In 1604 the Western world witnessed evidence of the unspeakable, evidence of the changing
nature of the cosmos. In the foot of Ophiuchus a new star had appeared, brighter even than
Jupiter, and it was visible for a full18 months, before fading away. The old ways proclaimed that
the heavens where immortal and unchanging, but here was direct evidence of nature
contradicting that. Today we know it as Kepler’s Star, we witness it as the remnants of a
supernova, but in those dark times it was an omen, and almost literally a metaphor of the death
of the Aristotelian view of the Universe that Europe had been clinging to for millennia. One man
who watched that new star with interest would devote much of his life to the pursuit of scientific
truth. In 1605 he delivered 3 lectures at Padua University, in which he argued that parallax
measurements proved that the new star was beyond the moon in length, and that therefore
change did occur in the heavens. I argue that Galileo’s Galilei’s decades long struggle with the
unchanging paradigm of the Ancients brought about the true spirit of the scientific revolution,
which we hold true to today, which is not to believe or assume, but to always question; the
transition from faith to science.
It is believed that Galileo had held at the minimum an interest in the Copernican hypothesis at
least as far back as the early 1590s. In 1595, he used ideas based on Copernican motions of
the earth to devise a hypothesis to explain the motion of the tides. He would later expand upon
this in his seminal Dialogue on the Two Chief World Systems. In 1597 he wrote to Kepler;
another man who would reshape the scientific world in his own way. Galileo wrote; “I have for
many years been a partisan of the Copernican view... I have collected many proofs, but I do not
publish them, because I am deterred by the fate of our teacher Copernicus who…was ridiculed
and condemned by countless people...” Galileo waited patiently for more than a decade for his
opportunity to further prove and test his beliefs, and in 1609 with the discovery of an instrument
that allowed "seeing faraway things as though nearby” he took it.
A Tool To Smash A Paradigm
In the spring of 1609 after a single night devoted to consideration of the laws of refraction,
Galileo had discovered how to create his own telescope, constructing a triple magnification
spyglass from lenses he purchased in spectacle makers' shops. Whilst others had done the
same thing; what set Galileo apart was his excellent experimental skill, born of years of scientific
experience, and working with different lenses, he realized that, high magnification required a
weak convex lens and a strong concave lens. His problem was that opticians only made glasses
in a narrow range of strengths, and three or so was the best magnification available with these
off the shelf lenses. So, once again he applied his focus to learning another skill, and taught
himself the art of lens grinding. In applying his custom ground lenses, he discovered a way to
improve the instrument’s magnification, producing increasingly powerful telescopes over a
matter of months. By August he had presented an eight-powered instrument to the Venetian
Senate and by October he had constructed a telescope of twenty times magnification.
By 1610 Galileo was realizing the wondrous possibilities of this new scientific tool he had
refined, and using it to discover further evidence that demolished Aristotle’s now tenuous
paradigm. As well as possessing the most powerful telescope in the world, he was the first
person to do what now appears its most obvious use, and turn it to the stars. What he saw there
supported Copernicus’ hypotheses beyond the shadow of a doubt, and also made him a
dangerous threat to those who took the beliefs of the ancients, or the Bible to be dogma.
In November 1609 Galileo pointed his improved telescope towards the moon for the first time.
From November 30th until December 18th of that year, he examined and drew the face of the
moon in great detail. He found that the Moon was not the perfect unperturbed sphere that
Aristotle would have supported, a closer look at the surface revealed that, “the spots all have a
dark part on the side toward the Sun while on the side opposite the Sun they are crowned with
brighter borders like shining ridges." (Starry Messenger, p 41)
From these observations, Galileo deduced that he was observing the shadows cast by an
uneven surface, consisting of valleys, plains and mountains much like the surface of the Earth.
This conclusion was revelation, how could a heavenly body have an imperfect surface? Could it
be that the earth was also a heavenly body as well? Where was heaven and what was the
extent of the spread of the earthly corruption? Although this was not evidence directly
supporting the Copernican heliocentric theory, it challenged the Aristotelian and set the theme
for a number of more important discoveries that would support Copernicus.
Two months later, on January the 7th Galileo made the discovery of three of Jupiter's four largest
satellites; Io, Europa, and Callisto. On the 10th Galileo observed that one of them had
disappeared, which he attributed to it moving behind Jupiter. 3 days later he discovered
Ganymede, the last of what are now known as the Galilean moons. This discovery of satellites
orbiting Jupiter directly supported the Copernican hypothesis, which stated that “There is no
one center of all the celestial circles or spheres”. Firstly, it was contrary to the orderly geocentric
model of the universe, in which all celestial bodies circled around the Earth. This argument
suggested that given the moon orbited the Earth, if the Earth then orbited the Sun, the Moon
would be left behind. Moons orbiting around Jupiter implied that a planet could orbit another
body without leaving behind any moons that were in turn orbiting it. Secondly it was the
discovery of new bodies in the universe that according to the old theories simply shouldn’t
have been there, the crystalline sphere that Jupiter traversed across should have been
shattered by these new interfering bodies. Naturally, this was all a bit too much too soon, and
many prominent academics simply didn’t believe him, but his continued observations of the
moons meant that by mid 1611, he was able to accurately predict where each moon would be,
and all the unbelievers had to do was stare down the telescope (and many refused to)1…
In February Galileo also made some star maps, including the Pleiades. Although not of much
significance compared with what he was about to unearth, the discovery of more stars in the
heavens than where previously known suggested an infinite universe, lending support to an
ancient Greek argument against Aristotle on the plurality of worlds, first proposed by the
However, verifying Galileo's discoveries was initially difficult for anyone without access to
Galileo's uniquely powerful telescope, and in the spring of 1610 no one else had the capability
to observe the satellites of Jupiter. It would be about six months before others had access to
instruments powerful enough to see Jupiter's moons, and by then Galileo was already working
on the next big thing…
Galileo complains to Kepler in a letter dated 19th August 1610 of philosophers who “refuse to look” (Baumgardt,
In September of 1610, Galileo turned his telescope upon Venus. He noticed that it exhibited a
full set of phases, similar to that of the Moon. Ptolemy’s geocentric hypothesis predicted that
only crescent and new phases could be observed, Venus was supposed to remain between the
Sun and Earth during its orbit around the Earth. However, Copernicus’ heliocentric model
predicted that all phases would be visible since the orbit of Venus around the Sun would cause
its illuminated hemisphere to face the Earth when it was on the opposite side of the Sun and for
it to face away from the Earth when it was in between the sun and earth. Galileo's observations
of the phases of Venus proved that it orbited the Sun, and this effectively falsified the Ptolemaic
system beyond any shadow of doubt.
In March of 1610 Galileo hurriedly published his brief treatise, The Starry Messenger. It
explained the new discoveries that he had made with his telescope: the shape of the moon’s
surface, satellites orbiting Jupiter, and the resolution of what nebulae into collections of stars too
faint to see individually. Most importantly, for the first time he publically declared that the
planets moved around the sun. (Machamer, 1998). In 1613 Galileo began to tutor students on
the Copernican theory.
In April of 1612 the searching gaze of Galileo’s telescope focused upon the face of the sun. In
1613 he published his Letters on Sunspots, in which began a great argument with the Jesuit
Astronomer Christoph Scheiner by disproving Scheiner’s hypothesis that sunspots where
actually planets revolving around the sun, as argued under the pseudonym Apelles in Three
Letters on Solar Spots. Galileo pointed out that by moving together, and moving slowly,
sunspots could not be planets. He also pointed out their irregular shapes how they formed and
disappeared at random. Lastly he mentioned the foreshortening of the spots as they
approached the edge of the solar disk. Most importantly on pages 27 to 36 Galileo also began
to formulate a geometrical argument for Copernicanism based on the motion of sunspots, but
never finished it. However he did write “I tell you that also, no less than the horned Venus
agrees admirably with the great Copernican system. Favorable winds are now blowing on that
system… (Cropper, 2001). The implications of Galileo’s work here not only prevented any
‘saving’ of the theory, but started one of many feuds that would be characteristic of his later
fame in life, and where the first insult to the Jesuit order he would make.
And yet it moves...
As with countless other times in history, new and radically different ideas, no matter how
convincing, cannot simply be accepted without some level of resistance. Galileo was a proud
man, driven to defend his Copernican position against anyone who would argue with him, or to
uncompromisingly criticize anyone whom he disagreed with. At the beginning of the paradigm
shift, there was an abundance of people for him to criticize, argue and disagree with, and a
worldview to change.
In tandem with his growing notoriety, scattered resistance to Galileo began to come from all
over Europe. In June of 1610, a young Lutheran student of Kepler’s, Martin Horky, published A
very short excursion against the Sidereal Messenger. Interestingly it was more of a character
assassination upon Galileo himself, rather than Copernicus, claiming Galileo had invented the
Jovian moons due to a “thirst for gold”, and other slanderous character attacks. (Reston, 2000)
The next ineffective dig, this time upon Copernicanism, came from Francesco Sizzi, a Florentine
astronomer. In Dianoia Astronomica, Optica, Physica, he argued partly from scripture and partly
from mathematics. In part of his illogical argument Sizzi claimed; ”the satellites are invisible to
the naked eye and therefore can have no influence on the earth, and therefore would be
useless, and therefore do not exist”.
These and other small criticisms where no match for the amount of prestige Galileo was now
enjoying and number of influential friends he had made in his public life.
The first organized resistance came from a group, which Galileo contemptibly referred to as the
"Pigeon League" named after Lodovico delle Colombe, an Aristotelian professor of philosophy.
In 1611 Lodovico published a tract that really muddied the waters in the connection between
Christianity and the Aristotelians, Against the Motion of the Earth. Although it did not implicate
Galileo directly it argued against Copernicus from scripture. Initially the League was comprised
of Aristotelian scholars whom he had offended in public debates with his sarcastic and brutal
style of argument, such as Cesare Cremonini, who refused to look down his telescope! Later it
expanded to allow anyone with a grudge against Galileo in it. It is believed that this league is
responsible for creating the real trouble for Galileo, its members where those who brought his
argument on the passage Joshua 10: 22-24 to the attention of the Catholic Church, a far more
The Catholic Church had a lot invested in the belief system it enforced and was built upon, the
scripture was seen as simply correct and anything that threatened to disprove it was dangerous.
Copernicus’ belief in a moving earth contradicted the scripture, for example in Psalm 104:5 the
Bible states; "…the LORD set the earth on its foundations; it can never be moved." If Galileo
could prove Copernicus right, he would also disprove the infallibility of the Bible. Seeing as the
word of God was supposed to be perfect, the Catholic Church had everything to lose here. The
Church was an incredibly powerful force at the time, both in its grip on thinking, and on what it
could do in its self appointed position. Galileo just didn’t face resistance from the most powerful
organization of the era, but from an entire deeply entrenched philosophy and belief system that
had endured for over fifteen centuries, if he wanted to a challenging foe to disagree with, this
was undoubtedly it.
In December of 1613, after a debate in which a former student of Galileo’s, Benedetto Castelli
defended the Copernican system, Galileo wrote a letter congratulating Benedetto and in which
he stated that it was a mistake to interpret passages from scripture literally. He later expanded
this letter, and addressed it to the Grand Duchess Christine, a defender of scripture and one of
his powerful patrons mentioning "I hold that the Sun is located at the centre of the revolutions of
the heavenly orbs…” This could have been a step too far. These words would later be used
against him in his trial by the Inquisition.
The first attack on Galileo from the pulpit came in December 1614, from a young Dominican
priest named Tommaso Caccini, also a member of the ‘pigeon league’. Tommaso delivered a
furious sermon on the miracle of Joshua, and preached that it was heresy to support
Copernicanism as it violated scripture. Later, in 1615 another Dominican (and pigeon), Niccolo
Lorini, filed a written complaint to the Inquisition regarding Galileo's support of Copernican
views. As proof he enclosed a copy of Galileo's letter to Benedetto Castelli. A few weeks later,
on March 19th, Caccini traveled to the Inquisition's offices in Rome to denounce Galileo’s
Copernicanism and various other alleged heresies supposedly being spread by his (growing
number of) supporters.
In spite of this negative attention from members of the church, in 1616 Galileo wrote up a
treatise addressed to Cardinal Alessandro Orsini in which he claimed proved the earth moves.
He argued that the sloshing of the tides was caused by a rotation of the earth, building on his
previous tidal works. This was another overt piece of support for Copernicanism (“The earth…
performs a complete rotation on its fixed poles in a daily motion”). This did nothing to improve
his growing problem with the church.
In 1616 the Church decided to take the Tychonic model of the Universe, as a way to reconcile
the phases of Venus with literal interpretation of scripture. In this system, all the planets orbited
the Sun, which itself orbited the earth. Despite Tycho’s attempts to engage Galileo in debate
regarding this system, Galileo in an unusually non-conflictive way, did not even consider it
serious enough to mention in his next work The Dialogue...
Prelude To The Trial
One month after goading the church with his new tidal thesis, a Vatican commission decided
that the tenets of Copernicanism where “foolish and absurd and formally heretical”. On
February 25, 1616, the Inquisition met and received instructions from Pope Paul to direct
Galileo not to teach or defend or discuss Copernican doctrine.
The day after, on orders of the Pope Paul V, Cardinal Bellarmine called Galileo to his residence
and administered a warning; not to “hold or defend the Copernican theory”. Later, in March the
Church also suspended the distribution of Copernicus’ book De Revolutionibus until further
Although now prevented from supporting Copernicanism directly, Galileo continued his attack
upon Aristotelian philosophy in 1623 with the publishing of The Assayer. This book was direct
criticism of a treatise on the comets of 1618 by Orazio Grassi, a Jesuit mathematician of high
regard. Galileo argued that the comets where actually optical illusions, and in this case was
wrong. This was the second time he had criticized the Jesuits, and further strained his
relationship with the Catholic Church.
In 1632, the world had changed. Cardinal Bellarmine was now Pope Urban VIII and Galileo had
just published The Dialogue. Urban had requested that Galileo write a book which presented
balanced arguments for Heliocentrism. But through the foolish character of Simplicio, Galileo
really had taken it too far this time. Simplicio used Urban’s favorite argument that God could
produce any effect He wanted, so if He wanted to make a fixed Earth appear as if moving, then
it was an entirely possible explanation. The book was unmistakably biased in favour of the
Copernican system, violating Galileo’s warning from 1616 not to defend Copernicus, and more
importantly it offended the Pope. Furiously, Urban recalled Galileo to Rome to answer against
charges of Heresy!
This resulted in infamous trial of Galileo in 1633, in which he was forced to publically recant his
beliefs, and sentenced to spend the rest of his life confined to house-arrest in the home of the
archbishop of Siena. He continued to pursue science until his death at Arcetri, Florence in
Three centuries later, Galileo was officially ‘pardoned’ by Pope John Paul II.
Nobody knows if Galileo really knew the long term implications of what his work with the
telescope was going to achieve, what we do know is that he was driven by ambition and the
need for fame as much as anything. Headstrong, egotistical and argumentative, “The Father Of
Science” is hardly a shining example of the natural philosopher out to defend progress against
the backwards ravages of religious intolerance, but this essentially is what he was. It was these
qualities that he needed to overcome the fierce resistance his radical arguments faced,
especially from such powerful foes as the Church, and it was his creative use of the telescope
that proved Copernicus’ theory beyond any shadow of a doubt. If timid Copernicus was the one
who started the ball moving in the Copernican Revolution, then it was audacious Galileo who
took that ball and kicked it into the face of the old world system. Once truth had prevailed over
belief in astronomy, the seeds where planted for the blossoming of science in Europe. If the
scripture was wrong, what could the church rest on now? Decades later, Newton would
formulate his first law of motion based on Galileo’s theory of inertia, and it’s hard for anyone to
deny that the world would not be a different place if it had not been for Galileo Galilei.
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Reston, J. (2000). Galileo: A Life. Beard Books.