Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian
astronomer,
physicist and
engineer, sometimes described as a
polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was born in the city of
Pisa
Pisa ( , or ) is a city and ''comune'' in Tuscany, central Italy, straddling the Arno just before it empties into the Ligurian Sea. It is the capital city of the Province of Pisa. Although Pisa is known worldwide for its leaning tower, the cit ...
, then part of the
Duchy of Florence
The Duchy of Florence ( it, Ducato di Firenze) was an Italian principality that was centred on the city of Florence, in Tuscany, Italy. The duchy was founded after Emperor Charles V restored Medici rule to Florence in 1530. Pope Clement VII, himse ...
. Galileo has been called the "father" of
observational astronomy, modern physics,
the
scientific method, and
modern science
The history of science covers the development of science from ancient history, ancient times to the present. It encompasses all three major branches of science: natural science, natural, social science, social, and formal science, formal.
Sc ...
.
Galileo studied
speed and
velocity,
gravity and
free fall, the
principle of relativity
In physics, the principle of relativity is the requirement that the equations describing the laws of physics have the same form in all admissible frames of reference.
For example, in the framework of special relativity the Maxwell equations have ...
,
inertia,
projectile motion and also worked in applied science and technology, describing the properties of
pendulums and "
hydrostatic
Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...
balances". He invented the
thermoscope and various
military compasses, and used the
telescope for scientific observations of celestial objects. His contributions to observational astronomy include telescopic confirmation of the
phases of Venus, observation of the
four largest satellites of
Jupiter, observation of
Saturn's rings, and analysis of
lunar craters and
sunspots
Sunspots are phenomena on the Sun's photosphere that appear as temporary spots that are darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. ...
.
Galileo's championing of
Copernican heliocentrism (Earth rotating daily and revolving around the Sun) was met with opposition from within the
Catholic Church and from some astronomers. The matter was investigated by the
Roman Inquisition in 1615, which concluded that heliocentrism was foolish, absurd, and heretical since it contradicted 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 ( la, Urbanus VIII; it, Urbano VIII; baptised 5 April 1568 – 29 July 1644), born Maffeo Vincenzo Barberini, was head of the Catholic Church and ruler of the Papal States from 6 August 1623 to his death in July 1644. As po ...
and thus alienated both the Pope 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. During this time, he wrote ''
Two New Sciences'' (1638), primarily concerning
kinematics
Kinematics is a subfield of physics, developed in classical mechanics, that describes the Motion (physics), motion of points, Physical object, bodies (objects), and systems of bodies (groups of objects) without considering the forces that cause ...
and the
strength of materials, summarizing work he had done around forty years earlier.
Early life and family
Galileo was born in
Pisa
Pisa ( , or ) is a city and ''comune'' in Tuscany, central Italy, straddling the Arno just before it empties into the Ligurian Sea. It is the capital city of the Province of Pisa. Although Pisa is known worldwide for its leaning tower, the cit ...
(then part of the
Duchy of Florence
The Duchy of Florence ( it, Ducato di Firenze) was an Italian principality that was centred on the city of Florence, in Tuscany, Italy. The duchy was founded after Emperor Charles V restored Medici rule to Florence in 1530. Pope Clement VII, himse ...
), Italy, on 15 February 1564,
the first of six children of
Vincenzo Galilei, a
lutenist
A lute ( or ) is any plucked string instrument with a neck and a deep round back enclosing a hollow cavity, usually with a sound hole or opening in the body. It may be either fretted or unfretted.
More specifically, the term "lute" can refe ...
, composer, and
music theorist, and
Giulia 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.
Three of Galileo's five siblings survived infancy. The youngest,
Michelangelo
Michelangelo di Lodovico Buonarroti Simoni (; 6 March 1475 – 18 February 1564), known as Michelangelo (), was an Italian sculptor, painter, architect, and poet of the High Renaissance. Born in the Republic of Florence, his work was insp ...
(or Michelagnolo), also became a lutenist and composer who added to Galileo's financial burdens for the rest of his life. 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.
When Galileo Galilei was eight, his family moved to
Florence, but he was left under the care of Muzio Tedaldi for two years. When Galileo was ten, he left Pisa to join his family in Florence and there he was under the tutelage of Jacopo Borghini.
He was educated, particularly in logic, from 1575 to 1578 in the
Vallombrosa Abbey
Vallombrosa is a Benedictine abbey in the ''comune'' of Reggello (Tuscany, Italy), about 30 km south-east of Florence, in the Apennines, surrounded by forests of beech and firs. It was founded by Florentine nobleman Giovanni Gualberto in 10 ...
, about 30 km southeast of Florence.
Name
Galileo tended to refer to himself only by his given name. At the time, surnames were optional in Italy, and his given name had the same origin as his sometimes-family name, Galilei. Both his given and family name ultimately derive from an ancestor,
Galileo Bonaiuti, an important physician, professor, and politician in Florence in the 15th century. Galileo Bonaiuti was buried in the same church, the
Basilica of Santa Croce in Florence, where about 200 years later, Galileo Galilei was also buried.
When he did refer to himself with more than one name, it was sometimes as Galileo Galilei Linceo, a reference to his being a member of the
Accademia dei Lincei
The Accademia dei Lincei (; literally the "Academy of the Lynx-Eyed", but anglicised as the Lincean Academy) is one of the oldest and most prestigious European scientific institutions, located at the Palazzo Corsini on the Via della Lungara in Rom ...
, an elite pro-science organization in Italy. 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
Galilee (; he, הַגָּלִיל, hagGālīl; ar, الجليل, al-jalīl) is a region located in northern Israel and southern Lebanon. Galilee traditionally refers to the mountainous part, divided into Upper Galilee (, ; , ) and Lower Galil ...
", a biblically significant region in Northern
Israel. Because of that region, the adjective ''galilaios'' (
Greek Γαλιλαῖος,
Latin ''Galilaeus'',
Italian ''Galileo''), which means "Galilean", was used in antiquity (particularly by
emperor Julian) to refer to
Christ and
his followers.
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
The Acts of the Apostles ( grc-koi, Πράξεις Ἀποστόλων, ''Práxeis Apostólōn''; la, Actūs Apostolōrum) is the fifth book of the New Testament; it tells of the founding of the Christian Church and the spread of its message ...
, "Ye men of Galilee, why stand ye gazing up into heaven?" (in the
Latin version found in the
Vulgate: ''Viri Galilaei, quid statis aspicientes in caelum?'').
Children
Despite being a genuinely pious Roman Catholic, Galileo fathered three children out of wedlock with
Marina Gamba
Marina Gamba of Venice ( – ) was the mother of Galileo Galilei's illegitimate children.
Marina Gamba was born around 1570 in Venice.
Relationship with Galileo Galilei
During one of his frequent trips to Venice, Galileo met a young woman named ...
. They had two daughters, Virginia (born 1600) and Livia (born 1601), and a son,
Vincenzo
Vincenzo is an Italian male given name, derived from the Latin name Vincentius (the verb ''vincere'' means to win or to conquer). Notable people with the name include:
Art
* Vincenzo Amato (born 1966), Italian actor and sculptor
*Vincenzo Bell ...
(born 1606).
Due to their illegitimate birth, Galileo 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
Arcetri is a location in Florence, Italy, positioned among the hills south of the city centre.
__TOC__
Landmarks
A number of historic buildings are situated there, including the house of the famous scientist Galileo Galilei (called ''Villa Il Gio ...
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
The (Italian for 'Basilica of the Holy Cross') is the principal Franciscan church in Florence, Italy, and a minor basilica of the Roman Catholic Church. It is situated on the Piazza di Santa Croce, about 800 meters south-east of the Duomo. The ...
. Livia took the name Sister Arcangela and was ill for most of her life. Vincenzo was later
legitimised
Legitimation or legitimisation is the act of providing legitimacy. Legitimation in the social sciences refers to the process whereby an act, process, or ideology becomes legitimate by its attachment to norms and values within a given society. It ...
as the legal heir of Galileo and married Sestilia Bocchineri.
Career as a scientist
Although Galileo seriously considered the priesthood as a young man, at his father's urging he instead enrolled in 1580 at the
University of Pisa for a medical degree. He was influenced by the lectures of
Girolamo Borro
Girolamo Borro (1512 – 26 August 1592) latinized as Hieronomyus Borrius was an Italian philosopher and a professor at the University of Pisa. He belonged to a group of natural philosophers who rejected appeals to the supernatural and occult to e ...
and Francesco Buonamici of Florence.
In 1581, when he was studying medicine, he noticed a swinging
chandelier
A chandelier (; also known as girandole, candelabra lamp, or least commonly suspended lights) is a branched ornamental light fixture designed to be mounted on ceilings or walls. Chandeliers are often ornate, and normally use incandescent li ...
, 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
Christiaan Huygens, Lord of Zeelhem, ( , , ; also spelled Huyghens; la, Hugenius; 14 April 1629 – 8 July 1695) was a Dutch mathematician, physicist, engineer, astronomer, and inventor, who is regarded as one of the greatest scientists of ...
, almost one hundred years later, that the
tautochrone nature of a swinging pendulum was used to create an accurate timepiece.
[Asimov, Isaac (1964). ''Asimov's Biographical Encyclopedia of Science and Technology''. ] 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
Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...
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
The Accademia delle Arti del Disegno ("Academy of the Arts of Drawing") is an academy of artists in Florence, Italy. Founded as Accademia e Compagnia delle Arti del Disegno ("Academy and Company of the Arts of Drawing") on 13 January 1563 by ...
in Florence, teaching perspective and
chiaroscuro. In the same year, upon invitation by the
Florentine Academy
The Accademia di Belle Arti di Firenze ("academy of fine arts of Florence") is an instructional art academy in Florence, in Tuscany, in central Italy.
It was founded by Cosimo I de' Medici in 1563, under the influence of Giorgio Vasari. M ...
, he presented two lectures, ''
On the Shape, Location, and Size of Dante's Inferno
''On the Shape, Location, and Size of Dante's Inferno'' is the title of two lectures by Galileo Galilei presented in 1588 upon invitation by the Florentine Academy. The lectures secured him a job as a lecturer of mathematics at the University of Pi ...
'', in an attempt to propose a rigorous cosmological model of
Dante's hell
''Inferno'' (; Italian for "Hell") is the first part of Italian writer Dante Alighieri's 14th-century epic poem ''Divine Comedy''. It is followed by '' Purgatorio'' and '' Paradiso''. The ''Inferno'' describes Dante's journey through Hell, g ...
. 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.
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
Kinematics is a subfield of physics, developed in classical mechanics, that describes the Motion (physics), motion of points, Physical object, bodies (objects), and systems of bodies (groups of objects) without considering the forces that cause ...
of motion and astronomy) as well as practical
applied science
Applied science is the use of the scientific method and knowledge obtained via conclusions from the method to attain practical goals. It includes a broad range of disciplines such as engineering and medicine. Applied science is often contrasted ...
(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.
Astronomy
Kepler's supernova
Tycho Brahe and others had observed the
supernova of 1572
SN 1572 ('' Tycho's Supernova'', ''Tycho's Nova''), or B Cassiopeiae (B Cas), was a supernova of Type Ia in the constellation Cassiopeia, one of eight supernovae visible to the naked eye in historical records. It appeared in early November 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.
Refracting telescope
![Galileo galilei, telescopi del 1609-10 ca](https://upload.wikimedia.org/wikipedia/commons/d/d7/Galileo_galilei%2C_telescopi_del_1609-10_ca..JPG)
Based only on uncertain descriptions of the first practical telescope which
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
A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses and as ...
, 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
Venetian often means from or related to:
* Venice, a city in Italy
* Veneto, a region of Italy
* Republic of Venice (697–1797), a historical nation in that area
Venetian and the like may also refer to:
* Venetian language, a Romance language s ...
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
treatise entitled ''
Sidereus Nuncius'' (''Starry Messenger'').
Moon
On 30 November 1609, Galileo aimed his telescope at the
Moon. While not being the first person to observe the Moon through a telescope (English mathematician
Thomas Harriot had done it four months before but only saw a "strange spottednesse"), 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. Galileo is sometimes credited with the discovery of the
lunar libration in latitude in 1632, although Thomas Harriot or
William Gilbert might have done it before.
A friend of Galileo's, the painter Cigoli, included a realistic depiction of the Moon in one of his paintings, though probably used his own telescope to make the observation.
Jupiter's moons
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
In astronomy, fixed stars ( la, stellae fixae) is a term to name the full set of glowing points, astronomical objects actually and mainly stars, that appear not to move relative to one another against the darkness of the night sky in the backgro ...
. 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 were independently discovered by
Simon Marius on 8 January 1610 and are now called
Io,
Europa
Europa may refer to:
Places
* Europe
* Europa (Roman province), a province within the Diocese of Thrace
* Europa (Seville Metro), Seville, Spain; a station on the Seville Metro
* Europa City, Paris, France; a planned development
* Europa Cliff ...
,
Ganymede, and
Callisto, the names given by Marius in his ''Mundus Iovialis'' published in 1614.
Galileo's 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 observatory of
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
Johannes Kepler
Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws ...
had believed impossible.
Phases of Venus
![Phases-of-Venus](https://upload.wikimedia.org/wikipedia/commons/d/d1/Phases-of-Venus.svg)
From September 1610, Galileo observed that
Venus exhibits
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. 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 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, the Ptolemaic model became untenable. 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 explained the phases of Venus without the 'refutation' of full heliocentrism's prediction of stellar parallax. Galileo's discovery of the phases of Venus was thus his most empirically practically influential contribution to the two-stage transition from full geocentrism to full heliocentrism via geo-heliocentrism.
Saturn and Neptune
In 1610, Galileo also observed the planet
Saturn
Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
, 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.
Galileo observed the planet
Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
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.
Sunspots
Galileo made naked-eye and telescopic studies of
sunspot
Sunspots are phenomena on the Sun's photosphere that appear as temporary spots that are darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sun ...
s.
[ 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"] 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
, image = Ihs-logo.svg
, image_size = 175px
, caption = ChristogramOfficial seal of the Jesuits
, abbreviation = SJ
, nickname = Jesuits
, formation =
, founders ...
Christoph Scheiner. In the middle was
Mark Welser
Mark Welser (1558–1614) was a German banker, politician, and astronomer, who engaged in learned correspondence with European intellectuals of his time. Of particular note is his exchange with Galileo Galilei, regarding sunspots.
Biography
We ...
, to whom Scheiner had announced his discovery, and who asked Galileo for his opinion. Both of them were unaware of
Johannes Fabricius' earlier observation and publication of sunspots.
Milky Way and stars
Galileo observed the
Milky Way, previously believed to be
nebulous
''Nebulous'' is a post-apocalyptic science fiction comedy radio show written by Graham Duff and produced by Ted Dowd from Baby Cow Productions; it is directed by Nicholas Briggs. The series premiered in the United Kingdom on BBC Radio 4. Set ...
, and found it to be a multitude of stars packed so densely that they appeared from 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
'' Letters on Sunspots '' (''Istoria e Dimostrazioni intorno alle Macchie Solari'') was a pamphlet written by Galileo Galilei in 1612 and published in Rome by the Accademia dei Lincei in 1613. In it, Galileo outlined his recent observation of dark ...
'', 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
arcsecond
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
s, 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, 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 Brahe, 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
Martin (Maarten) van den Hove (Latinized as Martinus Hortensius (Ortensius)) (1605 – 7 August 1639) was a Dutch astronomer and mathematician. His adopted Latin name is a translation of the Dutch ''hof'' ("garden"), in Latin ''horta''.
Early li ...
made similar measurements of stars, and Marius and Riccioli concluded the smaller sizes were not small enough to answer Tycho's argument.
Theory of tides
Cardinal Bellarmine
Robert Bellarmine, SJ ( it, Roberto Francesco Romolo Bellarmino; 4 October 1542 – 17 September 1621) was an Italian Jesuit and a cardinal of the Catholic Church. He was canonized a saint in 1930 and named Doctor of the Church, one of only ...
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 such evidence. This theory was so important to him that he originally intended to call his ''Dialogue Concerning 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 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 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
Venice ( ; it, Venezia ; vec, Venesia or ) is a city in northeastern Italy and the capital of the Veneto Regions of Italy, region. It is built on a group of 118 small islands that are separated by canals and linked by over 400 ...
instead of one, about 12 hours apart. Galileo dismissed this anomaly as the result of several secondary causes including the shape of the sea, its depth, and other factors.
Albert Einstein later 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 also dismissed the idea,
known from antiquity and by his contemporary Johannes Kepler, that the
Moon caused the tides—Galileo also took no interest in Kepler's
elliptical orbits of the planets. Galileo continued to argue in favour of his theory of tides, considering it the ultimate proof of Earth's motion.
Controversy over comets and ''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
''The Assayer'' ( it, Il Saggiatore) was a book published in Rome by Galileo Galilei in October 1623 and is generally considered to be one of the pioneering works of the scientific method, first broaching the idea that the book of nature is to be ...
'' (''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.
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. 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 that 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. (The correct approach to the study of comets had been proposed at the time by Tycho Brahe.) In its opening passage, Galileo and Guiducci's ''Discourse'' gratuitously insulted the Jesuit
Christoph Scheiner, and various uncomplimentary remarks about the professors of the
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 Academy.
Galileo's dispute with Grassi permanently alienated many Jesuits, and Galileo and his friends were convinced that they were responsible for bringing about his later condemnation, although supporting evidence for this is not conclusive.
Controversy over heliocentrism
![Galileo facing the Roman Inquisition](https://upload.wikimedia.org/wikipedia/commons/8/88/Galileo_facing_the_Roman_Inquisition.jpg)
At the time of Galileo's conflict with the Church, the majority of educated people subscribed to the
Aristotelian geocentric view that the Earth is the
center of the Universe and the orbit of all heavenly bodies, or Tycho Brahe's new system blending geocentrism with heliocentrism. Opposition to heliocentrism and Galileo's writings on it combined religious and scientific objections. Religious opposition to heliocentrism arose from biblical passages implying the fixed nature of the Earth. Scientific opposition came from Brahe, who argued that if heliocentrism were true, an annual stellar parallax should be observed, though none was at the time. Aristarchus and Copernicus had correctly postulated that parallax was negligible because the stars were so distant. However, Tycho countered that since stars
appear to have measurable angular size, if the stars were that distant and their apparent size is due to their physical size, they would be far larger than the Sun. In fact,
it is not possible to observe the physical size of distant stars without modern telescopes.
Galileo defended heliocentrism based on
his astronomical observations of 1609. In December 1613, the Grand Duchess
Christina of Florence confronted one of Galileo's friends and followers,
Benedetto Castelli, with biblical objections to the motion of the Earth. 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 science. This letter was not published, but circulated widely. Two years later, Galileo wrote a
letter to Christina that expanded his arguments previously made in eight pages to forty pages.
By 1615, Galileo's writings on heliocentrism had been submitted to the
Roman Inquisition by Father
Niccolò Lorini Niccolò Lorini was born in Florence in 1544. He served as a Preacher General Dominican Order and a lecturer in ecclesiastical history at the University of Florence. He is most famous for his involvement in the Galileo trails, the Galileo affair. H ...
, who claimed that Galileo and his followers were attempting to reinterpret the Bible, which was seen as a violation of the
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 ideas. At the start of 1616, Monsignor
Francesco Ingoli
Francesco Ingoli (21 November 1578 – 24 April 1649) was an Italian Catholic priest, lawyer and professor of civil and canon law.
Early life
Born in Ravenna Italy, Ingoli learned a number of languages, including Arabic, and graduated from t ...
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. Ingoli may have been commissioned by the Inquisition to write an expert opinion on the controversy, with the essay providing the basis for the Inquisition's actions. The essay focused on eighteen physical and mathematical arguments against heliocentrism. It borrowed primarily from Tycho Brahe's arguments, notably that heliocentrism would require the stars as they appeared to be much larger than the Sun. 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".
Pope Paul V instructed Cardinal Bellarmine to deliver this finding to Galileo, and to order him to abandon heliocentrism. 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 writing." The decree of the
Congregation of the Index
The ''Index Librorum Prohibitorum'' ("List of Prohibited Books") was a list of publications deemed heretical or contrary to morality by the Sacred Congregation of the Index (a former Dicastery of the Roman Curia), and Catholics were forbidde ...
banned Copernicus's ''De Revolutionibus'' and other heliocentric works until correction.
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
Barberini as
Pope Urban VIII
Pope Urban VIII ( la, Urbanus VIII; it, Urbano VIII; baptised 5 April 1568 – 29 July 1644), born Maffeo Vincenzo Barberini, was head of the Catholic Church and ruler of the Papal States from 6 August 1623 to his death in July 1644. As po ...
in 1623. Barberini was a friend and admirer of Galileo, and had opposed the admonition 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.
![Galileo-sustermans4](https://upload.wikimedia.org/wikipedia/commons/5/5d/Galileo-sustermans4.jpg)
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. 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.
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 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. 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.
The sentence of the Inquisition was delivered on 22 June. It was in three essential parts:
* Galileo was found "vehemently suspect of heresy" (though he was never formally charged with heresy, relieving him of facing corporal punishment), 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
Abjuration is the solemn repudiation, abandonment, or renunciation by or upon oath, often the renunciation of citizenship or some other right or privilege. The term comes from the Latin ''abjurare'', "to forswear".
Abjuration of the realm
Abj ...
, 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, under which he remained 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.
![E pur si muove](https://upload.wikimedia.org/wikipedia/commons/0/06/E_pur_si_muove.jpg)
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
''And Yet It Moves'' is a puzzle-platform game developed by Independent video game development, independent developer Broken Rules. The game was released for Microsoft Windows, Mac OS X, and Linux on April 2, 2009, and for Wii as a WiiWare titl ...
". There was a claim that a 1640s painting by the Spanish painter
Bartolomé Esteban Murillo
Bartolomé Esteban Murillo ( , ; late December 1617, baptized January 1, 1618April 3, 1682) was a Spanish Baroque painter. Although he is best known for his religious works, Murillo also produced a considerable number of paintings of contemporar ...
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. Based on the painting,
Stillman Drake wrote "there is no doubt now that the famous words were already attributed to Galileo before his death". However, an intensive investigation by astrophysicist
Mario Livio
Mario Livio (born June 19, 1945) is an Israeli-American astrophysicist and an author of works that popularize science and mathematics. For 24 years (1991-2015) he was an astrophysicist at the Space Telescope Science Institute, which operates th ...
has revealed that said painting is most probably a copy of a 1837 painting by the Flemish painter Roman-Eugene Van Maldeghem.
After a period with the friendly
Ascanio Piccolomini (the Archbishop of
Siena), Galileo was allowed to return to his villa at
Arcetri
Arcetri is a location in Florence, Italy, positioned among the hills south of the city centre.
__TOC__
Landmarks
A number of historic buildings are situated there, including the house of the famous scientist Galileo Galilei (called ''Villa Il Gio ...
near Florence in 1634, where he spent part of his life under house arrest. Galileo was ordered to read the
Seven Penitential Psalms
The Penitential Psalms or Psalms of Confession, so named in Cassiodorus's commentary of the 6th century AD, are the Psalms 6, 31, 37, 50, 101, 129, and 142 (6, 32, 38, 51, 102, 130, and 143 in the Hebrew numbering).
*Psalm 6 – Domine, ne i ...
once a week for the next three years. However, his daughter Maria Celeste relieved him of the burden after securing