Galileo Galilei (Italian: [ɡaliˈlɛːo ɡaliˈlɛi]; 15
February 1564 – 8 January 1642) was an Italian polymath.
Galileo is a central figure in the transition from natural philosophy
to modern science and in the transformation of the scientific
Renaissance into a scientific revolution.
Galileo's championing of heliocentrism and Copernicanism was
controversial during his lifetime, when most subscribed to either
geocentrism or the Tychonic system. He met with opposition from
astronomers, who doubted heliocentrism because of the absence of an
observed stellar parallax. The matter was investigated by the Roman
Inquisition in 1615, which concluded that heliocentrism was "foolish
and absurd in philosophy, and formally heretical since it explicitly
contradicts in many places the sense of Holy Scripture."
Galileo later defended his views in Dialogue Concerning the Two Chief
World Systems (1632), which appeared to attack
Pope Urban VIII
Pope Urban VIII and
thus alienated him and the Jesuits, who had both supported Galileo up
until this point. He was tried by the Inquisition, found
"vehemently suspect of heresy", and forced to recant. He spent the
rest of his life under house arrest. While under house arrest,
he wrote one of his best-known works, Two New Sciences, in which he
summarized work he had done some forty years earlier on the two
sciences now called kinematics and strength of materials.
Galileo studied speed and velocity, gravity and free fall, the
principle of relativity, inertia, projectile motion and also worked in
applied science and technology, describing the properties of pendulums
and "hydrostatic balances", inventing the thermoscope and various
military compasses, and using the telescope for scientific
observations of celestial objects. His contributions to observational
astronomy include the telescopic confirmation of the phases of Venus,
the discovery of the four largest satellites of Jupiter, the
Saturn's rings (though he could not see them well
enough to discern their true nature) and the analysis of sunspots.
Known for his work as astronomer, physicist, engineer, philosopher,
and mathematician, Galileo has been called the "father of
observational astronomy", the "father of modern physics",
the "father of the scientific method", and even the "father of
1 Early life and family
2 Career as a scientist
2.1 Galileo, Kepler and theories of tides
Controversy over comets and The Assayer
Controversy over heliocentrism
4 Scientific contributions
4.1 Scientific methods
4.2.1 Kepler's supernova
4.2.2 Jupiter's moons
4.2.3 Venus, Saturn, and Neptune
Milky Way and stars
4.4.1 Falling bodies
6.1 Later Church reassessments
6.2 Impact on modern science
6.3 In artistic and popular media
7.1 Published written works
8 See also
11 External links
11.1 By Galileo
11.2 On Galileo
11.2.2 Galileo and the Church
Early life and family
Galileo was born in
Pisa (then part of the Duchy of Florence), Italy,
on 15 February 1564, the first of six children of Vincenzo
Galilei, a famous lutenist, composer, and music theorist, and Giulia
(née Ammannati), who had married in 1562. Galileo became an
accomplished lutenist himself and would have learned early from his
father a scepticism for established authority, the value of
well-measured or quantified experimentation, an appreciation for a
periodic or musical measure of time or rhythm, as well as the results
expected from a combination of mathematics and experiment.
Three of Galileo's five siblings survived infancy. The youngest,
Michelangelo (or Michelagnolo), also became a noted lutenist and
composer although he contributed to financial burdens during Galileo's
young adulthood. Michelangelo was unable to contribute his fair share
of their father's promised dowries to their brothers-in-law, who would
later attempt to seek legal remedies for payments due. Michelangelo
would also occasionally have to borrow funds from Galileo to support
his musical endeavours and excursions. These financial burdens may
have contributed to Galileo's early desire to develop inventions that
would bring him additional income.
Galileo Galilei was eight, his family moved to Florence, but he
was left with Jacopo Borghini for two years. He then was educated in
the Vallombrosa Abbey, about 30 km southeast of Florence.
The surname Galilei derives from the given name of an ancestor,
Galileo Bonaiuti, a physician, university teacher and politician who
Florence from 1370 to 1450; his descendents had changed their
family name from Bonaiuti (or Buonaiuti) to Galilei in his honor in
the late 14th century. Galileo Bonaiuti was buried in the same
church, the Basilica of Santa Croce in Florence, where about 200 years
later his more famous descendant
Galileo Galilei was also
It was common for mid-sixteenth century Tuscan families to name the
eldest son after the parents' surname. Hence,
Galileo Galilei was
not necessarily named after his ancestor Galileo Bonaiuti. The Italian
male given name "Galileo" (and thence the surname "Galilei") derives
from the Latin "Galilaeus", meaning "of Galilee", a biblically
significant region in Northern Israel.
The biblical roots of Galileo's name and surname were to become the
subject of a famous pun. In 1614, during the Galileo affair, one
of Galileo's opponents, the Dominican priest Tommaso Caccini,
delivered against Galileo a controversial and influential sermon. In
it he made a point of quoting Acts 1:11, "Ye men of Galilee, why stand
ye gazing up into heaven?".
Galileo's beloved elder daughter, Virginia (Sister Maria Celeste), was
particularly devoted to her father. She is buried with him in his tomb
in the Basilica of Santa Croce, Florence.
Despite being a genuinely pious Roman Catholic, Galileo fathered
three children out of wedlock with Marina Gamba. They had two
daughters, Virginia (born in 1600) and Livia (born in 1601), and a
son, Vincenzo (born in 1606).
Because of their illegitimate birth, their father considered the girls
unmarriageable, if not posing problems of prohibitively expensive
support or dowries, which would have been similar to Galileo's
previous extensive financial problems with two of his sisters.
Their only worthy alternative was the religious life. Both girls were
accepted by the convent of San Matteo in
Arcetri and remained there
for the rest of their lives. Virginia took the name Maria Celeste
upon entering the convent. She died on 2 April 1634, and is buried
with Galileo at the Basilica of Santa Croce, Florence. Livia took the
name Sister Arcangela and was ill for most of her life. Vincenzo was
later legitimised as the legal heir of Galileo and married Sestilia
Career as a scientist
Although Galileo seriously considered the priesthood as a young man,
at his father's urging he instead enrolled at the University of Pisa
for a medical degree. In 1581, when he was studying medicine, he
noticed a swinging chandelier, which air currents shifted about to
swing in larger and smaller arcs. To him, it seemed, by comparison
with his heartbeat, that the chandelier took the same amount of time
to swing back and forth, no matter how far it was swinging. When he
returned home, he set up two pendulums of equal length and swung one
with a large sweep and the other with a small sweep and found that
they kept time together. It was not until the work of Christiaan
Huygens, almost one hundred years later, that the tautochrone nature
of a swinging pendulum was used to create an accurate timepiece.
Up to this point, Galileo had deliberately been kept away from
mathematics, since a physician earned a higher income than a
mathematician. However, after accidentally attending a lecture on
geometry, he talked his reluctant father into letting him study
mathematics and natural philosophy instead of medicine. He created
a thermoscope, a forerunner of the thermometer, and, in 1586,
published a small book on the design of a hydrostatic balance he had
invented (which first brought him to the attention of the scholarly
world). Galileo also studied disegno, a term encompassing fine art,
and, in 1588, obtained the position of instructor in the Accademia
delle Arti del Disegno in Florence, teaching perspective and
chiaroscuro. Being inspired by the artistic tradition of the city and
the works of the Renaissance artists, Galileo acquired an aesthetic
mentality. While a young teacher at the Accademia, he began a lifelong
friendship with the Florentine painter Cigoli, who included Galileo's
lunar observations in one of his paintings.
In 1589, he was appointed to the chair of mathematics in Pisa. In
1591, his father died, and he was entrusted with the care of his
younger brother Michelagnolo. In 1592, he moved to the University of
Padua where he taught geometry, mechanics, and astronomy until
1610. During this period, Galileo made significant discoveries in
both pure fundamental science (for example, kinematics of motion and
astronomy) as well as practical applied science (for example, strength
of materials and pioneering the telescope). His multiple interests
included the study of astrology, which at the time was a discipline
tied to the studies of mathematics and astronomy.
Galileo, Kepler and theories of tides
Galileo Galilei. Portrait by Leoni
Cardinal Bellarmine had written in 1615 that the Copernican system
could not be defended without "a true physical demonstration that the
sun does not circle the earth but the earth circles the sun".
Galileo considered his theory of the tides to provide the required
physical proof of the motion of the earth. This theory was so
important to him that he originally intended to entitle his Dialogue
on the Two Chief World Systems the Dialogue on the Ebb and Flow of the
Sea. The reference to tides was removed from the title by order of
For Galileo, the tides were caused by the sloshing back and forth of
water in the seas as a point on the Earth's surface sped up and slowed
down because of the Earth's rotation on its axis and revolution around
the Sun. He circulated his first account of the tides in 1616,
addressed to Cardinal Orsini. His theory gave the first insight
into the importance of the shapes of ocean basins in the size and
timing of tides; he correctly accounted, for instance, for the
negligible tides halfway along the
Adriatic Sea compared to those at
the ends. As a general account of the cause of tides, however, his
theory was a failure.
If this theory were correct, there would be only one high tide per
day. Galileo and his contemporaries were aware of this inadequacy
because there are two daily high tides at
Venice instead of one, about
twelve hours apart. Galileo dismissed this anomaly as the result of
several secondary causes including the shape of the sea, its depth,
and other factors. Against the assertion that Galileo was
deceptive in making these arguments,
Albert Einstein expressed the
opinion that Galileo developed his "fascinating arguments" and
accepted them uncritically out of a desire for physical proof of the
motion of the Earth. Galileo dismissed the idea, held by his
contemporary Johannes Kepler, that the moon caused the tides.
(Galileo also took no interest in Kepler's elliptical orbits of the
Controversy over comets and The Assayer
Main article: The Assayer
In 1619, Galileo became embroiled in a controversy with Father Orazio
Grassi, professor of mathematics at the
Jesuit Collegio Romano. It
began as a dispute over the nature of comets, but by the time Galileo
The Assayer (Il Saggiatore) in 1623, his last salvo in
the dispute, it had become a much wider controversy over the very
nature of science itself. The title page of the book describes Galileo
as philosopher and "Matematico Primario" of the Grand Duke of Tuscany.
The Assayer contains such a wealth of Galileo's ideas on how
science should be practised, it has been referred to as his scientific
manifesto. Early in 1619, Father Grassi had anonymously published
a pamphlet, An Astronomical Disputation on the Three Comets of the
Year 1618, which discussed the nature of a comet that had appeared
late in November of the previous year. Grassi concluded that the comet
was a fiery body which had moved along a segment of a great circle at
a constant distance from the earth, and since it moved in the sky
more slowly than the moon, it must be farther away than the moon.
Grassi's arguments and conclusions were criticised in a subsequent
article, Discourse on Comets, published under the name of one of
Galileo's disciples, a Florentine lawyer named Mario Guiducci,
although it had been largely written by Galileo himself. Galileo
and Guiducci offered no definitive theory of their own on the nature
of comets although they did present some tentative conjectures
that are now known to be mistaken. In its opening passage, Galileo and
Guiducci's Discourse gratuitously insulted the
Scheiner, and various uncomplimentary remarks about the professors
Collegio Romano were scattered throughout the work. The
Jesuits were offended, and Grassi soon replied with a polemical
tract of his own, The Astronomical and Philosophical Balance,
under the pseudonym Lothario Sarsio Sigensano, purporting to be
one of his own pupils.
The Assayer was Galileo's devastating reply to the Astronomical
Balance. It has been widely recognized as a masterpiece of
polemical literature, in which "Sarsi's" arguments are subjected
to withering scorn. It was greeted with wide acclaim, and
particularly pleased the new pope, Urban VIII, to whom it had been
dedicated. In Rome, in the previous decade, Barberini, the future
Urban VIII, had come down on the side of Galileo and the Lincean
Galileo's dispute with Grassi permanently alienated many of the
Jesuits who had previously been sympathetic to his ideas, and
Galileo and his friends were convinced that these
responsible for bringing about his later condemnation. The
evidence for this is at best equivocal, however.
Controversy over heliocentrism
Main article: Galileo affair
Cristiano Banti's 1857 painting Galileo facing the Roman Inquisition
In the Christian world prior to Galileo's conflict with the Church,
the majority of educated people subscribed either to the Aristotelian
geocentric view that the earth was the center of the universe and that
all heavenly bodies revolved around the Earth, or the Tychonic
system that blended geocentrism with heliocentrism. Nevertheless,
following the death of Copernicus and before Galileo, heliocentrism
was relatively uncontroversial; Copernicus's work was used by Pope
Gregory XIII to reform the calendar in 1582.
Opposition to heliocentrism and Galileo's writings combined religious
and scientific objections and were fueled by political events.
Scientific opposition came from
Tycho Brahe and others and arose from
the fact that, if heliocentrism were true, an annual stellar parallax
should be observed, though none was. Copernicus had correctly
postulated that parallax was negligible because the stars were so
distant. However, Brahe had countered that, since stars appeared to
have measurable size, if the stars were that distant, they would be
gigantic, and in fact far larger than the
Sun or any other celestial
body. In Brahe's system, by contrast, the stars were a little more
distant than Saturn, and the
Sun and stars were comparable in
Religious opposition to heliocentrism arose from Biblical references
such as Psalm 93:1, 96:10, and 1 Chronicles 16:30 which include text
stating that "the world is firmly established, it cannot be moved." In
the same manner, Psalm 104:5 says, "the Lord set the earth on its
foundations; it can never be moved." Further,
Ecclesiastes 1:5 states
that "And the sun rises and sets and returns to its place."
Galileo defended heliocentrism based on his astronomical observations
of 1609 (
Sidereus Nuncius 1610). In December 1613, the Grand Duchess
Florence confronted one of Galileo's friends and
followers, Benedetto Castelli, with biblical objections to the motion
of the earth. According to Maurice Finocchiaro, this was done in a
friendly and gracious manner, out of curiosity. Prompted by this
incident, Galileo wrote a letter to Castelli in which he argued that
heliocentrism was actually not contrary to biblical texts, and that
the bible was an authority on faith and morals, not on science. This
letter was not published, but circulated widely.
By 1615, Galileo's writings on heliocentrism had been submitted to the
Roman Inquisition by Father Niccolo Lorini, who claimed that Galileo
and his followers were attempting to reinterpret the Bible, which was
seen as a violation of the
Council of Trent
Council of Trent and looked dangerously
like Protestantism. Lorini specifically cited Galileo's letter to
Castelli. Galileo went to Rome to defend himself and his
Copernican and biblical ideas. At the start of 1616, Monsignor
Francesco Ingoli initiated a debate with Galileo, sending him an essay
disputing the Copernican system. Galileo later stated that he believed
this essay to have been instrumental in the action against
Copernicanism that followed. According to Maurice Finocchiaro,
Ingoli had probably been commissioned by the
Inquisition to write an
expert opinion on the controversy, and the essay provided the "chief
direct basis" for the Inquisition's actions. The essay focused on
eighteen physical and mathematical arguments against heliocentrism. It
borrowed primarily from the arguments of Tycho Brahe, and it notedly
mentioned Brahe's argument that heliocentrism required the stars to be
much larger than the Sun. Ingoli wrote that the great distance to the
stars in the heliocentric theory "clearly proves ... the fixed stars
to be of such size, as they may surpass or equal the size of the orbit
circle of the
Earth itself." The essay also included four
theological arguments, but Ingoli suggested Galileo focus on the
physical and mathematical arguments, and he did not mention Galileo's
biblical ideas. In February 1616, an Inquisitorial commission
declared heliocentrism to be "foolish and absurd in philosophy, and
formally heretical since it explicitly contradicts in many places the
sense of Holy Scripture." The
Inquisition found that the idea of the
Earth's movement "receives the same judgement in philosophy and... in
regard to theological truth it is at least erroneous in faith".
(The original document from the Inquisitorial commission was made
widely available in 2014.)
Pope Paul V
Pope Paul V instructed Cardinal Bellarmine to deliver this finding to
Galileo, and to order him to abandon the opinion that heliocentrism
was physically true. On 26 February, Galileo was called to
Bellarmine's residence and ordered:
... to abandon completely... the opinion that the sun stands still at
the center of the world and the earth moves, and henceforth not to
hold, teach, or defend it in any way whatever, either orally or in
The decree of the
Congregation of the Index
Congregation of the Index banned Copernicus's De
Revolutionibus and other heliocentric works until correction.
Bellarmine's instructions did not prohibit Galileo from discussing
heliocentrism as a mathematical and philosophic idea, so long as he
did not advocate for its physical truth.
For the next decade, Galileo stayed well away from the controversy. He
revived his project of writing a book on the subject, encouraged by
the election of Cardinal Maffeo
Pope Urban VIII
Pope Urban VIII in 1623.
Barberini was a friend and admirer of Galileo, and had opposed the
condemnation of Galileo in 1616. Galileo's resulting book, Dialogue
Concerning the Two Chief World Systems, was published in 1632, with
formal authorization from the
Inquisition and papal permission.
Pope Urban VIII
Pope Urban VIII had personally asked Galileo to give
arguments for and against heliocentrism in the book, and to be careful
not to advocate heliocentrism. He made another request, that his own
views on the matter be included in Galileo's book. Only the latter of
those requests was fulfilled by Galileo.
Whether unknowingly or deliberately, Simplicio, the defender of the
Aristotelian geocentric view in Dialogue Concerning the Two Chief
World Systems, was often caught in his own errors and sometimes came
across as a fool. Indeed, although Galileo states in the preface of
his book that the character is named after a famous Aristotelian
philosopher (Simplicius in Latin, "Simplicio" in Italian), the name
"Simplicio" in Italian also has the connotation of "simpleton".
This portrayal of Simplicio made Dialogue Concerning the Two Chief
World Systems appear as an advocacy book: an attack on Aristotelian
geocentrism and defence of the Copernican theory. Unfortunately for
his relationship with the Pope, Galileo put the words of Urban VIII
into the mouth of Simplicio.
Most historians agree Galileo did not act out of malice and felt
blindsided by the reaction to his book. However, the Pope did not
take the suspected public ridicule lightly, nor the Copernican
Galileo had alienated one of his biggest and most powerful supporters,
the Pope, and was called to Rome to defend his writings in
September 1632. He finally arrived in February 1633 and was brought
Vincenzo Maculani to be charged. Throughout his
trial, Galileo steadfastly maintained that since 1616 he had
faithfully kept his promise not to hold any of the condemned opinions,
and initially he denied even defending them. However, he was
eventually persuaded to admit that, contrary to his true intention, a
reader of his Dialogue could well have obtained the impression that it
was intended to be a defence of Copernicanism. In view of Galileo's
rather implausible denial that he had ever held Copernican ideas after
1616 or ever intended to defend them in the Dialogue, his final
interrogation, in July 1633, concluded with his being threatened with
torture if he did not tell the truth, but he maintained his denial
despite the threat.
The sentence of the
Inquisition was delivered on 22 June. It was in
three essential parts:
Galileo was found "vehemently suspect of heresy", namely of having
held the opinions that the
Sun lies motionless at the centre of the
universe, that the
Earth is not at its centre and moves, and that one
may hold and defend an opinion as probable after it has been declared
contrary to Holy Scripture. He was required to "abjure, curse and
detest" those opinions.
He was sentenced to formal imprisonment at the pleasure of the
Inquisition. On the following day, this was commuted to house
arrest, which he remained under for the rest of his life.
His offending Dialogue was banned; and in an action not announced at
the trial, publication of any of his works was forbidden, including
any he might write in the future.
Portrait, attributed to Murillo, of Galileo gazing at the words "E pur
si muove" (And yet it moves) (not legible in this image) scratched on
the wall of his prison cell
According to popular legend, after recanting his theory that the Earth
moved around the Sun, Galileo allegedly muttered the rebellious phrase
"And yet it moves". A 1640s painting by the Spanish painter Bartolomé
Esteban Murillo or an artist of his school, in which the words were
hidden until restoration work in 1911, depicts an imprisoned Galileo
apparently gazing at the words "E pur si muove" written on the wall of
his dungeon. The earliest known written account of the legend dates to
a century after his death, but
Stillman Drake writes "there is no
doubt now that the famous words were already attributed to Galileo
before his death".
After a period with the friendly Ascanio Piccolomini (the Archbishop
of Siena), Galileo was allowed to return to his villa at
Florence in 1634, where he spent the remainder of his life under house
arrest. Galileo was ordered to read the seven penitential psalms once
a week for the next three years. However, his daughter Maria Celeste
relieved him of the burden after securing ecclesiastical permission to
take it upon herself.
It was while Galileo was under house arrest that he dedicated his time
to one of his finest works, Two New Sciences. Here he summarised work
he had done some forty years earlier, on the two sciences now called
kinematics and strength of materials, published in Holland to avoid
the censor. This book has received high praise from Albert
Einstein. As a result of this work, Galileo is often called the
"father of modern physics". He went completely blind in 1638 and was
suffering from a painful hernia and insomnia, so he was permitted to
Florence for medical advice.
Dava Sobel argues that prior to Galileo's 1633 trial and judgement for
Pope Urban VIII
Pope Urban VIII had become preoccupied with court intrigue and
problems of state, and began to fear persecution or threats to his own
life. In this context, Sobel argues that the problem of Galileo was
presented to the pope by court insiders and enemies of Galileo. Having
been accused of weakness in defending the church, Urban reacted
against Galileo out of anger and fear.
Tomb of Galileo, Santa Croce, Florence
Galileo continued to receive visitors until 1642, when, after
suffering fever and heart palpitations, he died on 8 January 1642,
aged 77. The Grand Duke of Tuscany, Ferdinando II, wished to
bury him in the main body of the Basilica of Santa Croce, next to the
tombs of his father and other ancestors, and to erect a marble
mausoleum in his honour.
Middle finger of Galileo's right hand
These plans were dropped, however, after
Pope Urban VIII
Pope Urban VIII and his
nephew, Cardinal Francesco Barberini, protested, because Galileo
had been condemned by the
Catholic Church for "vehement suspicion of
heresy". He was instead buried in a small room next to the
novices' chapel at the end of a corridor from the southern transept of
the basilica to the sacristy. He was reburied in the main body of
the basilica in 1737 after a monument had been erected there in his
honour; during this move, three fingers and a tooth were removed
from his remains. One of these fingers, the middle finger from
Galileo's right hand, is currently on exhibition at the Museo Galileo
in Florence, Italy.
Galileo made original contributions to the science of motion through
an innovative combination of experiment and mathematics. More
typical of science at the time were the qualitative studies of William
Gilbert, on magnetism and electricity. Galileo's father, Vincenzo
Galilei, a lutenist and music theorist, had performed experiments
establishing perhaps the oldest known non-linear relation in physics:
for a stretched string, the pitch varies as the square root of the
tension. These observations lay within the framework of the
Pythagorean tradition of music, well-known to instrument makers, which
included the fact that subdividing a string by a whole number produces
a harmonious scale. Thus, a limited amount of mathematics had long
related music and physical science, and young Galileo could see his
own father's observations expand on that tradition.
Galileo was one of the first modern thinkers to clearly state that the
laws of nature are mathematical. In The Assayer, he wrote "Philosophy
is written in this grand book, the universe ... It is written in
the language of mathematics, and its characters are triangles,
circles, and other geometric figures;...." His mathematical
analyses are a further development of a tradition employed by late
scholastic natural philosophers, which Galileo learned when he studied
philosophy. His work marked another step towards the eventual
separation of science from both philosophy and religion; a major
development in human thought. He was often willing to change his views
in accordance with observation. In order to perform his experiments,
Galileo had to set up standards of length and time, so that
measurements made on different days and in different laboratories
could be compared in a reproducible fashion. This provided a reliable
foundation on which to confirm mathematical laws using inductive
Galileo showed a modern appreciation for the proper relationship
between mathematics, theoretical physics, and experimental physics. He
understood the parabola, both in terms of conic sections and in terms
of the ordinate (y) varying as the square of the abscissa (x). Galilei
further asserted that the parabola was the theoretically ideal
trajectory of a uniformly accelerated projectile in the absence of air
resistance or other disturbances. He conceded that there are limits to
the validity of this theory, noting on theoretical grounds that a
projectile trajectory of a size comparable to that of the
not possibly be a parabola, but he nevertheless maintained that
for distances up to the range of the artillery of his day, the
deviation of a projectile's trajectory from a parabola would be only
Galileo showed the Doge of
Venice how to use the telescope (Fresco by
It was on this page that Galileo first noted an observation of the
moons of Jupiter. This observation upset the notion that all celestial
bodies must revolve around the Earth. Galileo published a full
Sidereus Nuncius in March 1610
The phases of Venus, observed by Galileo in 1610
Based only on uncertain descriptions of the first practical telescope
Hans Lippershey tried to patent in the Netherlands in 1608,
Galileo, in the following year, made a telescope with about 3x
magnification. He later made improved versions with up to about 30x
magnification. With a Galilean telescope, the observer could see
magnified, upright images on the earth—it was what is commonly known
as a terrestrial telescope or a spyglass. He could also use it to
observe the sky; for a time he was one of those who could construct
telescopes good enough for that purpose. On 25 August 1609, he
demonstrated one of his early telescopes, with a magnification of
about 8 or 9, to Venetian lawmakers. His telescopes were also a
profitable sideline for Galileo, who sold them to merchants who found
them useful both at sea and as items of trade. He published his
initial telescopic astronomical observations in March 1610 in a brief
Sidereus Nuncius (Starry Messenger).
Tycho and others had observed the supernova of 1572. Ottavio
Brenzoni's letter of 15 January 1605 to Galileo brought the 1572
supernova and the less bright nova of 1601 to Galileo's notice.
Galileo observed and discussed Kepler's supernova in 1604. Since these
new stars displayed no detectable diurnal parallax, Galileo concluded
that they were distant stars, and, therefore, disproved the
Aristotelian belief in the immutability of the heavens.
On 7 January 1610, Galileo observed with his telescope what he
described at the time as "three fixed stars, totally invisible by
their smallness", all close to Jupiter, and lying on a straight line
through it. Observations on subsequent nights showed that the
positions of these "stars" relative to
Jupiter were changing in a way
that would have been inexplicable if they had really been fixed stars.
On 10 January, Galileo noted that one of them had disappeared, an
observation which he attributed to its being hidden behind Jupiter.
Within a few days, he concluded that they were orbiting Jupiter:
he had discovered three of Jupiter's four largest moons. He discovered
the fourth on 13 January. Galileo named the group of four the Medicean
stars, in honour of his future patron, Cosimo II de' Medici, Grand
Duke of Tuscany, and Cosimo's three brothers. Later astronomers,
however, renamed them Galilean satellites in honour of their
discoverer. These satellites are now called Io, Europa, Ganymede, and
His observations of the satellites of
Jupiter caused a revolution in
astronomy: a planet with smaller planets orbiting it did not conform
to the principles of Aristotelian cosmology, which held that all
heavenly bodies should circle the Earth, and many astronomers and
philosophers initially refused to believe that Galileo could have
discovered such a thing. His observations were confirmed by the
Christopher Clavius and he received a hero's welcome
when he visited Rome in 1611. Galileo continued to observe the
satellites over the next eighteen months, and by mid-1611, he had
obtained remarkably accurate estimates for their periods—a feat
which Kepler had believed impossible.
Venus, Saturn, and Neptune
From September 1610, Galileo observed that
Venus exhibited a full set
of phases similar to that of the Moon. The heliocentric model of the
solar system developed by
Nicolaus Copernicus predicted that all
phases would be visible since the orbit of
Venus around the
cause its illuminated hemisphere to face the
Earth when it was on the
opposite side of the
Sun and to face away from the
Earth when it was
on the Earth-side of the Sun. On the other hand, in Ptolemy's
geocentric model it was impossible for any of the planets' orbits to
intersect the spherical shell carrying the Sun. Traditionally, the
Venus was placed entirely on the near side of the Sun, where
it could exhibit only crescent and new phases. It was, however, also
possible to place it entirely on the far side of the Sun, where it
could exhibit only gibbous and full phases. After Galileo's telescopic
observations of the crescent, gibbous and full phases of Venus,
therefore, this Ptolemaic model became untenable. Thus in the early
17th century, as a result of his discovery, the great majority of
astronomers converted to one of the various geo-heliocentric planetary
models, such as the Tychonic, Capellan and Extended Capellan
models, each either with or without a daily rotating Earth. These
all had the virtue of explaining the phases of
Venus without the vice
of the 'refutation' of full heliocentrism's prediction of stellar
parallax. Galileo's discovery of the phases of
Venus was thus arguably
his most empirically practically influential contribution to the
two-stage transition from full geocentrism to full heliocentrism via
Galileo observed the planet Saturn, and at first mistook its rings for
planets, thinking it was a three-bodied system. When he observed the
Saturn's rings were directly oriented at Earth, causing
him to think that two of the bodies had disappeared. The rings
reappeared when he observed the planet in 1616, further confusing
Galileo also observed the planet
Neptune in 1612. It appears in his
notebooks as one of many unremarkable dim stars. He did not realise
that it was a planet, but he did note its motion relative to the stars
before losing track of it.
Galileo's "cannocchiali" telescopes at the Museo Galileo, Florence
Galileo made naked-eye and telescopic studies of sunspots. Their
existence raised another difficulty with the unchanging perfection of
the heavens as posited in orthodox Aristotelian celestial physics. An
apparent annual variation in their trajectories, observed by Francesco
Sizzi and others in 1612–1613, also provided a powerful
argument against both the Ptolemaic system and the geoheliocentric
system of Tycho Brahe. A dispute over claimed priority in the
discovery of sunspots, and in their interpretation, led Galileo to a
long and bitter feud with the
Jesuit Christoph Scheiner. In the middle
was Mark Welser, to whom Scheiner had announced his discovery, and who
asked Galileo for his opinion. In fact, there is
little doubt that both of them were beaten by
David Fabricius and his
Prior to Galileo's construction of his version of a telescope, Thomas
Harriot, an English mathematician and explorer, had already used what
he dubbed a "perspective tube" to observe the moon. Reporting his
observations, Harriot noted only "strange spottednesse" in the waning
of the crescent, but was ignorant to the cause. Galileo, due in part
to his artistic training and the knowledge of chiaroscuro, had
understood the patterns of light and shadow were, in fact,
topographical markers. While not being the only one to observe the
moon through a telescope, Galileo was the first to deduce the cause of
the uneven waning as light occlusion from lunar mountains and craters.
In his study, he also made topographical charts, estimating the
heights of the mountains. The moon was not what was long thought to
have been a translucent and perfect sphere, as
Aristotle claimed, and
hardly the first "planet", an "eternal pearl to magnificently ascend
into the heavenly empyrian", as put forth by Dante.
Milky Way and stars
Galileo observed the Milky Way, previously believed to be nebulous,
and found it to be a multitude of stars packed so densely that they
Earth to be clouds. He located many other stars too
distant to be visible with the naked eye. He observed the double star
Mizar in Ursa Major in 1617.
In the Starry Messenger, Galileo reported that stars appeared as mere
blazes of light, essentially unaltered in appearance by the telescope,
and contrasted them to planets, which the telescope revealed to be
discs. But shortly thereafter, in his Letters on Sunspots, he reported
that the telescope revealed the shapes of both stars and planets to be
"quite round". From that point forward, he continued to report that
telescopes showed the roundness of stars, and that stars seen through
the telescope measured a few seconds of arc in diameter. He also
devised a method for measuring the apparent size of a star without a
telescope. As described in his Dialogue Concerning the two Chief World
Systems, his method was to hang a thin rope in his line of sight to
the star and measure the maximum distance from which it would wholly
obscure the star. From his measurements of this distance and of the
width of the rope, he could calculate the angle subtended by the star
at his viewing point. In his Dialogue, he reported that he had
found the apparent diameter of a star of first magnitude to be no more
than 5 arcseconds, and that of one of sixth magnitude to be about 5/6
arcseconds. Like most astronomers of his day, Galileo did not
recognise that the apparent sizes of stars that he measured were
spurious, caused by diffraction and atmospheric distortion (see seeing
disk or Airy disk), and did not represent the true sizes of stars.
However, Galileo's values were much smaller than previous estimates of
the apparent sizes of the brightest stars, such as those made by Tycho
Brahe (see Magnitude) and enabled Galileo to counter anti-Copernican
arguments such as those made by Tycho that these stars would have to
be absurdly large for their annual parallaxes to be undetectable.
Other astronomers such as Simon Marius, Giovanni Battista Riccioli,
and Martinus Hortensius made similar measurements of stars, and Marius
and Riccioli concluded the smaller sizes were not small enough to
answer Tycho's argument.
Galileo's geometrical and military compass, thought to have been made
c. 1604 by his personal instrument-maker Marc'Antonio Mazzoleni
Galileo made a number of contributions to what is now known as
engineering, as distinct from pure physics. Between 1595 and 1598,
Galileo devised and improved a Geometric and military compass suitable
for use by gunners and surveyors. This expanded on earlier instruments
Niccolò Tartaglia and Guidobaldo del Monte. For gunners,
it offered, in addition to a new and safer way of elevating cannons
accurately, a way of quickly computing the charge of gunpowder for
cannonballs of different sizes and materials. As a geometric
instrument, it enabled the construction of any regular polygon,
computation of the area of any polygon or circular sector, and a
variety of other calculations. Under Galileo's direction, instrument
Marc'Antonio Mazzoleni produced more than 100 of these
compasses, which Galileo sold (along with an instruction manual he
wrote) for 50 lire and offered a course of instruction in the use of
the compasses for 120 lire.
In about 1593, Galileo constructed a thermometer, using the expansion
and contraction of air in a bulb to move water in an attached tube.
A replica of the earliest surviving telescope attributed to Galileo
Galilei, on display at the Griffith Observatory.
In 1609, Galileo was, along with Englishman
Thomas Harriot and others,
among the first to use a refracting telescope as an instrument to
observe stars, planets or moons. The name "telescope" was coined for
Galileo's instrument by a Greek mathematician, Giovanni
Demisiani, at a banquet held in 1611 by Prince
Federico Cesi to
make Galileo a member of his Accademia dei Lincei. The name was
derived from the Greek tele = 'far' and skopein = 'to look or see'. In
1610, he used a telescope at close range to magnify the parts of
insects. By 1624, Galileo had used a compound microscope. He
gave one of these instruments to Cardinal Zollern in May of that year
for presentation to the Duke of Bavaria, and in September, he
sent another to Prince Cesi. The Linceans played a role again in
naming the "microscope" a year later when fellow academy member
Giovanni Faber coined the word for Galileo's invention from the Greek
words μικρόν (micron) meaning "small", and σκοπεῖν
(skopein) meaning "to look at". The word was meant to be analogous
with "telescope". Illustrations of insects made using one of
Galileo's microscopes and published in 1625, appear to have been the
first clear documentation of the use of a compound microscope.
In 1612, having determined the orbital periods of Jupiter's
satellites, Galileo proposed that with sufficiently accurate knowledge
of their orbits, one could use their positions as a universal clock,
and this would make possible the determination of longitude. He worked
on this problem from time to time during the remainder of his life,
but the practical problems were severe. The method was first
successfully applied by
Giovanni Domenico Cassini
Giovanni Domenico Cassini in 1681 and was
later used extensively for large land surveys; this method, for
example, was used to survey France, and later by
Zebulon Pike of the
midwestern United States in 1806. For sea navigation, where delicate
telescopic observations were more difficult, the longitude problem
eventually required development of a practical portable marine
chronometer, such as that of John Harrison. Late in his life,
when totally blind, Galileo designed an escapement mechanism for a
pendulum clock (called Galileo's escapement), although no clock using
this was built until after the first fully operational pendulum clock
was made by
Christiaan Huygens in the 1650s.
Galileo was invited on several occasions to advise on engineering
schemes to alleviate river flooding. In 1630
Mario Guiducci was
probably instrumental in ensuring that he was consulted on a scheme by
Bartolotti to cut a new channel for the Bisenzio River near
Galileo e Viviani, 1892, Tito Lessi
Dome of the Cathedral of
Pisa with the "lamp of Galileo"
Galileo's theoretical and experimental work on the motions of bodies,
along with the largely independent work of Kepler and René Descartes,
was a precursor of the classical mechanics developed by Sir Isaac
Newton. Galileo conducted several experiments with pendulums. It is
popularly believed (thanks to the biography by Vincenzo Viviani) that
these began by watching the swings of the bronze chandelier in the
cathedral of Pisa, using his pulse as a timer. Later experiments are
described in his Two New Sciences. Galileo claimed that a simple
pendulum is isochronous, i.e. that its swings always take the same
amount of time, independently of the amplitude. In fact, this is only
approximately true, as was discovered by Christiaan Huygens.
Galileo also found that the square of the period varies directly with
the length of the pendulum. Galileo's son, Vincenzo, sketched a clock
based on his father's theories in 1642. The clock was never built and,
because of the large swings required by its verge escapement, would
have been a poor timekeeper. (See
Galileo is lesser known for, yet still credited with, being one of the
first to understand sound frequency. By scraping a chisel at different
speeds, he linked the pitch of the sound produced to the spacing of
the chisel's skips, a measure of frequency. In 1638, Galileo described
an experimental method to measure the speed of light by arranging that
two observers, each having lanterns equipped with shutters, observe
each other's lanterns at some distance. The first observer opens the
shutter of his lamp, and, the second, upon seeing the light,
immediately opens the shutter of his own lantern. The time between the
first observer's opening his shutter and seeing the light from the
second observer's lamp indicates the time it takes light to travel
back and forth between the two observers. Galileo reported that when
he tried this at a distance of less than a mile, he was unable to
determine whether or not the light appeared instantaneously.
Sometime between Galileo's death and 1667, the members of the
Accademia del Cimento
Accademia del Cimento repeated the experiment over a
distance of about a mile and obtained a similarly inconclusive
result. We now know that the speed of light is far too fast to be
measured by such methods (with human shutter-openers on Earth).
Galileo put forward the basic principle of relativity, that the laws
of physics are the same in any system that is moving at a constant
speed in a straight line, regardless of its particular speed or
direction. Hence, there is no absolute motion or absolute rest. This
principle provided the basic framework for
Newton's laws of motion
Newton's laws of motion and
is central to Einstein's special theory of relativity.
See also: Equations for a falling body
A biography by Galileo's pupil
Vincenzo Viviani stated that Galileo
had dropped balls of the same material, but different masses, from the
Leaning Tower of
Pisa to demonstrate that their time of descent was
independent of their mass. This was contrary to what Aristotle
had taught: that heavy objects fall faster than lighter ones, in
direct proportion to weight. While this story has been retold in
popular accounts, there is no account by Galileo himself of such an
experiment, and it is generally accepted by historians that it was at
most a thought experiment which did not actually take place.
An exception is Drake, who argues that the experiment did take
place, more or less as Viviani described it. The experiment described
was actually performed by
Simon Stevin (commonly known as Stevinus)
and Jan Cornets de Groot, although the building used was actually
the church tower in Delft in 1586. However, most of his
experiments with falling bodies were carried out using inclined planes
where both the issues of timing and air resistance were much reduced.
Apollo 15 mission in 1971, astronaut
David Scott showed
that Galileo was right: acceleration is the same for all bodies
subject to gravity on the Moon, even for a hammer and a feather.
In his 1638 Discorsi, Galileo's character Salviati, widely regarded as
Galileo's spokesman, held that all unequal weights would fall with the
same finite speed in a vacuum. But this had previously been proposed
by Lucretius and Simon Stevin. Cristiano Banti's Salviati
also held it could be experimentally demonstrated by the comparison of
pendulum motions in air with bobs of lead and of cork which had
different weight but which were otherwise similar.
Galileo proposed that a falling body would fall with a uniform
acceleration, as long as the resistance of the medium through which it
was falling remained negligible, or in the limiting case of its
falling through a vacuum. He also derived the correct kinematical
law for the distance travelled during a uniform acceleration starting
from rest—namely, that it is proportional to the square of the
elapsed time ( d ∝ t 2 ). Prior to
Galileo, Nicole Oresme, in the 14th century, had derived the
times-squared law for uniformly accelerated change, and Domingo
de Soto had suggested in the 16th century that bodies falling through
a homogeneous medium would be uniformly accelerated. Galileo
expressed the time-squared law using geometrical constructions and
mathematically precise words, adhering to the standards of the day.
(It remained for others to re-express the law in algebraic terms).
He also concluded that objects retain their velocity in the absence of
any impediments to their motion, thereby
contradicting the generally accepted Aristotelian hypothesis that a
body could only remain in so-called "violent", "unnatural", or
"forced" motion so long as an agent of change (the "mover") continued
to act on it. Philosophical ideas relating to inertia had been
John Philoponus and Jean Buridan. Galileo stated: "Imagine
any particle projected along a horizontal plane without friction; then
we know, from what has been more fully explained in the preceding
pages, that this particle will move along this same plane with a
motion which is uniform and perpetual, provided the plane has no
limits" This was incorporated into
Newton's laws of motion
Newton's laws of motion (first
While Galileo's application of mathematics to experimental physics was
innovative, his mathematical methods were the standard ones of the
day, including dozens of examples of an inverse proportion square root
method passed down from
Fibonacci and Archimedes. The analysis and
proofs relied heavily on the Eudoxian theory of proportion, as set
forth in the fifth book of Euclid's Elements. This theory had become
available only a century before, thanks to accurate translations by
Tartaglia and others; but by the end of Galileo's life, it was being
superseded by the algebraic methods of Descartes.
The concept now named
Galileo's paradox was not original with him. His
proposed solution, that infinite numbers cannot be compared, is no
longer considered useful.
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Nicolaus Copernicus publishes De revolutionibus orbium
coelestium as an alternative world system to the Ptolemy's geocentric
model causing subsequent questions to be raised about Aristotelian
physics following Copernicus' death
1563 – Parents
Vincenzo Galilei and Giulia Ammannati marry
1564 – Birth in Pisa, Italy
Thomas Digges publishes Pantometria describing a telescope
built between 1540–1559 by his father Leonard Digges
Tycho Brahe publishes De nova stella (On the new star)
refuting Aristotelian belief in immutable celestial spheres and an
eternal, unchanging, more perfect heavenly realm of celestial aether
above the moon
1576 – Giuseppe Moletti, Galileo's predecessor in the mathematics
chair at Padua, reports falling bodies of the same shape fall at the
same speed, regardless of material
1581 – His father,
Vincenzo Galilei publishes Dialogo della musica
antica et moderna formulating musical theories
1581 – Enrols as medical student at University of Pisa
1582 – Attends mathematics lecture by
Ostilio Ricci and decides to
study math and science
1585 – Leaves University of
Pisa without degree and works as tutor
1586 – Invents hydrostatic balance; wrote La Balancitta (The little
Simon Stevin publishes results for dropping lead weights from
Tycho Brahe publishes work on comets containing a description
Tychonic system of the world
1589 – Appointed to
Mathematics Chair, University of Pisa
~1590 – Partially completes De Motu (On Motion), which is never
1591 – Death of his father, Vicenzo Galilei
1592 – Appointed professor of mathematics at University of Padua,
remains 18 years
~1593 – Invents early thermometer that unfortunately depended on
both temperature and pressure
~1595 – Invents improved ballistics calculation geometric and
military compass, which he later improves for surveying and general
calculations and earns income from tutoring on its use
1597 – Letter to Kepler indicates his belief in the Copernican
1600 – First child, Virginia is born; ~1600 Le Meccaniche
1600 – William Gilbert publishes On the Magnet and Magnetic Bodies,
and on That Great Magnet the
Earth with arguments supporting the
Roman Inquisition finds Giordano Bruno, Copernican system
supporter, guilty of heresy for opinions on pantheism and the eternal
plurality of worlds, and for denial of the Trinity, divinity of
Christ, virginity of Mary, and Transubstantiation; burned at the stake
by civil authorities
1601 – Daughter Livia is born
1604 – Measures supernova position indicating no parallax for the
1605 – Sued by brothers-in-law for nonpayment of sisters' dowries
1606 – Son Vincenzo born
1606 – Publishes manual for his calculating compass
1607 – Rotilio Orlandini attempts to assassinate Galileo's friend,
Friar Paolo Sarpi
Hans Lippershey invents a refracting telescope
1609 – Independently invents and improves telescopes based on
description of invention by Hans Lippershey
1609 – Kepler publishes
Astronomia nova containing his first two
laws and for the first time demonstrates the Copernican model is more
accurate than the Ptolemaic for uses such as navigation and prediction
Thomas Harriot sketches the
Moon from telescopic observations
made four months before Galileo's
1610 – Publishes
Sidereus Nuncius (Starry Messenger); views our
moon's mountains and craters and brightest 4 of Jupiter's moons
1610 – Martin Horky publishes Brevissima Peregrinatio Contra Nuncium
Sidereum, opposing Galileo
1610 – Kepler requests one of
Galileo's telescopes or lenses, but
Galileo replies he is too busy to build one and has no extras
1610 – Lifetime appointment to mathematics position at University of
Padua, and as mathematician and philosopher for Cosimo II, Grand Duke
1611 – Discovers phases of Venus; granted audience with Pope; made
member of Lincean Academy
1611 – Awarded an honorary degree by the
Jesuit College in Rome
David Fabricius publishes Narration on Spots Observed on the
Sun and their Apparent Rotation with the
Sun prior to Christoph
Scheiner and Galileo's published works on the subject
1612 – Proposed Jupiter's moons could be used as a universal clock
for possible determination of longitude
~1612 or 1613 –
Francesco Sizzi discovers annual variations in
1613 – Letters on Sunspots
1613 – Letter to
Benedetto Castelli discussing the rotation of the
sun and Galileo's support of the Copernican system. Using Biblical
inerrancy as a basis, Galileo writes that Joshua's command for the sun
to stand still in
Joshua 10:13 proves the "impossibility of the
Aristotelian and Ptolemaic world system, and on the other hand agrees
very well with the Copernican one." He went on to write that "the
sun gives not only light (as it obviously does) but also motion to all
the planets that revolve around it" by its rotation.
Letter to Grand Duchess Christina
Letter to Grand Duchess Christina (not published until 1636)
1616 – Officially warned by the Church not to hold or defend the
1616 – The
Catholic Church places De revolutionibus orbium
coelestium on the List of Prohibited Books, pending correction
1616 – Private letter "Discourse on the Tides"
1617 – Moves into Bellosguardo, west of Florence, near his
daughters' convent; observes double star Mizar in Ursa Major
1619 – Kepler publishes
Harmonices Mundi which introduces his third
1619 – Discourse on the Comets
1623 – Maffeo
Barberini becomes Pope Urban VIII
1623 – Publishes The Assayer
1624 – Visits Pope who praises and honours him, leaving with assumed
permission to publish work on the Copernican vs. Ptolemaic Systems;
used a compound microscope
1625 – Illustrations of insects made using one of Galileo's
1630 – Completes
Dialogue Concerning the Two Chief World Systems
Dialogue Concerning the Two Chief World Systems and
subsequently receives approval of Church censor
1630 - Invited by Grand Duke Ferdinand II of Tuscany to advise on
proposed engineering works on the Bisenzio River
1631 - Produces report on the Bisenzio engineering proposals, arguing
1632 – Publishes Dialogue Concerning the Two Chief World Systems
1633 – sentenced by the
Inquisition to imprisonment, commuted to
house arrest, for vehement suspicion of heresy in violating the 1616
Catholic Church places Dialogue Concerning the Two Chief
World Systems on the List of Prohibited Books
1638 – Publishes Dialogues Concerning Two New Sciences
1642 – Death in Arcetri, Italy
Isaac Newton builds his reflecting telescope
1687 – Newton publishes Philosophiæ Naturalis Principia Mathematica
deriving Kepler's laws from the Universal Law of Gravitation and the
Laws of Motion
2016 – The American Juno spacecraft, carrying a plaque and a Lego
minifigure dedicated at Galileo, arrives at Jupiter's orbit
Later Church reassessments
Galileo affair was largely forgotten after Galileo's death, and
the controversy subsided. The Inquisition's ban on reprinting
Galileo's works was lifted in 1718 when permission was granted to
publish an edition of his works (excluding the condemned Dialogue) in
Florence. In 1741,
Pope Benedict XIV
Pope Benedict XIV authorised the publication
of an edition of Galileo's complete scientific works which
included a mildly censored version of the Dialogue. In 1758, the
general prohibition against works advocating heliocentrism was removed
from the Index of prohibited books, although the specific ban on
uncensored versions of the Dialogue and Copernicus's De Revolutionibus
remained. All traces of official opposition to heliocentrism by
the church disappeared in 1835 when these works were finally dropped
from the Index.
Interest in the
Galileo affair was revived in the early 19th century,
when Protestant polemicists used it (and other events such as the
Inquisition and the myth of the flat Earth) to attack Roman
Catholicism. Interest in it has waxed and waned ever since. In
1939, Pope Pius XII, in his first speech to the Pontifical Academy of
Sciences, within a few months of his election to the papacy, described
Galileo as being among the "most audacious heroes of research... not
afraid of the stumbling blocks and the risks on the way, nor fearful
of the funereal monuments". His close advisor of 40 years,
Professor Robert Leiber, wrote: "Pius XII was very careful not to
close any doors (to science) prematurely. He was energetic on this
point and regretted that in the case of Galileo."
On 15 February 1990, in a speech delivered at the Sapienza University
of Rome, Cardinal Ratzinger (later Pope Benedict XVI) cited some
current views on the
Galileo affair as forming what he called "a
symptomatic case that permits us to see how deep the self-doubt of the
modern age, of science and technology goes today". Some of the
views he cited were those of the philosopher Paul Feyerabend, whom he
quoted as saying "The Church at the time of Galileo kept much more
closely to reason than did Galileo himself, and she took into
consideration the ethical and social consequences of Galileo's
teaching too. Her verdict against Galileo was rational and just and
the revision of this verdict can be justified only on the grounds of
what is politically opportune." The Cardinal did not clearly
indicate whether he agreed or disagreed with Feyerabend's assertions.
He did, however, say "It would be foolish to construct an impulsive
apologetic on the basis of such views."
On 31 October 1992,
Pope John Paul II
Pope John Paul II expressed regret for how the
Galileo affair was handled, and issued a declaration acknowledging the
errors committed by the
Catholic Church tribunal that judged the
scientific positions of Galileo Galilei, as the result of a study
conducted by the Pontifical Council for Culture. In March
2008, the head of the Pontifical Academy of Sciences, Nicola Cabibbo,
announced a plan to honour Galileo by erecting a statue of him inside
the Vatican walls. In December of the same year, during events to
mark the 400th anniversary of Galileo's earliest telescopic
Pope Benedict XVI
Pope Benedict XVI praised his contributions to
astronomy. A month later, however, the head of the Pontifical
Council for Culture, Gianfranco Ravasi, revealed that the plan to
erect a statue of Galileo in the grounds of the Vatican had been
Impact on modern science
According to Stephen Hawking, Galileo probably bears more of the
responsibility for the birth of modern science than anybody else,
Albert Einstein called him the father of modern science.
International Year of
Astronomy commemorative coin
Galileo's astronomical discoveries and investigations into the
Copernican theory have led to a lasting legacy which includes the
categorisation of the four large moons of
Jupiter discovered by
Galileo (Io, Europa, Ganymede and Callisto) as the Galilean moons.
Other scientific endeavours and principles are named after Galileo
including the Galileo spacecraft, the first spacecraft to enter
orbit around Jupiter, the proposed Galileo global satellite navigation
system, the transformation between inertial systems in classical
Galilean transformation and the Gal (unit),
sometimes known as the Galileo, which is a non-SI unit of
Partly because 2009 was the fourth centenary of Galileo's first
recorded astronomical observations with the telescope, the United
Nations scheduled it to be the International Year of Astronomy. A
global scheme was laid out by the International Astronomical Union
(IAU), also endorsed by UNESCO—the UN body responsible for
educational, scientific and cultural matters. The International Year
Astronomy 2009 was intended to be a global celebration of astronomy
and its contributions to society and culture, stimulating worldwide
interest not only in astronomy but science in general, with a
particular slant towards young people.
697 Galilea is named in his honour.
In artistic and popular media
Galileo is mentioned several times in the "opera" section of the Queen
song, "Bohemian Rhapsody". He features prominently in the song
"Galileo" performed by the
Indigo Girls and Amy Grant's Galileo on her
Heart in Motion album.
Twentieth-century plays have been written on Galileo's life, including
Life of Galileo
Life of Galileo (1943) by the German playwright Bertolt Brecht, with a
film adaptation (1975) of it, and
Lamp At Midnight
Lamp At Midnight (1947) by Barrie
Stavis, as well as the 2008 play "Galileo Galilei".
Kim Stanley Robinson
Kim Stanley Robinson wrote a science fiction novel entitled Galileo's
Dream (2009), in which Galileo is brought into the future to help
resolve a crisis of scientific philosophy; the story moves back and
forth between Galileo's own time and a hypothetical distant future and
contains a great deal of biographical information.
Galileo Galilei was recently selected as a main motif for a high value
collectors' coin: the €25 International Year of Astronomy
commemorative coin, minted in 2009. This coin also commemorates the
400th anniversary of the invention of Galileo's telescope. The obverse
shows a portion of his portrait and his telescope. The background
shows one of his first drawings of the surface of the moon. In the
silver ring, other telescopes are depicted: the Isaac Newton
Telescope, the observatory in Kremsmünster Abbey, a modern telescope,
a radio telescope and a space telescope. In 2009, the
also released. This is a mass-produced, low-cost educational 2-inch
(51 mm) telescope with relatively high quality.
Statue outside the Uffizi, Florence
Galileo's early works describing scientific instruments include the
1586 tract entitled The Little Balance (La Billancetta) describing an
accurate balance to weigh objects in air or water and the 1606
printed manual Le Operazioni del Compasso Geometrico et Militare on
the operation of a geometrical and military compass.
His early works in dynamics, the science of motion and mechanics were
his circa 1590 Pisan De Motu (On Motion) and his circa 1600 Paduan Le
Meccaniche (Mechanics). The former was based on
Aristotelian–Archimedean fluid dynamics and held that the speed of
gravitational fall in a fluid medium was proportional to the excess of
a body's specific weight over that of the medium, whereby in a vacuum,
bodies would fall with speeds in proportion to their specific weights.
It also subscribed to the Philoponan impetus dynamics in which impetus
is self-dissipating and free-fall in a vacuum would have an essential
terminal speed according to specific weight after an initial period of
Galileo's 1610 The Starry Messenger (Sidereus Nuncius) was the first
scientific treatise to be published based on observations made through
a telescope. It reported his discoveries of:
the Galilean moons
the roughness of the Moon's surface
the existence of a large number of stars invisible to the naked eye,
particularly those responsible for the appearance of the Milky Way
differences between the appearances of the planets and those of the
fixed stars—the former appearing as small discs, while the latter
appeared as unmagnified points of light
Galileo published a description of sunspots in 1613 entitled Letters
on Sunspots suggesting the
Sun and heavens are corruptible. The
Sunspots also reported his 1610 telescopic observations of
the full set of phases of Venus, and his discovery of the puzzling
Saturn and their even more puzzling subsequent
disappearance. In 1615, Galileo prepared a manuscript known as the
"Letter to the Grand Duchess Christina" which was not published in
printed form until 1636. This letter was a revised version of the
Letter to Castelli, which was denounced by the
Inquisition as an
incursion upon theology by advocating Copernicanism both as physically
true and as consistent with Scripture. In 1616, after the order
by the inquisition for Galileo not to hold or defend the Copernican
position, Galileo wrote the "Discourse on the Tides" (Discorso sul
flusso e il reflusso del mare) based on the Copernican earth, in the
form of a private letter to Cardinal Orsini. In 1619, Mario
Guiducci, a pupil of Galileo's, published a lecture written largely by
Galileo under the title Discourse on the Comets (Discorso Delle
Comete), arguing against the
Jesuit interpretation of comets.
In 1623, Galileo published The Assayer—Il Saggiatore, which attacked
theories based on Aristotle's authority and promoted experimentation
and the mathematical formulation of scientific ideas. The book was
highly successful and even found support among the higher echelons of
the Christian church. Following the success of The Assayer,
Galileo published the Dialogue Concerning the Two Chief World Systems
(Dialogo sopra i due massimi sistemi del mondo) in 1632. Despite
taking care to adhere to the Inquisition's 1616 instructions, the
claims in the book favouring Copernican theory and a non Geocentric
model of the solar system led to Galileo being tried and banned on
publication. Despite the publication ban, Galileo published his
Discourses and Mathematical Demonstrations Relating to Two New
Sciences (Discorsi e Dimostrazioni Matematiche, intorno a due nuove
scienze) in 1638 in Holland, outside the jurisdiction of the
Published written works
Galileo's main written works are as follows:
The Little Balance (1586; in Italian: La Billancetta)
On Motion (c. 1590; in Latin: De Motu Antiquiora)
Mechanics (c. 1600; in Italian: Le mecaniche)
The Operations of Geometrical and Military Compass (1606; in Italian:
Le operazioni del compasso geometrico et militare)
The Starry Messenger (1610; in Latin: Sidereus Nuncius)
Discourse on Floating Bodies (1612; in Italian: Discorso intorno alle
cose che stanno in su l'acqua, o che in quella si muovono, "Discourse
on Bodies that Stay Atop Water, or Move in It")
History and Demonstration Concerning
Sunspots (1613; in Italian:
Istoria e dimostrazioni intorno alle macchie solari; work based on the
Three Letters on Sunspots, Tre lettere sulle macchie solari, 1612)
"Letter to the Grand Duchess Christina" (1615; published in 1636)
"Discourse on the Tides" (1616; in Italian: Discorso del flusso e
reflusso del mare)
Discourse on the Comets (1619; in Italian: Discorso delle Comete)
The Assayer (1623; in Italian: Il Saggiatore)
Dialogue Concerning the Two Chief World Systems
Dialogue Concerning the Two Chief World Systems (1632; in Italian:
Dialogo sopra i due massimi sistemi del mondo)
Discourses and Mathematical Demonstrations Relating to Two New
Sciences (1638; in Italian: Discorsi e Dimostrazioni Matematiche,
intorno a due nuove scienze)
History of science
History of science portal
Aristarchus of Samos
Catholic Church and science
Dialogo de Cecco di Ronchitti da Bruzene in perpuosito de la stella
Seleucus of Seleucia
Tribune of Galileo
Tribune of Galileo (memorial in the
Villa Il Gioiello
Villa Il Gioiello (Galileo's main home in Florence)
^ F. Vinci,
Ostilio Ricci da Fermo, Maestro di Galileo Galilei, Fermo,
Mathematics Genealogy Project - Galileo Galilei".
^ Drake (1978, p. 1). The date of Galileo's birth is given according
to the Julian calendar, which was then in force throughout
Christendom. In 1582 it was replaced in Italy and several other
Catholic countries with the Gregorian calendar. Unless otherwise
indicated, dates in this article are given according to the Gregorian
^ a b c d e f Hannam, James (2011). The Genesis of Science. pp.
^ Sharratt (1994, pp. 127–131), McMullin (2005a).
^ Finocchiaro, Maurice (2010). Defending Copernicus and Galileo:
Critical Reasoning in the Two Affairs. Springer. p. 74.
ISBN 9789048132010. Retrieved 21 May 2016.
^ Finocchiaro (1997), p. 47.
^ Hilliam (2005), p. 96.
^ a b c Carney, Jo Eldridge (2000). Renaissance and Reformation,
1500–1620: a. Greenwood Publishing. ISBN 0-313-30574-9.
^ a b Allan-Olney (1870)
^ Singer, Charles (1941). "A Short History of
Science to the
Nineteenth Century". Clarendon Press: 217.
^ Whitehouse, David (2009). Renaissance Genius:
Galileo Galilei &
His Legacy to Modern Science. Sterling Publishing. p. 219.
^ Weidhorn, Manfred (2005). The Person of the Millennium: The Unique
Impact of Galileo on World History. iUniverse. p. 155.
^ Thomas Hobbes: Critical Assessments, Volume 1. Preston King. 1993.
^ Finocchiaro (2007).
^ Disraeli, Isaac (1835). Curiosities of Literature. W. Pearson &
Company. p. 371.
^ O'Connor, J. J.; Robertson, E.F. "Galileo Galilei". The MacTutor
Mathematics archive. University of St Andrews, Scotland.
^ John Gribbin. The Fellowship: Gilbert, Bacon, Harvey, Wren, Newton
and the Story of the Scientific Revolution. The Overlook Press, 2008.
^ Gribbin, John (2009) . Science. A History. 1543–2001.
London: Penguin UK. p. 107. ISBN 978-0-141-04222-0.
^ Sobel (1999, p. 16)
^ Sobel (1999, p. 13)
^ "Galilean". The Century Dictionary and Encyclopedia. III. New York:
The Century Co. 1903 . p. 2436.
^ Sobel (1999, p. 16) "The meaning of the name Galileo, or Galilei,
harks back to the land of Galilee, although, as Galileo explained on
this score, he was not at all a Jew."
^ Maurice Finnochiaro, The Galileo Affair: A Documentary History 300,
330 n. 13 (Univ. Cal. Press 1998)
^ Naess, Atle (2004).
Galileo Galilei - When the World Stood Still.
Science & Business Media. pp. 89–91.
ISBN 9783540270546. Retrieved 2 November 2016.
^ Sharratt (1994, pp. 17, 213)
^ Rosen, Joe; Gothard, Lisa Quinn (2009). Encyclopedia of Physical
Science. Infobase Publishing. p. 268. ISBN 978-0-8160-7011-4.
^ Gribbin. John (2008). The Fellowship: Gilbert, Bacon, Harvey, Wren,
Newton and the Story of the Scientific Revolution. Overlook Press. p.
^ Sobel (2000, p. 5) Chapter 1. Retrieved on 14 January 2017. "But
because he never married Virginia's mother, he deemed the girl herself
unmarriageable. Soon after her thirteenth birthday, he placed her at
the Convent of San Matteo in Arcetri."
^ Pedersen, Olaf (1985). "Galileo's Religion". In Coyne, George V.;
Heller, Michał; Życiński, Józef. The Galileo Affair: A Meeting of
Faith and Science, Proceedings of the Cracow Conference, May 24–27,
1984. Vatican City: Specola Vaticana. pp. 75–102.
Bibcode:1985gamf.conf...75P. OCLC 16831024.
^ Reston (2000, pp. 3–14).
^ a b c Asimov, Isaac (1964). Asimov's Biographical Encyclopedia of
Science and Technology. ISBN 978-0385177719
^ a b Edgerton, Samuel Y. The Mirror, the Window, and the Telescope,
^ a b Panofsky, Erwin (1956). "Galileo as a Critic of the Arts:
Aesthetic Attitude and Scientific Thought". Isis. 47 (1): 3–15.
doi:10.1086/348450. JSTOR 227542.
^ Sharratt (1994, pp. 45–66).
^ Rutkin, H. Darrel. "Galileo, Astrology, and the Scientific
Revolution: Another Look". Program in History & Philosophy of
Science & Technology, Stanford University. Retrieved
^ Finocchiaro (1989), pp. 67–9.
^ Finocchiaro (1989), p. 354, n. 52
^ Finocchiaro (1989), pp. 119–133
^ Finocchiaro (1989), pp. 127–131 and Galilei, (1953), pp. 432–6
^ Einstein (1953) p. xvii
^ Galilei, (1953), p. 462.
^ James Robert Voelkel. The Composition of Kepler's Astronomia Nova.
Princeton University Press, 2001. p. 74
^ Stillman Drake. Essays on Galileo and the History and Philosophy of
Science, Volume 1. University of Toronto Press, 1999. p. 343
^ Drake (1960, pp.vii, xxiii–xxiv), Sharratt (1994, pp. 139–140).
^ Grassi (1960a).
^ Drake (1978, p. 268), Grassi (1960a, p. 16).
^ Galilei & Guiducci (1960).
^ Drake (1960, p.xvi).
^ Drake (1957, p. 222), Drake (1960, p.xvii).
^ Sharratt (1994, p. 135), Drake (1960, p.xii), Galilei & Guiducci
(1960, p. 24).
^ Sharratt (1994, p. 135).
^ Sharratt (1994, p. 135), Drake (1960, p.xvii).
^ Grassi (1960b).
^ Drake (1978, p. 494), Favaro(1896, 6:111) Archived 8 January 2009 at
the Wayback Machine.. The pseudonym was a slightly imperfect anagram
of Oratio Grasio Savonensis, a Latinised version of his name and home
^ Galilei (1960).
^ Sharratt (1994, p. 137), Drake (1957, p. 227).
^ Sharratt (1994, p. 138–142).
^ Drake (1960, p.xix).
^ Alexander, Amir (2014). Infinitesimal: How a Dangerous Mathematical
Theory Shaped the Modern World.
Scientific American / Farrar, Straus
and Giroux. p. 131. ISBN 978-0374176815.
^ Drake (1960, p.vii).
^ Sharratt (1994, p. 175).
^ Sharratt (1994, pp. 175–78), Blackwell (2006, p. 30).
^ Blackwell, Richard (1991). Galileo, Bellarmine, and the Bible. Notre
Dame: University of Notre Dame Press. p. 25.
^ a b Hannam, James. "The Genesis of Science". 2011. p303-316.
^ "The Gregorian calendar, first adopted in 1582, was based on
computations that made use of Copernicus' work" (Kuhn, Thomas (1957),
The Copernican Revolution, Harvard University Press,
p. 125 ).
^ Graney and Danielson (2014).
^ Brodrick (1965, c1964, p. 95) quoting Cardinal Bellarmine's letter
to Foscarini, dated 12 April 1615. Translated from Favaro (1902,
12:171–72) (in Italian).
^ Finocchiaro (1989), pp. 27-28.
^ Langford (1992), pp. 56–57
^ Finocchiaro (1989), pp. 28 & 134.
^ Graney (2015, pp. 68-69) Ingoli's essay was published in English
translation for the first time in 2015.
^ Finocchiaro (2010, pp. 72)
^ Graney (2015, pp. 71)
^ Graney (2015, pp. 66-76, 164-175, 187-195)
^ Finocchiaro, Maurice. "West Chester University—History of
Astronomy; Lecture notes: Texts from The Galileo Affair: A Documentary
History". West Chester University. ESS 362 / 562. Archived from the
original on 30 September 2007. Retrieved 18 February 2014.
^ "Una errata reproducida durante siglos cambia la censura de la
Iglesia a Galileo". Materia.
^ a b Heilbron (2010), p. 218
^ Sharratt (1994, pp. 126–31).
Pope Urban VIII
Pope Urban VIII Biography". Galileo Project.
^ Finocchiaro (1997), p. 82; Moss & Wallace (2003), p. 11
^ See Langford (1966, pp. 133–34), and Seeger (1966, p. 30), for
example. Drake (1978, p. 355) asserts that Simplicio's character is
modelled on the Aristotelian philosophers Lodovico delle Colombe and
Cesare Cremonini, rather than Urban. He also considers that the demand
for Galileo to include the Pope's argument in the Dialogue left him
with no option but to put it in the mouth of Simplicio (Drake, 1953,
p. 491). Even Arthur Koestler, who is generally quite harsh on Galileo
in The Sleepwalkers (1959), after noting that Urban suspected Galileo
of having intended Simplicio to be a caricature of him, says "this of
course is untrue" (1959, p. 483).
^ Lindberg, David. "Beyond War and Peace: A Reappraisal of the
Encounter between Christianity and Science".
^ Sharratt (1994, pp. 171–75); Heilbron (2010, pp. 308–17);
Gingerich (1992, pp. 117–18).
^ Fantoli (2005, p. 139), Finocchiaro (1989, pp. 288–93).
Finocchiaro's translation of the Inquisition's judgement against
Galileo is "available on-line". Archived from the original on 30
September 2007. Retrieved 2007-09-30. . "Vehemently suspect of
heresy" was a technical term of canon law and did not necessarily
imply that the
Inquisition considered the opinions giving rise to the
verdict to be heretical. The same verdict would have been possible
even if the opinions had been subject to only the less serious censure
of "erroneous in faith" (Fantoli, 2005, p. 140; Heilbron, 2005, pp.
^ Finocchiaro (1989, pp. 38, 291, 306). Finocchiaro's translation of
the Inquisition's judgement against Galileo is "available on-line".
Archived from the original on 30 September 2007. Retrieved
^ Drake (1978, p. 367), Sharratt (1994, p. 184), Favaro(1905, 16:209
Archived 27 September 2007 at the Wayback Machine., 230) Archived 27
September 2007 at the Wayback Machine. (in Italian). See Galileo
affair for further details.
^ Drake (1978, p. 356-7).
^ Shea, William (January 2006). "The Galileo Affair" (unpublished
work). Grupo de Investigación sobre Ciencia, Razón y Fe (CRYF).
Retrieved 12 September 2010.
^ Stephen Hawking, ed. p. 398, On the Shoulders of Giants: "Galileo...
is the father of modern physics—indeed of modern science"—Albert
^ Sobel (2000, pp. 232–4).
^ Gerard, John (1909). "Galileo Galilei". In Herbermann, Charles.
Catholic Encyclopedia. New York: Robert Appleton.
^ Shea & Artigas (2003, p. 199); Sobel (2000, p. 378).
^ Shea & Artigas (2003, p. 199); Sobel (2000, p. 378); Sharratt
(1994, p. 207); Favaro(1906,18:378–80) Archived 3 January 2008 at
the Wayback Machine. (in Italian).
^ Monumental tomb of Galileo. Institute and Museum of the History of
Science, Florence, Italy. Retrieved 2010-02-15.
^ Shea & Artigas (2003, p. 199); Sobel (2000, p. 380).
^ Shea & Artigas (2003, p. 200); Sobel (2000, pp. 380–384).
^ Section of Room VII Galilean iconography and relics, Museo Galileo.
Accessed on line 27 May 2011.
^ Middle finger of Galileo's right hand, Museo Galileo. Accessed on
line 27 May 2011.
^ Sharratt (1994, pp. 204–05)
^ Cohen, H. F. (1984). Quantifying Music: The
Science of Music at.
Springer. pp. 78–84. ISBN 90-277-1637-4.
^ Field, Judith Veronica (2005). Piero Della Francesca: A
Mathematician's Art. Yale University Press. pp. 317–320.
^ In Drake (1957, pp. 237–238)
^ Wallace, (1984).
^ Sharratt (1994, pp. 202–04), Galilei (1954, pp. 250–52), Favaro
(1898), 8:274–75 Archived 27 September 2007 at the Wayback Machine.
^ Sharratt (1994, pp. 202–04), Galilei (1954, pp. 252), Favaro
(1898), 8:275 Archived 8 January 2009 at the Wayback Machine. (in
^ King (2003, pp.30–32). The Netherlands States-General would not
grant Lippershey his requested patent (King, 2003, p.32).
^ Drake (1990, pp. 133–34).
^ Sharratt (1994, pp. 1–2)
^ Kollerstrom, Nicholas (October 2004). "Galileo and the new star"
Astronomy Now. 18 (10): 58–59. Bibcode:2004AsNow..18j..58K.
ISSN 0951-9726. Retrieved 20 February 2017.
^ i.e., invisible to the naked eye.
^ Drake (1978, p. 146).
Sidereus Nuncius (Favaro, 1892, 3:81 Archived 27 January 2012 at
the Wayback Machine. (in Latin)) Galileo stated that he had reached
this conclusion on 11 January. Drake (1978, p. 152), however, after
studying unpublished manuscript records of Galileo's observations,
concluded that he did not do so until 15 January.
^ Sharratt (1994, p. 17).
^ Linton (2004, pp. 98,205), Drake (1978, p. 157).
^ Drake (1978, pp. 158–68), Sharratt (1994, pp. 18–19).
^ God's Philosophers ju James Hannam Orion 2009 p313
^ Drake (1978, p. 168), Sharratt (1994, p. 93).
^ Thoren (1989), p. 8; Hoskin (1999) p. 117.
^ In the Capellan model only Mercury and
Venus orbit the Sun, whilst
in its extended version such as expounded by Riccioli, Mars also
orbits the Sun, but the orbits of
Saturn are centred on
^ Baalke, Ron. Historical Background of Saturn's Rings. Archived 21
March 2009 at the Wayback Machine. Jet Propulsion Laboratory,
California Institute of Technology, NASA. Retrieved on 2007-03-11
^ Drake & Kowal (1980)
^ Vaquero, J.M.; Vázquez, M. (2010). The
Sun Recorded Through
History. Springer. Chapter 2, p. 77: "Drawing of the large
sunspot seen by naked-eye by Galileo, and shown in the same way to
everybody during the days 19, 20, and 21 August 1612"
^ Drake (1978, p. 209). Sizzi reported the observations he and his
companions had made over the course of a year to Orazio Morandi in a
letter dated 10 April 1613 (Favaro, 1901, 11:491) Archived 8 January
2009 at the Wayback Machine. (in Italian). Morandi subsequently
forwarded a copy to Galileo.
^ In geostatic systems the apparent annual variation in the motion of
sunspots could only be explained as the result of an implausibly
complicated precession of the Sun's axis of rotation (Linton, 2004, p.
212; Sharratt, 1994, p. 166; Drake, 1970, pp. 191–196). This did not
apply, however, to the modified version of Tycho's system introduced
by his protegé, Longomontanus, in which the
Earth was assumed to
rotate. Longomontanus's system could account for the apparent motions
of sunspots just as well as the Copernican.
^ Ondra (2004), p. 72–73
^ Graney (2010, p. 455); Graney & Grayson (2011, p. 353).
^ Van Helden, (1985, p. 75); Chalmers, (1999, p. 25); Galilei (1953,
^ Finocchiaro (1989, pp. 167–76), Galilei (1953, pp. 359–60),
Ondra (2004, pp. 74–5).
^ Graney (2010, p. 454-462); Graney & Grayson (2011, p. 352-355).
^ Reston (2000, p. 56).
^ Sobel (2000, p. 43), Drake (1978, p. 196). In the Starry Messenger,
written in Latin, Galileo had used the term "perspicillum".
^ Rosen, Edward, The Naming of the
^ Drake (1978, pp. 163–164), Favaro(1892, 3:163 Archived 27
September 2007 at the Wayback Machine.–164) Archived 22 October 2007
at the Wayback Machine.(in Latin)
^ Probably in 1623, according to Drake (1978, p. 286).
^ Drake (1978, p. 289), Favaro(1903, 13:177) Archived 27 September
2007 at the Wayback Machine. (in Italian).
^ Drake (1978, p. 286), Favaro(1903, 13:208) Archived 27 September
2007 at the Wayback Machine. (in Italian). The actual inventors of the
telescope and microscope remain debatable. A general view on this can
be found in the article
Hans Lippershey (last updated 2003-08-01), ©
1995–2007 by Davidson, Michael W. and the Florida State University.
^ "brunelleschi.imss.fi.it "Il microscopio di Galileo"" (PDF).
Archived from the original (PDF) on 9 April 2008.
^ Van Helden, Al. Galileo Timeline (last updated 1995), The Galileo
Project. Retrieved 2007-08-28. See also Timeline of microscope
^ Drake (1978, p. 286).
^ Longitude: the true story of a lone genius who solved the greatest
scientific problem of his time,
Dava Sobel Penguin, 1996
ISBN 0-14-025879-5, ISBN 978-0-14-025879-0
^ Cesare S. Maffioli (2008). "Galileo, Guiducci and the Engineer
Bartolotti on the Bisenzio River". academia.edu. Galileana (V).
Retrieved 11 August 2017.
^ Newton, R. G. (2004). Galileo's Pendulum: From the Rhythm of Time to
the Making of Matter. Harvard University Press. p. 51.
^ Galileo Galilei, Two New Sciences, (Madison: Univ. of Wisconsin Pr.,
1974) p. 50.
^ I. Bernard Cohen, "Roemer and the First Determination of the
Velocity of Light (1676)", Isis, 31 (1940): 327–379, see pp.
^ Drake (1978, pp. 19,20). At the time when Viviani asserts that the
experiment took place, Galileo had not yet formulated the final
version of his law of free fall. He had, however, formulated an
earlier version which predicted that bodies of the same material
falling through the same medium would fall at the same speed (Drake,
1978, p. 20).
^ Drake (1978, p. 9); Sharratt (1994, p. 31).
^ Groleau, Rick. "Galileo's Battle for the Heavens. July 2002".
Ball, Phil (2005-06-30). "
Science history: setting the record
straight. 30 June 2005". The Hindu. Chennai, India.
^ Heilbron, John L. (2015), "That Galileo publicly refuted Aristotle's
conclusions about motion by repeated experiments made from the
campanile of Pisa", in Numbers, Ronald L.; Kampourakis, Kostas,
Newton's Apple and Other Myths about Science, Harvard University
Press, pp. 40–47, ISBN 9780674915473
^ Drake (1978, pp. 19–21, 414–416)
^ Galileo Galilei: The Falling Bodies Experiment. Last accessed 26 Dec
^ Lucretius, De rerum natura II, 225–229; Relevant passage appears
in: Lane Cooper, Aristotle, Galileo, and the Tower of
N.Y.: Cornell University Press, 1935), p. 49.
^ Simon Stevin, De Beghinselen des Waterwichts, Anvang der
Waterwichtdaet, en de Anhang komen na de Beghinselen der Weeghconst en
de Weeghdaet [The Elements of Hydrostatics, Preamble to the Practice
of Hydrostatics, and Appendix to The Elements of the Statics and The
Practice of Weighing] (Leiden, Netherlands: Christoffel Plantijn,
1586) reports an experiment by Stevin and Jan Cornets de Groot in
which they dropped lead balls from a church tower in Delft; relevant
passage is translated in: E. J. Dijksterhuis, ed., The Principal Works
Simon Stevin Amsterdam, Netherlands: C. V. Swets & Zeitlinger,
1955 vol. 1, pp. 509, 511.
^ Sharratt (1994, p. 203), Galilei (1954, pp. 251–54).
^ Sharratt (1994, p. 198), Galilei (1954, p. 174).
^ Clagett (1968, p. 561). Oresme, however, regarded this discovery as
a purely intellectual exercise having no relevance to the description
of any natural phenomena, and consequently failed to recognise any
connection with the motion of falling bodies (Grant, 1996, p.103).
^ Sharratt (1994, p. 198), Wallace (2004, pp.II 384, II 400, III 272)
Soto, however, did not anticipate many of the qualifications and
refinements contained in Galileo's theory of falling bodies. He did
not, for instance, recognise, as Galileo did, that a body would fall
with a strictly uniform acceleration only in a vacuum, and that it
would otherwise eventually reach a uniform terminal velocity.
^ Jung (2011, p.504). This aspect of Aristotle's theory of motion is
covered in Books VII and VIII of his Physics.
^ Galilei, (1954, p.268) or Inertia#Classical inertia
^ Giuseppe Moleti, Walter Roy Laird. The unfinished mechanics of
Giuseppe Moletti. University of Toronto Press, 1999. p. 5
^ Robert Henry Herman, Vincenzo Galilei. Dialogo della musica antica
et della moderna of Vincenzo Galilei: translation and commentary, Part
1. North Texas State University, 1973. p. 17
^ Adam, Mosley. "Tycho Brahe". Starry Messenger. History &
Science Dept, University of Cambridge. Retrieved 13
^ Timothy Ferris. Coming of Age in the Milky Way. William Morrow &
Company, Inc. 1988. p. 95
^ Shea, William; Artigas, Mariano. "The Galileo Affair".
^ a b Galileo Galilei, "Letter to
Benedetto Castelli (1613)", Religion
and Science. (Source of the English translation. Archived 6 February
2011 at the Wayback Machine.)
^ Heilbron (2005, p. 299).
^ Two of his non-scientific works, the letters to Castelli and the
Grand Duchess Christina, were explicitly not allowed to be included
(Coyne 2005, p. 347).
^ Heilbron (2005, pp. 303–04); Coyne (2005, p. 347). The uncensored
version of the Dialogue remained on the Index of prohibited books,
however (Heilbron 2005, p. 279).
^ Heilbron (2005, p. 307); Coyne (2005, p. 347) The practical effect
of the ban in its later years seems to have been that clergy could
publish discussions of heliocentric physics with a formal disclaimer
assuring its hypothetical character and their obedience to the church
decrees against motion of the earth: see for example the commented
edition (1742) of Newton's 'Principia' by Fathers Le Seur and
Jacquier, which contains such a disclaimer ('Declaratio') before the
third book (Propositions 25 onwards) dealing with the lunar theory.
^ McMullin (2005, p. 6); Coyne (2005, p. 346). In fact, the Church's
opposition had effectively ended in 1820 when a Catholic canon,
Giuseppe Settele, was given permission to publish a work which treated
heliocentrism as a physical fact rather than a mathematical fiction.
The 1835 edition of the Index was the first to be issued after that
^ Discourse of His Holiness
Pope Pius XII
Pope Pius XII given on 3 December 1939 at
the Solemn Audience granted to the Plenary Session of the Academy,
Discourses of the Popes from Pius XI to John Paul II to the Pontifical
Academy of the Sciences 1939–1986, Vatican City, p. 34
^ Robert Leiber, Pius XII Stimmen der Zeit, November 1958 in Pius XII.
Sagt, Frankfurt 1959, p. 411
^ An earlier version had been delivered on 16 December 1989, in Rieti,
and a later version in Madrid on 24 February 1990 (Ratzinger, 1994, p.
81). According to Feyerabend himself, Ratzinger had also mentioned him
"in support of" his own views in a speech in Parma around the same
time (Feyerabend, 1995, p. 178).
^ a b c Ratzinger (1994, p. 98).
^ "Vatican admits Galileo was right".
New Scientist (1846).
1992-11-07. Retrieved 2007-08-09. .
^ "Papal visit scuppered by scholars". BBC News. 2008-01-15. Retrieved
^ Owen & Delaney (2008).
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