mars and Earth have concentric (sharing the same center) orbits. We move in the
same direction around the sun, but at different speeds because our orbit is
shorter than Mars. Mars is visible with the naked eye, and you can easily track
its movement in the evening sky. If you do track the movement of Mars, you will
note that for a set number of days, Mars will appear to move ever so slightly
across the sky, but then for a few days will appear in the same place, and then
it will appear to move backwards. Of course, it isn’t REALLY moving
backwards, any more than the car on the highway is, but from our perspective
it APPEARS to be moving backwards. This makes sense to us only because we know
that Mars and Earth are both moving. Imagine trying to make sense out of the
hubcap that stops spinning in mid-turn if you think that you are standing on the
sidewalk! The ancients (and all the way up to Galileo) thought that the Earth
was in the MIDDLE and DIDN’T MOVE, so they couldn’t explain this retrograde
motion at all. They added loop-de-loops called epicycles on the
mapping charts, desperately trying to account for this odd planetary behavior.
This caused John Milton to describe the cosmos as "with centric and
concentric scribbled o'er/, cycle and epicycle, orb in orb." The
problem? The EARTH IS NOT IN THE MIDDLE!
But Copernicus removed
the sun from the category of planets. Now he could argue – rightly – that
each orb was its own center, and that in each orbit all the heavy things fell
toward that center. This new system also allowed him to figure the distance from
the sun of various planets, based on the time it took them to complete their
revolution around it.
TYCHO BRAHE (1546-1601):
never accepted Copernican theory but gained more info about positions and
movements of heavenly bodies. He took very detailed records of starry
observations that would help Kepler later...
(1571-1630): student of Brahe - accepted Copernicus' theory. Kepler discovered
that the planets' orbits around the sun were ellipses, not perfect circles.
Explained why some planets took a shorter time to make their circuit. All math:
the square of the time is proportional to the cube of the distance.
first person to train a telescope on the heavens (1609). He was thus the first
to realize that these "orbs" and "points of light" were
substantial objects. In "The Starry Messenger" he describes his
One of the problems
Galileo solved was how to explain how the earth could move and not leave its
moon behind. This was one of the biggest arguments against scientific acceptance
of the "moving earth" theory. In "The Starry Messenger,"
Galileo observes the moons of Jupiter, which he names the Medicean Stars
to honor Cosimo de Medici. He plots the movement of the moons and concludes that
they move along with the planet, which everyone agrees does move across the sky.
If Jupiter can move and not lose its many moons, then Earth should have no
problem keeping hold of our one Moon. Galileo also observed the moon through his
telescope (he didn’t invent the telescope, but he was the first to train it on
the heavens). He noticed that the moon, always thought to be perfectly spherical
and without blemish, was in fact pock-marked and much like earth in many ways
– it had mountains, valleys, rugged surface… and Galileo proved that it was
not a luminous object – it reflected light, not produced it, as
So why does Galileo get
in trouble with the Church?
1. He agrees with the
idea that the earth moves, instead of staying motionless in the center and
letting other things revolve around it (like the Church says)
2. He compares the moon
to the earth several times (the moon has mountains and valleys, or when he
refers to a particular spot on the surface as being "about the size of
Bohemia."). Church doctrine forbids any comparison between the dirty,
sullied earth and the pristine and perfect heavenly bodies.
3. He usually wrote in
Italian, not Latin, in order to reach the general populace. But Galileo wrote Sidereus
Nuntius ("The Starry Messenger")in Latin in order to inform the
scientific public of his observations and conclusions. The church feared the
dissemination of such knowledge.
Details of Galileo’s
Era: during the papacy
of Pope Urban VIII.
Date: June 22, 1633.
Place: Santa Maria Sopra
Minerva, Dominican convent in center of Rome (ironically, in a church originally
dedicated to Minerva, the goddess of wisdom.)
Cause: G's publication
of Dialogue on the Two Principal World Systems in which he has characters
argue the relative merits of Ptolemaic (Aristotelian) and Copernican
cosmologies. The character arguing the Ptolemaic system comes out looking
Galileo had made the debater of the Church philosophy look positively stupid in
his book, he claimed that in fact that it was that argument he was in agreement
with. This was not a smart move and insulted his inquisitors.
"vehemently suspected of heresy"; Dialogue to be banned.
Sentence: sort of
probation - must repeat the penitential psalms once a week for three years -
returned home to Florence within five months and eventually went blind and died
after nine years of house arrest. Galileo would eventually be absolved by the
Church - in 1992!
in 1636, Galileo writes
his famous letter to the Grand Duchess Christina, wherein he makes an eloquent
argument FOR Church doctrine. In his letter he suggests that Aquinas is
absolutely right - that both the scriptures AND science must come to the same
conclusions about the universe and God's plan. If the two do not seem to agree,
Galileo says, then the fault lies with those who have misinterpreted the
Scripture. Because everything has to add up in the end.
WHAT YOU NEED TO KNOW
ABOUT GALILEO FOR THE EXAMINATION:
Be able to explain in
(Ptolemaic) cosmological model
Copernican cosmological model
Possible essay: Why
exactly does Galileo get in trouble? Be able to distinguish between Christian
theology (as put forth by St. Thomas Aquinas) and Greek natural philosophy (as
put forth mostly by Aristotle). Are they really reconcilable? Irreconcilable?
Think about this. Can science and religion work together to unravel the
mysteries of the universe? This question cannot be answered "yes" or
"no" but I expect you to put some thought into it.
for a tour of the
Galileo Room of the History of Science in Florence (including a peek at
Galileo's middle finger from his right hand - no kidding), go to:
for a very
informative website on Galileo, including an elaborate timeline:
and for really cool
pictures of the solar system (with a small section on our man):
Take the Galileo
quiz (put out by a publishing house hawking a Galileo book for the
uninformed - warning! It's Hard!)
All Rights Reserved
send comments to: Janice Siegel (firstname.lastname@example.org)
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