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Galileo Galilei (Italian pronunciation: [ɡaliˈlɛːo
ɡaliˈlɛi]; 15 February 1564[4] – 8 January 1642),[5] was an Italian physicist,
mathematician, astronomer, and philosopher who played a major role in the
Scientific Revolution. His achievements include improvements to the telescope
and consequent astronomical observations and support for Copernicanism. Galileo
has been called the "father of modern observational astronomy",[6]
the "father of modern physics",[7] the "father of
science",[7] and "the Father of Modern Science".[8]
His contributions to observational astronomy include the
telescopic confirmation of the phases of Venus, the discovery of the four
largest satellites of Jupiter (named the Galilean moons in his honour), and the
observation and analysis of sunspots. Galileo also worked in applied science
and technology, inventing an improved military compass and other instruments.
Galileo's championing of heliocentrism was controversial
within his lifetime, when most subscribed to either geocentrism or the Tychonic
system.[9] He met with opposition from astronomers, who doubted heliocentrism
due to the absence of an observed stellar parallax.[9] The matter was
investigated by the Roman Inquisition in 1615, and they concluded that it could
be supported as only a possibility, not an established fact.[9][10] Galileo
later defended his views in Dialogue Concerning the Two Chief World Systems,
which appeared to attack Pope Urban VIII and thus alienated him and the
Jesuits, who had both supported Galileo up until this point.[9] He was tried by
the Inquisition, found "vehemently suspect of heresy", forced to
recant, and spent the rest of his life under house arrest.[11][12] It was while
Galileo was under house arrest that he wrote one of his finest works, Two New
Sciences, in which he summarised the work he had done some forty years earlier,
on the two sciences now called kinematics and strength of materials.[13][14]
Early life
Galileo was born in Pisa (then part of the Duchy of
Florence), Italy, the first of six children of Vincenzo Galilei, a famous
lutenist, composer, and music theorist; and Giulia Ammannati. Galileo became an
accomplished lutenist himself and would have learned early from his father a
healthy scepticism for established authority,[15] the value of well-measured or
quantified experimentation, an appreciation for a periodic or musical measure
of time or rhythm, as well as the illuminative progeny to expect from a
marriage of mathematics and experiment. Three of Galileo's five siblings
survived infancy, and 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 incapable of contributing
his fair share for 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 for support of his
musical endeavours and excursions. These financial burdens may have contributed
to Galileo's early fire to develop inventions that would bring him additional
income.
Galileo was named after an ancestor, Galileo Bonaiuti, a
physician, university teacher and politician who lived in Florence from 1370 to
1450; at that time in the late 14th century, the family's surname shifted from
Bonaiuti (or Buonaiuti) to Galilei. 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 buried too. When Galileo Galilei
was 8, his family moved to Florence, but he was left with Jacopo Borghini for
two years.[1] He then was educated in the Camaldolese Monastery at Vallombrosa,
35 km southeast of Florence.[1]
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.
Although a genuinely pious Roman Catholic,[16] Galileo
fathered three children out of wedlock with Marina Gamba. They had two
daughters, Virginia in 1600 and Livia in 1601, and one son, Vincenzo, 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.[17] 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.[18] 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 Bocchineri.[19]
Career as a scientist
Although he 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.[20] In 1581, when he was studying medicine, he noticed a
swinging chandelier, which air currents shifted about to swing in larger and
smaller arcs. 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 Christiaan Huygens almost one hundred
years later, however, that the tautochrone nature of a swinging pendulum was
used to create an accurate timepiece.[21] To this point, he had deliberately
been kept away from mathematics (since a physician earned so much more than a
mathematician), but upon accidentally attending a lecture on geometry, he
talked his reluctant father into letting him study mathematics and natural philosophy
instead.[21] He created a thermoscope (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
attained an instructor position 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.[22][23]
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, teaching
geometry, mechanics, and astronomy until 1610.[24] 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 improvement of 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.[25]
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".[26]
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.[27] The reference to tides was removed
by order of the Inquisition.
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 speeded 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.[28] 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.[29]
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.[30] Galileo dismissed the
idea, held by his contemporary Johannes Kepler, that the moon caused the tides,
[31] which the latter had acquired from the astrological tradition enunciated
in Ptolemy's Tetrabiblos.[citation needed] He also refused to accept Kepler's
elliptical orbits of the planets,[32] considering the circle the
"perfect" shape for planetary orbits.
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 had
published The Assayer (Il Saggiatore) in 1623, his last salvo in the dispute,
it had become a much wider argument over the very nature of science itself.
Because 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.[33]
Early in 1619, Father Grassi had anonymously published a pamphlet, An
Astronomical Disputation on the Three Comets of the Year 1618, [34] 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,[35]
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 the Comets,[36] 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.[37] Galileo and Guiducci
offered no definitive theory of their own on the nature of comets,[38] 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 Jesuit Christopher Scheiner,[39] and various uncomplimentary remarks about
the professors of the Collegio Romano were scattered throughout the work.[40]
The Jesuits were offended,[41] and Grassi soon replied with a polemical tract
of his own, The Astronomical and Philosophical Balance,[42] under the pseudonym
Lothario Sarsio Sigensano,[43] purporting to be one of his own pupils.
The Assayer was Galileo's devastating reply to the
Astronomical Balance.[44] It has been widely regarded as a masterpiece of
polemical literature,[45] in which "Sarsi's" arguments are subjected
to withering scorn.[46] It was greeted with wide acclaim, and particularly
pleased the new pope, Urban VIII, to whom it had been dedicated.[47] Galileo's
dispute with Grassi permanently alienated many of the Jesuits who had
previously been sympathetic to his ideas,[48] and Galileo and his friends were
convinced that these Jesuits were responsible for bringing about his later
condemnation.[49] The evidence for this is at best equivocal, however.[50]
Controversy over heliocentrism
Main article: Galileo affair
Cristiano Banti's 1857 painting Galileo facing the Roman
Inquisition
Biblical references Psalm 93:1, 96:10, and 1 Chronicles
16:30 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" etc.[51]
Galileo defended heliocentrism, and claimed it was not
contrary to those Scripture passages. He took Augustine's position on
Scripture: not to take every passage literally, particularly when the scripture
in question is a book of poetry and songs, not a book of instructions or
history. He believed that the writers of the Scripture merely wrote from the
perspective of the terrestrial world, from that vantage point that the sun does
rise and set. Another way to put this is that the writers would have been
writing from a phenomenological point of view, or style. So Galileo claimed
that science did not contradict Scripture, as Scripture was discussing a
different kind of "movement" of the earth, and not rotations.[52]
By 1616 the attacks on the ideas of Copernicus had reached a
head, and Galileo went to Rome to try to persuade the Catholic Church
authorities not to ban Copernicus' ideas. In the end, a decree of the Congregation
of the Index was issued, declaring that the ideas that the Sun stood still and
that the Earth moved were "false" and "altogether contrary to
Holy Scripture", and suspending Copernicus's De Revolutionibus until it
could be corrected. Acting on instructions from the Pope before the decree was
issued, Cardinal Bellarmine informed Galileo that it was forthcoming, that the
ideas it condemned could not be "defended or held", and ordered him
to abandon them. Galileo promised to obey. Bellarmine's instruction did not
prohibit Galileo from discussing heliocentrism as a mathematical fiction but
was dangerously ambiguous as to whether he could treat it as a physical
possibility.[53] For the next several years 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 Barberini as Pope Urban VIII in
1623. Barberini was a friend and admirer of Galileo, and had opposed the
condemnation of Galileo in 1616. The book, Dialogue Concerning the Two Chief
World Systems, was published in 1632, with formal authorization from the
Inquisition and papal permission.[54]
Dava Sobel[55] explains that during this time, Urban had
begun to fall more and more under the influence of court intrigue and problems
of state. His friendship with Galileo began to take second place to his
feelings of persecution and fear for his own life. At this low point in Urban's
life, the problem of Galileo was presented to the pope by court insiders and
enemies of Galileo. Coming on top of the recent claim by the then Spanish
cardinal that Urban was soft on defending the church, he reacted out of anger
and fear. This situation did not bode well for Galileo's defence of his book.
Earlier, 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".[56] 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.[57]
However, the Pope did not take the suspected public ridicule lightly, nor the
Copernican advocacy. 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, Galileo was ordered to come to Rome to
stand trial. He finally arrived in February 1633 and was brought before
inquisitor 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.[58] The sentence of the
Inquisition was delivered on June 22. 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.[59]
He was sentenced to formal imprisonment at the pleasure of
the Inquisition.[60] 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.[61]
Tomb of Galileo Galilei, Santa Croce
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, but there is no evidence that he actually said this or
anything similar. The first account of the legend dates to a century after his
death.[62]
After a period with the friendly Ascanio Piccolomini (the
Archbishop of Siena), Galileo was allowed to return to his villa at Arcetri
near 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.[63] 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. This book has received high praise from Albert
Einstein.[64] 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 travel to
Florence for medical advice.[13][14]
Death
Galileo continued to receive visitors until 1642, when,
after suffering fever and heart palpitations, he died on 8 January 1642, aged
77.[13] 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.[65] These plans
were scrapped, however, after Pope Urban VIII and his nephew, Cardinal
Francesco Barberini, protested,[66] because Galileo was condemned by the
Catholic Church for "vehement suspicion of heresy".[67] 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.[68] He was
reburied in the main body of the basilica in 1737 after a monument had been
erected there in his honour;[69] during this move, three fingers and a tooth
were removed from his remains.[70] One of these fingers, the middle finger from
Galileo's right hand, is currently on exhibition at the Museo Galileo in
Florence, Italy.[71]
Scientific methods
Galileo made original contributions to the science of motion
through an innovative combination of experiment and mathematics.[72] 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.[73] 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.[74]
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;...."[75] His mathematical analyses are a further
development of a tradition employed by late scholastic natural philosophers,
which Galileo learned when he studied philosophy.[76] He displayed a peculiar
ability to ignore established authorities, most notably Aristotelianism. In
broader terms, 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 reasoning.
Galileo showed a remarkably 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 friction and 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 Earth could not possibly be a parabola,[77] 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 only be very
slight.[78]
Astronomy
Fresco by Giuseppe Bertini depicting Galileo showing the
Doge of Venice how to use the telescope
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 description in
Sidereus Nuncius in March 1610
The phases of Venus, observed by Galileo in 1610
Based only on uncertain descriptions of the first practical
telescope which Hans Lippershey tried to patent in the Netherlands in 1608,[79]
Galileo, in the following year, made a telescope with about 3x magnification.
He later made improved versions with up to about 30x magnification.[80] 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 selling 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 treatise entitled Sidereus Nuncius (Starry Messenger).[81]
Kepler's Supernova
According to Walusinsky,[82] Galileo's fame as an astronomer
dates to his observation and discussion of Kepler's supernova in 1604. Since
this new star displayed no detectable diurnal parallax, Galileo concluded that
it was a distant star, and therefore disproved the Aristotelian belief in the
immutability of the heavens. His public advocacy of this view met with strong
opposition.[83]
Jupiter
On 7 January 1610 Galileo observed with his telescope what
he described at the time as "three fixed stars, totally invisible[84] by
their smallness", all close to Jupiter, and lying on a straight line
through it.[85] 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:[86] He had discovered three of Jupiter's four
largest satellites (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.[87]
Later astronomers, however, renamed them Galilean satellites in honour of their
discoverer. These satellites are now called Io, Europa, Ganymede, and Callisto.
His observations of the satellites of Jupiter created a
revolution in astronomy that reverberates to this day: 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,[88] and
many astronomers and philosophers initially refused to believe that Galileo
could have discovered such a thing.[89] His observations were confirmed by the
observatory of Christopher Clavius and he received a hero's welcome when he
visited Rome in 1611.[90] 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.[91]
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 Sun would 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
orbit of 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,[92] such as the Tychonic, Capellan and Extended Capellan models,[93]
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 geo-heliocentrism.
Galileo observed the planet Saturn, and at first mistook its
rings for planets, thinking it was a three-bodied system. When he observed the
planet later, 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 him.[94]
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.[95]
Sunspots
Galileo was one of the first Europeans to observe sunspots,
although Kepler had unwittingly observed one in 1607, but mistook it for a
transit of Mercury. He also reinterpreted a sunspot observation from the time
of Charlemagne, which formerly had been attributed (impossibly) to a transit of
Mercury. The very existence of sunspots showed another difficulty with the
unchanging perfection of the heavens posited by orthodox Aristotelian celestial
physics, but their regular periodic transits also confirmed the dramatic novel
prediction of Kepler's Aristotelian celestial dynamics in his 1609 Astronomia
Nova that the sun rotates, which was the first successful novel prediction of
post-spherist celestial physics.[96] And the annual variations in sunspots'
motions, discovered by Francesco Sizzi and others in 1612–1613,[97] provided a
powerful argument against both the Ptolemaic system and the geoheliocentric
system of Tycho Brahe.[98] A dispute over priority in the discovery of
sunspots, and in their interpretation, led Galileo to a long and bitter feud
with the Jesuit Christoph Scheiner; in fact, there is little doubt that both of
them were beaten by David Fabricius and his son Johannes, looking for
confirmation of Kepler's prediction of the sun's rotation. Scheiner quickly
adopted Kepler's 1615 proposal of the modern telescope design, which gave
larger magnification at the cost of inverted images; Galileo apparently never
changed to Kepler's design.
Moon
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[23] and the knowledge of chiaroscuro,[22] had
understood the patterns of light and shadow were in fact topological 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 topological 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
appeared to be clouds from Earth. 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.[99]
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.[100] 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.[101] 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.[102] 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.[103]
Technology
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 technology, as distinct from pure physics. This is not the same distinction
as made by Aristotle, who would have considered all Galileo's physics as techne
or useful knowledge, as opposed to episteme, or philosophical investigation
into the causes of things. 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 designed by 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 maker 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.[104]
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,[105] at a
banquet held in 1611 by Prince Federico Cesi to make Galileo a member of his
Accademia dei Lincei.[106] 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.[107] By 1624 Galileo had perfected[108] a
compound microscope. He gave one of these instruments to Cardinal Zollern in
May of that year for presentation to the Duke of Bavaria,[109] and in September
he sent another to Prince Cesi.[110] 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".[111][112] 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.[113]
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 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.[114] In his last year, when totally blind, he designed an escapement
mechanism for a pendulum clock (called Galileo's escapement), a vectorial model
of which may be seen here. The first fully operational pendulum clock was made
by Christiaan Huygens in the 1650s.
Physics
Galileo e Viviani, 1892, Tito Lessi
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,[115] as was discovered by Christian 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
Technology above.)
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.[116] Sometime between
Galileo's death and 1667, the members of the Florentine Accademia del Cimento
repeated the experiment over a distance of about a mile and obtained a
similarly inconclusive result.[117] 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 and is central to
Einstein's special theory of relativity.
Falling bodies
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.[118] This was contrary to what Aristotle had taught: that heavy objects
fall faster than lighter ones, in direct proportion to weight.[119] 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.[120] An
exception is Drake,[121] 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),[21] although the building used
was actually the church tower in Delft in 1586.[122]
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[123] and Simon Stevin.[124] 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.[125] 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
).[126] However, in neither case were these discoveries entirely original. The
time-squared law for uniformly accelerated change was already known to Nicole
Oresme in the 14th century,[127] and Domingo de Soto, in the 16th, had
suggested that bodies falling through a homogeneous medium would be uniformly
accelerated.[128] 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 unless a force—often
friction—acts upon them, refuting the generally accepted Aristotelian
hypothesis that objects "naturally" slow down and stop unless a force
acts upon them (philosophical ideas relating to inertia had been proposed by
John Philoponus centuries earlier, as had Jean Buridan, and according to Joseph
Needham, Mo Tzu had proposed it centuries before either of them, but this was
the first time that it had been mathematically expressed, verified
experimentally, and introduced the idea of frictional force, the key
breakthrough in validating inertia). Galileo's Principle of Inertia stated:
"A body moving on a level surface will continue in the same direction at
constant speed unless disturbed." This principle was incorporated into
Newton's laws of motion (first law).
Dome of the Cathedral of Pisa with the "lamp of
Galileo"
Mathematics
While Galileo's application of mathematics to experimental
physics was innovative, his mathematical methods were the standard ones of the
day. 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.
Galileo produced some mathematics: Galileo's paradox, which
shows that there are as many perfect squares as there are whole numbers, even
though most numbers are not perfect squares.
His writings
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[129] and the 1606 printed
manual Le Operazioni del Compasso Geometrico et Militare on the operation of a
geometrical and military compass.[130]
His early works in dynamics, the science of motion and
mechanics were his 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 Hipparchan-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 acceleration.
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;
and
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[131] suggesting the Sun and heavens are corruptible. The
Letters on Sunspots also reported his 1610 telescopic observations of the full
set of phases of Venus, and his discovery of the puzzling
"appendages" of 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.[132] 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.[133] 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.[134]
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.[135] 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 Inquisition.
Summary of Galileo's Published Written Works
Galileo's main written works are as follows:
The Little Balance (1586)
On Motion (1590)[136]
Mechanics (ca. 1600)
The Starry Messenger (1610; in Latin, Sidereus Nuncius)
Discourse on Floating Bodies (1612)
Letters on Sunspots (1613)
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 (1632; in
Italian Dialogo dei 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)
Legacy
Church reassessments of Galileo in later centuries
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.[137] In 1741 Pope Benedict XIV
authorised the publication of an edition of Galileo's complete scientific
works[138] which included a mildly censored version of the Dialogue.[139] 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.[140] All traces of
official opposition to heliocentrism by the church disappeared in 1835 when
these works were finally dropped from the Index.[141]
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".[142] 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."[143]
On 15 February 1990, in a speech delivered at the Sapienza
University of Rome,[144] Cardinal Ratzinger (later to become 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".[145] 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."[145] 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."[145]
On 31 October 1992, 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.[146][147] 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.[148] In December
of the same year, during events to mark the 400th anniversary of Galileo's
earliest telescopic observations, Pope Benedict XVI praised his contributions
to astronomy.[149] 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 suspended.[150]
Impact on modern science
According to Stephen Hawking, Galileo probably bears more of
the responsibility for the birth of modern science than anybody else,[151] and
Albert Einstein called him the father of modern science.[152][153]
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,[154] the first spacecraft to enter orbit around Jupiter, the
proposed Galileo global satellite navigation system, the transformation between
inertial systems in classical mechanics denoted Galilean transformation and the
Gal (unit), sometimes known as the Galileo which is a non-SI unit of
acceleration.
International Year of Astronomy commemorative coin
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.[155] 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 of 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.
Asteroid 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".[156] He features
prominently in the song "Galileo" performed by the Indigo Girls.
Twentieth-century plays have been written on Galileo's life,
including Life of Galileo (1943) by the German playwright Bertolt Brecht, with
a film adaptation (1975) of it, and Lamp At Midnight (1947) by Barrie
Stavis,[157] as well as the 2008 play "Galileo Galilei".[158]
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.[159]
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 Galileoscope was also released. This is a mass-produced, low-cost
educational 2-inch (51 mm) telescope with relatively high quality.
Timeline
1543 – 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
~1570 – Thomas Digges publishes Pantometria describing a
telescope built between 1540–1559 by his father Leonard Digges
1573 – 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[160]
1581 – His father, Vincenzo Galilei publishes Dialogo della
musica antica et moderna formulating musical theories[161]
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 balance)
1586 – Simon Stevin publishes results for dropping lead
weights from 10 meters
1588 – Tycho Brahe publishes work on comets containing a
description of the Tychonic system of the world[162]
1589 – Appointed to Mathematics Chair, University of Pisa
1590 – Partially completes De Motu (On Motion), which is
never published
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 System
1600 – First child, Virginia is born; ~1600 Le Meccaniche
(Mechanics)
1600 – William Gilbert publishes On the Magnet and Magnetic
Bodies, and on That Great Magnet the Earth with arguments supporting the
Copernican system
1600 – 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 new star
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
1608 – 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
1609 – 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[163]
1610 – Lifetime appointment to mathematics position at
University of Padua, and as mathematician and philosopher for Cosimo II, Grand
Duke of Tuscany
1611 – Discovers phases of Venus; granted audience with
Pope; made member of Lincean Academy
1611 – 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 sunspots' motions
1613 – Letters on Sunspots
1615 – Letter to Grand Duchess Christina (not published
until 1636)
1616 – Officially warned by the Church not to hold or defend
the Copernican System
1616 – The Catholic Church places De revolutionibus orbium
coelestium on the List of Prohibited Books
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 law
1619 – Discourse on the Comets
1621 – 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
microscopes published
1630 – Completes Dialogue Concerning the Two Chief World
Systems and subsequently receives approval of Church censor
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
1633 – 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
1668 – Newton builds his reflecting telescope
1687 – Isaac Newton publishes Philosophiæ Naturalis
Principia Mathematica deriving Kepler's laws from the Universal Law of
Gravitation and the Laws of Motion, uniting the heavens and earth under the
same natural laws
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