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Galileo Galilei

Galileo Galilei

Overview
Galileo Galilei was an Italian physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...

, mathematician
Mathematician
A mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....

, astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

, and philosopher who played a major role in the Scientific Revolution
Scientific revolution
The Scientific Revolution is an era associated primarily with the 16th and 17th centuries during which new ideas and knowledge in physics, astronomy, biology, medicine and chemistry transformed medieval and ancient views of nature and laid the foundations for modern science...

. His achievements include improvements to the telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

 and consequent astronomical observations and support for Copernicanism
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....

. Galileo has been called the "father of modern observational astronomy
Observational astronomy
Observational astronomy is a division of the astronomical science that is concerned with getting data, in contrast with theoretical astrophysics which is mainly concerned with finding out the measurable implications of physical models...

", the "father of modern physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

", the "father of science", and "the Father of Modern Science".

His contributions to observational astronomy include the telescopic confirmation of the phases of Venus
Phases of Venus
The phases of the planet Venus are the different variations of lighting seen on the planet's surface, similar to lunar phases. The first recorded observations of them were telescopic observations by Galileo Galilei in 1610...

, the discovery of the four largest satellites of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

 (named the Galilean moons
Galilean moons
The Galilean moons are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance...

 in his honour), and the observation and analysis of sunspots.
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Timeline

1609   Galileo Galilei demonstrates his first telescope to Venetian lawmakers.

1610   Galileo Galilei observes three of the four largest moons of Jupiter for the first time. He named them, and in turn the four are called the Galilean moons. Ganymede not discovered by him until January 13.

1610   Galileo Galilei discovers Ganymede, 4th moon of Jupiter.

1612   Galileo Galilei becomes the first astronomer to observe the planet Neptune, although he mistakenly catalogued it as a fixed star.

1632   Galileo's ''Dialogue Concerning the Two Chief World Systems'' is published.

1633   Galileo Galilei arrives in Rome for his trial before the Inquisition.

1633   The formal inquest of Galileo Galilei by the Inquisition begins.

1633   The Holy Office in Rome forces Galileo Galilei to recant his view that the Sun, not the Earth, is the center of the Universe.

1633   Galileo Galilei is tried before the Congregation for the Doctrine of the Faith for teaching that the Earth orbits the Sun.

 
Quotations

What has philosophy got to do with measuring anything? It's the mathematicians you have to trust, and they measure the skies like we measure a field.

"Matteo" in Concerning the New Star (1606)

My dear Kepler, what would you say of the learned here, who, replete with the pertinacity of the asp, have steadfastly refused to cast a glance through the telescope? What shall we make of this? Shall we laugh, or shall we cry?

Letter to Johannes Kepler (1610), as quoted in The Crime of Galileo (1955) by Giorgio De Santillana

See now the power of truth; the same experiment which at first glance seemed to show one thing, when more carefully examined, assures us of the contrary.

Discourses and Mathematical Demonstrations Relating to Two New Sciences (1638); Discorsi e dimostrazioni matematiche, intorno à due nuove scienze, as translated by Henry Crew and Alfonso de Salvio (1914)

You cannot teach a man anything, you can only help him to find it within himself.

As quoted in How to Win Friends and Influence People (1935) by Dale Carnegie, p. 117; also paraphrased as "You cannot teach a man anything, you can only help him to find it for himself."

I have never met a man so ignorant that I could not learn something from him.

As quoted in The Story of Civilization : The Age of Reason Begins, 1558-1648 (1935) by Will Durant, p. 605
Encyclopedia
Galileo Galilei was an Italian physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...

, mathematician
Mathematician
A mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....

, astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

, and philosopher who played a major role in the Scientific Revolution
Scientific revolution
The Scientific Revolution is an era associated primarily with the 16th and 17th centuries during which new ideas and knowledge in physics, astronomy, biology, medicine and chemistry transformed medieval and ancient views of nature and laid the foundations for modern science...

. His achievements include improvements to the telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

 and consequent astronomical observations and support for Copernicanism
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....

. Galileo has been called the "father of modern observational astronomy
Observational astronomy
Observational astronomy is a division of the astronomical science that is concerned with getting data, in contrast with theoretical astrophysics which is mainly concerned with finding out the measurable implications of physical models...

", the "father of modern physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

", the "father of science", and "the Father of Modern Science".

His contributions to observational astronomy include the telescopic confirmation of the phases of Venus
Phases of Venus
The phases of the planet Venus are the different variations of lighting seen on the planet's surface, similar to lunar phases. The first recorded observations of them were telescopic observations by Galileo Galilei in 1610...

, the discovery of the four largest satellites of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

 (named the Galilean moons
Galilean moons
The Galilean moons are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance...

 in his honour), and the observation and analysis of sunspots. Galileo also worked in applied science and technology, inventing an improved military compass
Sector (instrument)
The sector, also known as a proportional compass or military compass, was a major calculating instrument in use from the end of the sixteenth century until the nineteenth century. It is an instrument consisting of two rulers of equal length which are joined by a hinge. A number of scales are...

 and other instruments.

Galileo's championing of heliocentrism
Heliocentrism
Heliocentrism, or heliocentricism, is the astronomical model in which the Earth and planets revolve around a stationary Sun at the center of the universe. The word comes from the Greek . Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center...

 was controversial within his lifetime, when most subscribed to either geocentrism or the Tychonic system
Tychonic system
The Tychonic system was a model of the solar system published by Tycho Brahe in the late 16th century which combined what he saw as the mathematical benefits of the Copernican system with the philosophical and "physical" benefits of the Ptolemaic system...

. He met with opposition from astronomers, who doubted heliocentrism due to the absence of an observed stellar parallax
Stellar parallax
Stellar parallax is the effect of parallax on distant stars in astronomy. It is parallax on an interstellar scale, and it can be used to determine the distance of Earth to another star directly with accurate astrometry...

. The matter was investigated by the Roman Inquisition
Roman Inquisition
The Roman Inquisition was a system of tribunals developed by the Holy See during the second half of the 16th century, responsible for prosecuting individuals accused of a wide array of crimes related to heresy, including Protestantism, sorcery, immorality, blasphemy, Judaizing and witchcraft, as...

 in 1615, and they concluded that it could only be supported as a possibility, not as an established fact. Galileo later defended his views in Dialogue Concerning the Two Chief World Systems
Dialogue Concerning the Two Chief World Systems
The Dialogue Concerning the Two Chief World Systems was a 1632 Italian language book by Galileo Galilei comparing the Copernican system with the traditional Ptolemaic system. It was translated to Latin as Systema cosmicum in 1635 by Matthias Bernegger...

, which appeared to attack Pope Urban VIII and thus alienated him and the Jesuits, who had both supported Galileo up until this point. He was tried by the Inquisition, found "vehemently suspect of heresy", forced to recant, and spent the rest of his life under house arrest. It was while Galileo was under house arrest that he wrote one of his finest works, Two New Sciences
Two New Sciences
The Discourses and Mathematical Demonstrations Relating to Two New Sciences was Galileo's final book and a sort of scientific testament covering much of his work in physics over the preceding thirty years.After his Dialogue Concerning the Two Chief World Systems, the Roman Inquisition had banned...

. Here he summarized the work he had done some forty years earlier, on the two sciences now called kinematics
Kinematics
Kinematics is the branch of classical mechanics that describes the motion of bodies and systems without consideration of the forces that cause the motion....

 and strength of materials
Strength of materials
In materials science, the strength of a material is its ability to withstand an applied stress without failure. The applied stress may be tensile, compressive, or shear. Strength of materials is a subject which deals with loads, deformations and the forces acting on a material. A load applied to a...

.

Early life


Galileo was born in Pisa
Pisa
Pisa is a city in Tuscany, Central Italy, on the right bank of the mouth of the River Arno on the Tyrrhenian Sea. It is the capital city of the Province of Pisa...

 (then part of the Duchy of Florence
Duchy of Florence
The Duchy of Florence was an Italian monarchy that was centred on the city of Florence, in modern Tuscany, Italy. The duchy was founded in 1532 when Clement VII appointed his illegitimate son Alessandro de' Medici Duke of the Florentine Republic,...

), Italy, the first of six children of Vincenzo Galilei
Vincenzo Galilei
Vincenzo Galilei was an Italian lutenist, composer, and music theorist, and the father of the famous astronomer and physicist Galileo Galilei and of the lute virtuoso and composer Michelagnolo Galilei...

, a famous lutenist, composer, and music theorist
Music theory
Music theory is the study of how music works. It examines the language and notation of music. It seeks to identify patterns and structures in composers' techniques across or within genres, styles, or historical periods...

, and Giulia Ammannati. Four of their six children survived infancy, and the youngest Michelangelo (or Michelagnolo
Michelagnolo Galilei
Michelagnolo Galilei was an Italian composer and lutenist of the late Renaissance and early Baroque eras, active mainly in Bavaria and Poland. He was the son of music theorist and lutenist Vincenzo Galilei, and the younger brother of the renowned astronomer Galileo Galilei.- Life :Galilei was...

) also became a noted lutenist and composer.

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. He then was educated in the Camaldolese Monastery at Vallombrosa
Vallombrosa
Vallombrosa is a Benedictine abbey in the comune of Reggello , c. 30 km south-east of Florence, in the Apennines, surrounded by forests of beech and firs. It was founded by Giovanni Gualberto, a Florentine noble, in 1038 and became the mother house of the Vallumbrosan Order.It was extended...

, 35 km southeast of Florence.
Although a genuinely pious Roman Catholic, Galileo fathered three children out of wedlock with Marina Gamba
Marina Gamba
Marina Gamba of Venice was the mother of three of Galileo Galilei's illegitimate children.Marina Gamba was born around 1570 in Venice....

. 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. Their only worthy alternative was the religious life. Both girls were sent to the convent of San Matteo in Arcetri
Arcetri
Arcetri is a region of Florence, Italy, in the hills to the south of the city centre.-Landmarks:A number of historic buildings are situated there, including the house of the famous scientist Galileo Galilei ,...

 and remained there for the rest of their lives. Virginia took the name Maria Celeste
Maria Celeste
Sister Maria Celeste , born Virginia Gamba, was the daughter of the famous Italian scientist Galileo Galilei and Marina Gamba. She was the eldest of three siblings, with a sister Livia and a brother Vincenzio...

 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 legitimized
Legitimation
Legitimation or legitimization 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 in given society...

 and married Sestilia Bocchineri.

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. He did not complete this degree, but instead studied mathematics. Galileo was also studious of disegno, a term encompassing fine art, and in 1588 attained an instructor position in the Accademia delle Arti del Disegno
Accademia delle Arti del Disegno
The Accademia delle Arti del Disegno of Florence promotes the safeguard of the works of art in Italy. Founded in 1563, it was the first academy of drawing established in Europe.- History of the Accademia :...

 in Florence, teaching perspective and chiaroscuro
Chiaroscuro
Chiaroscuro in art is "an Italian term which literally means 'light-dark'. In paintings the description refers to clear tonal contrasts which are often used to suggest the volume and modelling of the subjects depicted"....

. 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
Cigoli
Lodovico Cardi , also known as Cigoli, was an Italian painter and architect of the late Mannerist and early Baroque period, trained and active in his early career in Florence, and spending the last nine years of his life in Rome.Lodovico Cardi was born at Villa Castelvecchio di Cigoli, in Tuscany,...

, who included Galileo's lunar observations in one of his paintings.

In 1589, he was appointed to the chair of mathematics in Pisa. In 1591 his father died and he was entrusted with the care of his younger brother Michelagnolo
Michelagnolo Galilei
Michelagnolo Galilei was an Italian composer and lutenist of the late Renaissance and early Baroque eras, active mainly in Bavaria and Poland. He was the son of music theorist and lutenist Vincenzo Galilei, and the younger brother of the renowned astronomer Galileo Galilei.- Life :Galilei was...

. In 1592, he moved to the University of Padua
University of Padua
The University of Padua is a premier Italian university located in the city of Padua, Italy. The University of Padua was founded in 1222 as a school of law and was one of the most prominent universities in early modern Europe. It is among the earliest universities of the world and the second...

, teaching geometry, mechanics
Mechanics
Mechanics is the branch of physics concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment....

, and astronomy until 1610. During this period Galileo made significant discoveries in both pure fundamental science
Fundamental science
Fundamental science is science that describes the most basic objects, forces, relations between them and laws governing them, such that all other phenomena may be in principle derived from them following the logic of scientific reductionism. Biology, chemistry and physics are fundamental sciences;...

 (for example, kinematics of motion and astronomy) as well as practical applied science
Applied science
Applied science is the application of scientific knowledge transferred into a physical environment. Examples include testing a theoretical model through the use of formal science or solving a practical problem through the use of natural science....

 (for example, strength of materials and improvement of the telescope). His multiple interests included the study of astrology
Astrology
Astrology consists of a number of belief systems which hold that there is a relationship between astronomical phenomena and events in the human world...

, which at the time was a discipline tied to the studies of mathematics and astronomy.

Galileo, Kepler and theories of tides



Cardinal Bellarmine had written in 1615 that the Copernican system could not be defended without "a true physical demonstration that the sun does not circle the earth but the earth circles the sun". Galileo considered his theory of the tides to provide the required physical proof of the motion of the earth. This theory was so important to Galileo that he originally intended to entitle his Dialogue on the Two Chief World Systems the Dialogue on the Ebb and Flow of the Sea. The reference to tides was removed by order of the Inquisition.

For Galileo, the tide
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....

s 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. Galileo 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
Adriatic Sea
The Adriatic Sea is a body of water separating the Italian Peninsula from the Balkan peninsula, and the system of the Apennine Mountains from that of the Dinaric Alps and adjacent ranges...

 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
Venice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...

 instead of one, about twelve hours apart. Galileo dismissed this anomaly as the result of several secondary causes, including the shape of the sea, its depth, and other factors. Against the assertion that Galileo was deceptive in making these arguments, Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...

 expressed the opinion that Galileo developed his "fascinating arguments" and accepted them uncritically out of a desire for physical proof of the motion of the Earth. Galileo dismissed as a "useless fiction" the idea, held by his contemporary Johannes Kepler
Johannes Kepler
Johannes Kepler was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican...

, that the moon caused the tides. Galileo also refused to accept Kepler's elliptical orbits of the planets, considering the circle the "perfect" shape for planetary orbits.

Controversy over comets and The Assayer


In 1619, Galileo became embroiled in a controversy with Father Orazio Grassi
Orazio Grassi
Orazio Grassi was an Italian mathematician, astronomer and architect.Canonical pertaining to Society of Jesus, he was one of the authors in controversy with Galileo Galilei on the nature of the comets....

, 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
The Assayer was a book published in Rome by Galileo Galilei in October 1623.The book was a polemic against the treatise on the comets of 1618 by Orazio Grassi, a Jesuit mathematician at the Collegio Romano. In this matter Grassi, for all his Aristotelianism, was right and Galileo was wrong...

(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. Early in 1619, Father Grassi had anonymously published a pamphlet, An Astronomical Disputation on the Three Comets of the Year 1618, which discussed the nature of a comet that had appeared late in November of the previous year. Grassi concluded that the comet was a fiery body which had moved along a segment of a great circle at a constant distance from the earth, and since it moved in the sky more slowly than the moon, it must be farther away than the moon.

Grassi's arguments and conclusions were criticized in a subsequent article, Discourse on the Comets, published under the name of one of Galileo's disciples, a Florentine lawyer named Mario Guiducci
Mario Guiducci
Mario Guiducci studied law for some time at Pisa University. Discorso Delle Comete, 1619, was published under Mario's name. However, this was mostly a work by Galileo Galilei. Galileo and Mario cooperated for some time, and this cooperation was particularly notable between 1618 and 1623, known as...

, although it had been largely written by Galileo himself. Galileo and Guiducci offered no definitive theory of their own on the nature of comets, although they did present some tentative conjectures that are now known to be mistaken. In its opening passage, Galileo and Guiducci's Discourse gratuitously insulted the Jesuit Christopher 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 regarded 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. Galileo's dispute with Grassi permanently alienated many of the Jesuits who had previously been sympathetic to his ideas, and Galileo and his friends were convinced that these Jesuits were responsible for bringing about his later condemnation. The evidence for this is at best equivocal, however.

Controversy over heliocentrism




Biblical references Psalm
Psalms
The Book of Psalms , commonly referred to simply as Psalms, is a book of the Hebrew Bible and the Christian Bible...

 , , and 1 Chronicles
Books of Chronicles
The Books of Chronicles are part of the Hebrew Bible. In the Masoretic Text, it appears as the first or last book of the Ketuvim . Chronicles largely parallels the Davidic narratives in the Books of Samuel and the Books of Kings...

  include text stating that "the world is firmly established, it cannot be moved." In the same manner, says, "the Lord set the earth on its foundations; it can never be moved." Further, Ecclesiastes
Ecclesiastes
The Book of Ecclesiastes, called , is a book of the Hebrew Bible. The English name derives from the Greek translation of the Hebrew title.The main speaker in the book, identified by the name or title Qoheleth , introduces himself as "son of David, king in Jerusalem." The work consists of personal...

  states that "And the sun rises and sets and returns to its place" etc.

Galileo defended heliocentrism
Heliocentrism
Heliocentrism, or heliocentricism, is the astronomical model in which the Earth and planets revolve around a stationary Sun at the center of the universe. The word comes from the Greek . Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center...

, and claimed it was not contrary to those Scripture passages. He took Augustine's
Augustine of Hippo
Augustine of Hippo , also known as Augustine, St. Augustine, St. Austin, St. Augoustinos, Blessed Augustine, or St. Augustine the Blessed, was Bishop of Hippo Regius . He was a Latin-speaking philosopher and theologian who lived in the Roman Africa Province...

 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.

By 1616 the attacks on the ideas of Copernicus
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....

 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, Cardinal Bellarmine, acting on directives from the Inquisition, delivered him an order not to "hold or defend" the idea that the Earth moves and the Sun stands still at the centre. The decree did not prevent Galileo from discussing heliocentrism hypothesis (thus maintaining a facade of separation between science and the church). 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
Barberini
The Barberini are a family of the Italian nobility that rose to prominence in 17th century Rome. Their influence peaked with the election of Cardinal Maffeo Barberini to the papal throne in 1623, as Pope Urban VIII...

 as Pope Urban VIII
Pope Urban VIII
Pope Urban VIII , born Maffeo Barberini, was pope from 1623 to 1644. He was the last pope to expand the papal territory by force of arms, and was a prominent patron of the arts and reformer of Church missions...

 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
Dialogue Concerning the Two Chief World Systems
The Dialogue Concerning the Two Chief World Systems was a 1632 Italian language book by Galileo Galilei comparing the Copernican system with the traditional Ptolemaic system. It was translated to Latin as Systema cosmicum in 1635 by Matthias Bernegger...

, was published in 1632, with formal authorization from the Inquisition
Inquisition
The Inquisition, Inquisitio Haereticae Pravitatis , was the "fight against heretics" by several institutions within the justice-system of the Roman Catholic Church. It started in the 12th century, with the introduction of torture in the persecution of heresy...

 and papal permission.

Dava Sobel 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 defense 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
Simplicius of Cilicia
Simplicius of Cilicia, was a disciple of Ammonius Hermiae and Damascius, and was one of the last of the Neoplatonists. He was among the pagan philosophers persecuted by Justinian in the early 6th century, and was forced for a time to seek refuge in the Persian court, before being allowed back into...

 in Latin, Simplicio in Italian), the name "Simplicio" in Italian also has the connotation of "simpleton". This portrayal of Simplicio made Dialogue Concerning the Two Chief World Systems appear as an advocacy book: an attack on Aristotelian geocentrism and defence of the Copernican theory. Unfortunately for his relationship with the Pope, Galileo put the words of Urban VIII into the mouth of Simplicio. Most historians agree Galileo did not act out of malice and felt blindsided by the reaction to his book. However, the Pope did not take the suspected public ridicule lightly, nor the Copernican advocacy. Galileo had alienated one of his biggest and most powerful supporters, the Pope, and was called to Rome to defend his writings.

With the loss of many of his defenders in Rome because of Dialogue Concerning the Two Chief World Systems, Galileo was ordered to stand trial on suspicion of heresy in 1633. The sentence of the Inquisition 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"
    Abjuration
    Abjuration is the solemn repudiation, abandonment, or renunciation by or upon oath, often the renunciation of citizenship or some other right or privilege. .-Abjuration of the realm:...

     those opinions.
  • He was sentenced to formal imprisonment at the pleasure of the Inquisition. On the following day this was commuted to house arrest, which he remained under for the rest of his life.
  • His offending Dialogue was banned; and in an action not announced at the trial, publication of any of his works was forbidden, including any he might write in the future.

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
E pur si muove!
"Eppur si muove" is an Italian phrase meaning "And yet it moves" said to have been uttered by the Italian mathematician, physicist and philosopher Galileo Galilei after being forced to recant in 1633, before the Inquisition, his belief that the Earth moves around the Sun.Some historians believe...

, 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.

After a period with the friendly Ascanio Piccolomini (the Archbishop of Siena
Siena
Siena is a city in Tuscany, Italy. It is the capital of the province of Siena.The historic centre of Siena has been declared by UNESCO a World Heritage Site. It is one of the nation's most visited tourist attractions, with over 163,000 international arrivals in 2008...

), Galileo was allowed to return to his villa at Arcetri
Arcetri
Arcetri is a region of Florence, Italy, in the hills to the south of the city centre.-Landmarks:A number of historic buildings are situated there, including the house of the famous scientist Galileo Galilei ,...

 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. It was while Galileo was under house arrest that he dedicated his time to one of his finest works, Two New Sciences
Two New Sciences
The Discourses and Mathematical Demonstrations Relating to Two New Sciences was Galileo's final book and a sort of scientific testament covering much of his work in physics over the preceding thirty years.After his Dialogue Concerning the Two Chief World Systems, the Roman Inquisition had banned...

. Here he summarized work he had done some forty years earlier, on the two sciences now called kinematics
Kinematics
Kinematics is the branch of classical mechanics that describes the motion of bodies and systems without consideration of the forces that cause the motion....

 and strength of materials
Strength of materials
In materials science, the strength of a material is its ability to withstand an applied stress without failure. The applied stress may be tensile, compressive, or shear. Strength of materials is a subject which deals with loads, deformations and the forces acting on a material. A load applied to a...

. This book has received high praise from Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...

. 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
Hernia
A hernia is the protrusion of an organ or the fascia of an organ through the wall of the cavity that normally contains it. A hiatal hernia occurs when the stomach protrudes into the mediastinum through the esophageal opening in the diaphragm....

 and insomnia
Insomnia
Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...

, so he was permitted to travel to Florence for medical advice.

Death


Galileo continued to receive visitors until 1642, when, after suffering fever and heart palpitations, he died on 8 January 1642, aged 77. The Grand Duke of Tuscany, Ferdinando II
Ferdinando II de' Medici, Grand Duke of Tuscany
Ferdinando II de' Medici was grand duke of Tuscany from 1621 to 1670. He was the eldest child of Cosimo II de' Medici and Maria Maddalena of Austria. His 49 year rule was punctuated by the terminations of the remaining operations of the Medici Bank, and the beginning of Tuscany's long economic...

, wished to bury him in the main body of the Basilica of Santa Croce
Basilica di Santa Croce di Firenze
The Basilica di Santa Croce 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 metres south east of the Duomo. The site, when first chosen, was in marshland outside the city walls...

, next to the tombs of his father and other ancestors, and to erect a marble mausoleum in his honour. These plans were scrapped, however, after Pope Urban VIII and his nephew, Cardinal Francesco Barberini, protested, because Galileo was condemned by the Catholic Church for "vehement suspicion of heresy". He was instead buried in a small room next to the novices' chapel at the end of a corridor from the southern transept of the basilica to the sacristy. He was reburied in the main body of the basilica in 1737 after a monument had been erected there in his honour; during this move, three fingers and a tooth were removed from his remains. One of these fingers, the middle finger from Galileo's right hand, is currently on exhibition at the Museo Galileo in Florence, Italy.

Scientific methods


Galileo made original contributions to the science of motion through an innovative combination of experiment and mathematics. More typical of science at the time were the qualitative studies of William Gilbert, on magnetism and electricity. Galileo's father, Vincenzo Galilei
Vincenzo Galilei
Vincenzo Galilei was an Italian lutenist, composer, and music theorist, and the father of the famous astronomer and physicist Galileo Galilei and of the lute virtuoso and composer Michelagnolo Galilei...

, a lute
Lute
Lute can refer generally to any plucked string instrument with a neck and a deep round back, or more specifically to an instrument from the family of European lutes....

nist and music theorist, had performed experiments establishing perhaps the oldest known non-linear relation in physics: for a stretched string, the pitch varies as the square root of the tension. These observations lay within the framework of the Pythagorean tradition of music, well-known to instrument makers, which included the fact that subdividing a string by a whole number produces a harmonious scale. Thus, a limited amount of mathematics had long related music and physical science, and young Galileo could see his own father's observations expand on that tradition.

Galileo was one of the first modern thinkers to clearly state that the laws of nature are mathematical. In The Assayer
The Assayer
The Assayer was a book published in Rome by Galileo Galilei in October 1623.The book was a polemic against the treatise on the comets of 1618 by Orazio Grassi, a Jesuit mathematician at the Collegio Romano. In this matter Grassi, for all his Aristotelianism, was right and Galileo was wrong...

he wrote "Philosophy is written in this grand book, the universe ... It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures;...." His mathematical analyses are a further development of a tradition employed by late scholastic natural philosophers, which Galileo learned when he studied philosophy. 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
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

 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
Inductive reasoning
Inductive reasoning, also known as induction or inductive logic, is a kind of reasoning that constructs or evaluates propositions that are abstractions of observations. It is commonly construed as a form of reasoning that makes generalizations based on individual instances...

.

Galileo showed a remarkably modern appreciation for the proper relationship between mathematics, theoretical physics, and experimental physics. He understood the parabola
Parabola
In mathematics, the parabola is a conic section, the intersection of a right circular conical surface and a plane parallel to a generating straight line of that surface...

, both in terms of conic section
Conic section
In mathematics, a conic section is a curve obtained by intersecting a cone with a plane. In analytic geometry, a conic may be defined as a plane algebraic curve of degree 2...

s and in terms of the ordinate
Ordinate
In mathematics, ordinate refers to that element of an ordered pair which is plotted on the vertical axis of a two-dimensional Cartesian coordinate system, as opposed to the abscissa...

 (y) varying as the square of the abscissa
Abscissa
In mathematics, abscissa refers to that element of an ordered pair which is plotted on the horizontal axis of a two-dimensional Cartesian coordinate system, as opposed to the ordinate...

 (x). Galilei further asserted that the parabola was the theoretically ideal trajectory
Trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...

 of a uniformly accelerated projectile in the absence of friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types 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
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 could not possibly be a parabola, but he nevertheless maintained that for distances up to the range of the artillery of his day, the deviation of a projectile's trajectory from a parabola would only be very slight.

Astronomy



Based only on uncertain descriptions of the first practical telescope, invented by Hans Lippershey
Hans Lippershey
Hans Lippershey , also known as Johann Lippershey or Lipperhey, was a German-Dutch lensmaker commonly associated with the invention of the telescope, although it is unclear if he was the first to build one.-Biography:...

 in the Netherlands in 1608, Galileo, in the following year, made a telescope with about 3x magnification. He later made improved versions with up to about 30x magnification. With a Galilean telescope the observer could see magnified, upright images on the earth—it was what is commonly known as a terrestrial telescope or a spyglass. He could also use it to observe the sky; for a time he was one of those who could construct telescopes good enough for that purpose. On 25 August 1609, he demonstrated one of his early telescopes, with a magnification of about 8 or 9, to Venetian
Venice
Venice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...

 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
Sidereus Nuncius
Sidereus Nuncius is a short treatise published in New Latin by Galileo Galilei in March 1610. It was the first scientific treatise based on observations made through a telescope...

(Starry Messenger).

Jupiter


On 7 January 1610 Galileo observed with his telescope what he described at the time as "three fixed stars, totally invisible by their smallness", all close to Jupiter, and lying on a straight line through it. Observations on subsequent nights showed that the positions of these "stars" relative to Jupiter were changing in a way that would have been inexplicable if they had really been fixed stars. On 10 January Galileo noted that one of them had disappeared, an observation which he attributed to its being hidden behind Jupiter. Within a few days he concluded that they were orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

ing Jupiter: He had discovered three of Jupiter's four largest satellites
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....

 (moons). He discovered the fourth on 13 January. These satellites are now called Io
Io (moon)
Io ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....

, Europa
Europa (moon)
Europa Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This surface is striated by cracks and...

, Ganymede
Ganymede (moon)
Ganymede is a satellite of Jupiter and the largest moon in the Solar System. It is the seventh moon and third Galilean satellite outward from Jupiter. Completing an orbit in roughly seven days, Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively...

, and Callisto
Callisto (moon)
Callisto named after the Greek mythological figure of Callisto) is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. Callisto has about 99% the diameter of the...

. Galileo named the group of four the Medicean stars, in honour of his future patron, Cosimo II de' Medici, Grand Duke of Tuscany
Cosimo II de' Medici, Grand Duke of Tuscany
Cosimo II de' Medici was Grand Duke of Tuscany from 1609 until 1621. He was the elder son of the then incumbent Grand Duke and Christina of Lorraine. He married Maria Magdalena of Austria, and had eight children....

, and Cosimo's three brothers. Later astronomers, however, renamed them Galilean satellites
Galilean moons
The Galilean moons are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance...

 in honour of their discoverer.

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
On the Heavens
On the Heavens is Aristotle's chief cosmological treatise: it contains his astronomical theory and his ideas on the concrete workings of the terrestrial world...

, 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
Christopher Clavius
Christopher Clavius was a German Jesuit mathematician and astronomer who was the main architect of the modern Gregorian calendar...

 and he received a hero's welcome when he visited Rome in 1611. Galileo continued to observe the satellites over the next eighteen months, and by mid 1611 he had obtained remarkably accurate estimates for their periods—a feat which Kepler
Johannes Kepler
Johannes Kepler was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican...

 had believed impossible.

Venus, Saturn, and Neptune


From September 1610, Galileo observed that Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

 exhibited a full set of phases
Lunar phase
A lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...

 similar to that of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

. 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
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 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, such as the Tychonic, Capellan and Extended Capellan models, each either with or without a daily rotating Earth. These all had the virtue of explaining the phases of Venus without the vice of the 'refutation' of full heliocentrism’s prediction of stellar parallax.
Galileo’s discovery of the phases of Venus was thus arguably his most empirically practically influential contribution to the two-stage transition from full geocentrism to full heliocentrism via geo-heliocentrism.

Galileo observed the planet Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.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.

Galileo also observed the planet Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...

 in 1612. It appears in his notebooks as one of many unremarkable dim stars. He did not realize that it was a planet, but he did note its motion relative to the stars before losing track of it.

Sunspots


Galileo was one of the first Europeans to observe sunspot
Sunspot
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....

s, 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
Charlemagne
Charlemagne was King of the Franks from 768 and Emperor of the Romans from 800 to his death in 814. He expanded the Frankish kingdom into an empire that incorporated much of Western and Central Europe. During his reign, he conquered Italy and was crowned by Pope Leo III on 25 December 800...

, which formerly had been attributed (impossibly) to a transit of Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

. 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. And the annual variations in sunspots' motions, discovered by Francesco Sizzi
Francesco Sizzi
Francesco Sizzi, an Italian astronomer who lived during the 17th century, is credited with being the first to notice the annual movement of sunspots.-External links:*...

 and others in 1612–1613, provided a powerful argument against both the Ptolemaic system and the geoheliocentric system of Tycho Brahe
Tycho Brahe
Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...

. 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
Christoph Scheiner
Christoph Scheiner SJ was a Jesuit priest, physicist and astronomer in Ingolstadt....

; in fact, there is little doubt that both of them were beaten by David Fabricius
David Fabricius
David Fabricius , was a German theologian who made two major discoveries in the early days of telescopic astronomy, jointly with his eldest son, Johannes Fabricius ....

 and his son Johannes
Johannes Fabricius
Johann Fabricius , eldest son of David Fabricius , was a Frisian/German astronomer and a discoverer of sunspots , independently of Galileo Galilei.-Biography:...

, 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
Thomas Harriot
Thomas Harriot was an English astronomer, mathematician, ethnographer, and translator. Some sources give his surname as Harriott or Hariot or Heriot. He is sometimes credited with the introduction of the potato to Great Britain and Ireland...

, an English mathematician and explorer, had already used what he dubbed a "perspective tube" to observe the moon. Reporting his observations, Harriot noted only "strange spottednesse" in the waning of the crescent, but was ignorant to the cause. Galileo, due in part to his artistic training and the knowledge of chiaroscuro
Chiaroscuro
Chiaroscuro in art is "an Italian term which literally means 'light-dark'. In paintings the description refers to clear tonal contrasts which are often used to suggest the volume and modelling of the subjects depicted"....

, 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 mountain
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...

s and craters
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

. 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
DANTE
Delivery of Advanced Network Technology to Europe is a not-for-profit organisation that plans, builds and operates the international networks that interconnect the various national research and education networks in Europe and surrounding regions...

.

Milky Way and Stars


Galileo observed the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

, previously believed to be nebulous
Nebula
A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases...

, and found it to be a multitude of star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

s 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
Mizar (star)
The Mizar–Alcor stellar sextuple system consists of the quadruple system Mizar and the binary system Alcor.- Description :Mizar is a quadruple system of two binary stars in the constellation Ursa Major and is the second star from the end of the Big Dipper's handle. Its apparent magnitude is 2.23...

 in Ursa Major in 1617.

In the Starry Messenger Galileo reported that stars appeared as mere blazes of light, essentially unaltered in appearance by the telescope, and contrasted them to planets, which the telescope revealed to be discs. But shortly thereafter, in his letters on sunspots, he reported that the telescope revealed the shapes of both stars and planets to be "quite round". From that point forward he continued to report that telescopes showed the roundness of stars, and that stars seen through the telescope measured a few seconds of arc in diameter. He also devised a method for measuring the apparent size of a star without a telescope. As described in his Dialogue Concerning the two Chief World Systems, his method was to hang a thin rope in his line of sight to the star and measure the maximum distance from which it would wholly obscure the star. From his measurements of this distance and of the width of the rope he could calculate the angle subtended by the star at his viewing point. In his Dialogue he reported that he had found the apparent diameter of a star of first magnitude to be no more than 5 arcseconds, and that of one of sixth magnitude to be about 5/6 arcseconds. Like most astronomers of his day, Galileo did not recognize 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
Magnitude (astronomy)
Magnitude is the logarithmic measure of the brightness of an object, in astronomy, measured in a specific wavelength or passband, usually in optical or near-infrared wavelengths.-Background:...

) 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
Simon Marius
Simon Marius was a German astronomer. He was born in Gunzenhausen, near Nuremberg, but he spent most of his life in the city of Ansbach....

, Giovanni Battista Riccioli
Giovanni Battista Riccioli
Giovanni Battista Riccioli was an Italian astronomer and a Catholic priest in the Jesuit order...

, and Martinus Hortensius
Martin van den Hove
Martin van den Hove was a Dutch astronomer and mathematician. His adopted Latin name is a translation of the Dutch hof , in Latin horta.-Early life:...

 made similar measurements of stars, and Marius and Riccioli concluded the smaller sizes were not small enough to answer Tycho's argument.

Technology


Galileo made a number of contributions to what is now known as technology
Technology
Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...

, 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
Artillery
Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...

 and surveyors
Surveying
See Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...

. This expanded on earlier instruments designed by Niccolò Tartaglia and Guidobaldo del Monte
Guidobaldo del Monte
Guidobaldo del Monte , Marquis del Monte, was an Italian mathematician, philosopher and astronomer of the 16th century.- Biography :...

. For gunners, it offered, in addition to a new and safer way of elevating cannon
Cannon
A cannon is any piece of artillery that uses gunpowder or other usually explosive-based propellents to launch a projectile. Cannon vary in caliber, range, mobility, rate of fire, angle of fire, and firepower; different forms of cannon combine and balance these attributes in varying degrees,...

s accurately, a way of quickly computing the charge of gunpowder
Gunpowder
Gunpowder, also known since in the late 19th century as black powder, was the first chemical explosive and the only one known until the mid 1800s. It is a mixture of sulfur, charcoal, and potassium nitrate - with the sulfur and charcoal acting as fuels, while the saltpeter works as an oxidizer...

 for cannonballs
Round shot
Round shot is a solid projectile without explosive charge, fired from a cannon. As the name implies, round shot is spherical; its diameter is slightly less than the bore of the gun it is fired from.Round shot was made in early times from dressed stone, but by the 17th century, from iron...

 of different sizes and materials. As a geometric instrument, it enabled the construction of any regular polygon
Polygon
In geometry a polygon is a flat shape consisting of straight lines that are joined to form a closed chain orcircuit.A polygon is traditionally a plane figure that is bounded by a closed path, composed of a finite sequence of straight line segments...

, 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
Marc'Antonio Mazzoleni
Marc'Antonio Mazzoleni was a Paduan instrument maker best known for his association with Galileo Galilei, for whom Mazzoleni produced instruments including Galileo's military compasses and other instruments....

 produced more than 100 of these compasses, which Galileo sold (along with an instruction manual he wrote) for 50 lire and offered a course of instruction in the use of the compasses for 120 lire.

In about 1593
Timeline of temperature and pressure measurement technology
Timeline of temperature and pressure measurement technology A history of temperature measurement and pressure measurement technology.-1500s:* 1592-1593 — Galileo Galilei builds a device showing variation of hotness known as the thermoscope using the contraction of air to draw water up a...

, Galileo constructed a thermometer
Galileo thermometer
A Galileo thermometer , named after Italian physicist Galileo Galilei, is a thermometer made of a sealed glass cylinder containing a clear liquid and a series of objects whose densities are such that they rise or fall as the temperature changes...

, using the expansion and contraction of air in a bulb to move water in an attached tube.

In 1609, Galileo was, along with Englishman Thomas Harriot
Thomas Harriot
Thomas Harriot was an English astronomer, mathematician, ethnographer, and translator. Some sources give his surname as Harriott or Hariot or Heriot. He is sometimes credited with the introduction of the potato to Great Britain and Ireland...

 and others, among the first to use a refracting telescope
Refracting telescope
A refracting or refractor telescope is a type of optical telescope that uses a lens as its objective to form an image . The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used for long focus camera lenses...

 as an instrument to observe stars, planets or moons. The name "telescope" was coined for Galileo's instrument by a Greek mathematician, Giovanni Demisiani
Giovanni Demisiani
Giovanni Demisiani , a Greek from Zakynthos, was a theologian, chemist, mathematician to Cardinal Gonzaga, and member of the Accademia dei Lincei...

, at a banquet held in 1611 by Prince Federico Cesi
Federico Cesi
Federico Angelo Cesi was an Italian scientist, naturalist, and founder of the Accademia dei Lincei. On his father's death in 1630, he became briefly lord of Acquasparta.- Biography :...

 to make Galileo a member of his Accademia dei Lincei
Accademia dei Lincei
The Accademia dei Lincei, , is an Italian science academy, located at the Palazzo Corsini on the Via della Lungara in Rome, Italy....

. The name was derived from the Greek tele = 'far' and skopein = 'to look or see'. In 1610, he used a telescope at close range to magnify the parts of insects. By 1624 Galileo had perfected a compound microscope
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...

. He gave one of these instruments to Cardinal Zollern in May of that year for presentation to the Duke of Bavaria, and in September he sent another to Prince Cesi. The Linceans
Accademia dei Lincei
The Accademia dei Lincei, , is an Italian science academy, located at the Palazzo Corsini on the Via della Lungara in Rome, Italy....

 played a role again in naming the "microscope" a year later when fellow academy member Giovanni Faber
Giovanni Faber
Giovanni Faber was a German papal doctor, botanist and art collector, originally from Bamberg in Bavaria, who lived in Rome from 1598. He was curator of the Vatican botanical garden, a member and the secretary of the Accademia dei Lincei. He acted throughout his career as a political broker...

 coined the word for Galileo's invention from the Greek words μικρόν (micron) meaning "small", and σκοπεῖν (skopein) meaning "to look at". The word was meant to be analogous with "telescope". Illustrations of insects made using one of Galileo's microscopes, and published in 1625, appear to have been the first
Timeline of microscope technology
Timeline of microscope technology* 1590 - Dutch spectacle-makers Hans Jansen and his son Zacharias Jansen, claimed by later writers to have invented a compound microscope....

 clear documentation of the use of a compound microscope.

In 1612, having determined the orbital periods of Jupiter's satellites, Galileo proposed that with sufficiently accurate knowledge of their orbits one could use their positions as a universal clock, and this would make possible the determination of longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

. He worked on this problem from time to time during the remainder of his life; but the practical problems were severe. The method was first successfully applied by Giovanni Domenico Cassini
Giovanni Domenico Cassini
This article is about the Italian-born astronomer. For his French-born great-grandson, see Jean-Dominique Cassini.Giovanni Domenico Cassini was an Italian/French mathematician, astronomer, engineer, and astrologer...

 in 1681 and was later used extensively for large land surveys; this method, for example, was used by Lewis and Clark. For sea navigation, where delicate telescopic observations were more difficult, the longitude problem eventually required development of a practical portable marine chronometer
Marine chronometer
A marine chronometer is a clock that is precise and accurate enough to be used as a portable time standard; it can therefore be used to determine longitude by means of celestial navigation...

, such as that of John Harrison
John Harrison
John Harrison was a self-educated English clockmaker. He invented the marine chronometer, a long-sought device in solving the problem of establishing the East-West position or longitude of a ship at sea, thus revolutionising and extending the possibility of safe long distance sea travel in the Age...

.
In his last year, when totally blind, he designed an escapement
Escapement
In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...

 mechanism for a pendulum clock (called Galileo's escapement
Galileo's escapement
Galileo's escapement is a design for a clock escapement, invented by Galileo Galilei.While observing, and timing with his pulse, the swinging of lamps in the cathedral at Pisa, Galileo realized that their apparent isochronicity could be used for timekeeping...

), a vectorial model of which may be seen here
Galileo's escapement
Galileo's escapement is a design for a clock escapement, invented by Galileo Galilei.While observing, and timing with his pulse, the swinging of lamps in the cathedral at Pisa, Galileo realized that their apparent isochronicity could be used for timekeeping...

. The first fully operational pendulum clock was made by Christiaan Huygens in the 1650s.

Physics



Galileo's theoretical and experimental work on the motions of bodies, along with the largely independent work of Kepler and René Descartes
René Descartes
René Descartes ; was a French philosopher and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day...

, was a precursor of the classical mechanics
Classical mechanics
In physics, classical mechanics is one of the two major sub-fields of mechanics, which is concerned with the set of physical laws describing the motion of bodies under the action of a system of forces...

 developed by Sir Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...

. Galileo conducted several experiments with pendulum
Pendulum
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...

s. It is popularly believed (thanks to the biography by Vincenzo Viviani
Vincenzo Viviani
Vincenzo Viviani was an Italian mathematician and scientist. He was a pupil of Torricelli and a disciple of Galileo.-Biography:...

) 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
Two New Sciences
The Discourses and Mathematical Demonstrations Relating to Two New Sciences was Galileo's final book and a sort of scientific testament covering much of his work in physics over the preceding thirty years.After his Dialogue Concerning the Two Chief World Systems, the Roman Inquisition had banned...

. Galileo claimed that a simple pendulum is isochronous, i.e. that its swings always take the same amount of time, independently of the amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...

. In fact, this is only approximately true, 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
Verge escapement
The verge escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by advancing the gear train at regular intervals or 'ticks'. Its origin is unknown. Verge escapements were used from the 14th century until about 1800 in clocks...

, 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. Sometime between Galileo's death and 1667, the members of the Florentine Accademia del Cimento
Accademia del Cimento
The Accademia del Cimento , an early scientific society, was founded in Florence 1657 by students of Galileo, Giovanni Alfonso Borelli and Vincenzo Viviani. The foundation of Academy was funded by Prince Leopoldo and Grand Duke Ferdinando II de' Medici...

repeated the experiment over a distance of about a mile and obtained a similarly inconclusive result. Galileo put forward the basic principle of relativity
Galilean invariance
Galilean invariance or Galilean relativity is a principle of relativity which states that the fundamental laws of physics are the same in all inertial frames...

, 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
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...

 special theory of relativity.

Falling Bodies


A biography by Galileo's pupil Vincenzo Viviani
Vincenzo Viviani
Vincenzo Viviani was an Italian mathematician and scientist. He was a pupil of Torricelli and a disciple of Galileo.-Biography:...

 stated that Galileo had dropped balls
Galileo's Leaning Tower of Pisa experiment
right|thumb|Hammer and Feather Drop - [[Apollo 15]] [[astronaut]] [[David Scott]] on the Moon recreating Galileo's famous experiment....

 of the same material, but different mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

es, from the Leaning Tower of Pisa
Leaning Tower of Pisa
The Leaning Tower of Pisa or simply the Tower of Pisa is the campanile, or freestanding bell tower, of the cathedral of the Italian city of Pisa...

 to demonstrate that their time of descent was independent of their mass. This was contrary to what Aristotle had taught: that heavy objects fall faster than lighter ones, in direct proportion to weight. While this story has been retold in popular accounts, there is no account by Galileo himself of such an experiment, and it is generally accepted by historians that it was at most a thought experiment
Thought experiment
A thought experiment or Gedankenexperiment considers some hypothesis, theory, or principle for the purpose of thinking through its consequences...

 which did not actually take place.

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
Lucretius
Titus Lucretius Carus was a Roman poet and philosopher. His only known work is an epic philosophical poem laying out the beliefs of Epicureanism, De rerum natura, translated into English as On the Nature of Things or "On the Nature of the Universe".Virtually no details have come down concerning...

 and Simon Stevin
Simon Stevin
Simon Stevin was a Flemish mathematician and military engineer. He was active in a great many areas of science and engineering, both theoretical and practical...

. Cristiano Banti's Salviati also held it could be experimentally demonstrated by the comparison of pendulum motions in air with bobs of lead and of cork which had different weight but which were otherwise similar.

Galileo proposed that a falling body would fall with a uniform acceleration, as long as the resistance of the medium through which it was falling remained negligible, or in the limiting case of its falling through a vacuum. He also derived the correct kinematical law for the distance travelled during a uniform acceleration starting from rest—namely, that it is proportional to the square of the elapsed time ( d ∝ t 2 ). 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, and Domingo de Soto
Domingo de Soto
Domingo de Soto was a Dominican priest and Scholastic theologian born in Segovia, Spain, and died in Salamanca at the age of 66...

, in the 16th, had suggested that bodies falling through a homogeneous medium would be uniformly accelerated. Galileo expressed the time-squared law using geometrical constructions and mathematically precise words, adhering to the standards of the day. (It remained for others to re-express the law in algebraic terms). He also concluded that objects retain their velocity unless a force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

—often friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of 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
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...

 had been proposed by John Philoponus
John Philoponus
John Philoponus , also known as John the Grammarian or John of Alexandria, was a Christian and Aristotelian commentator and the author of a considerable number of philosophical treatises and theological works...

 centuries earlier, as had Jean Buridan
Jean Buridan
Jean Buridan was a French priest who sowed the seeds of the Copernican revolution in Europe. Although he was one of the most famous and influential philosophers of the late Middle Ages, he is today among the least well known...

, and according to Joseph Needham
Joseph Needham
Noel Joseph Terence Montgomery Needham, CH, FRS, FBA , also known as Li Yuese , was a British scientist, historian and sinologist known for his scientific research and writing on the history of Chinese science. He was elected a fellow of the Royal Society in 1941, and as a fellow of the British...

, 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
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

, 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
Newton's laws of motion
Newton's laws of motion are three physical laws that form the basis for classical mechanics. They describe the relationship between the forces acting on a body and its motion due to those forces...

 (first law).

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
Euclid's Elements
Euclid's Elements is a mathematical and geometric treatise consisting of 13 books written by the Greek mathematician Euclid in Alexandria c. 300 BC. It is a collection of definitions, postulates , propositions , and mathematical proofs of the propositions...

. 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
René Descartes
René Descartes ; was a French philosopher and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day...

.

Galileo produced one piece of original and even prophetic work in mathematics: Galileo's paradox
Galileo's paradox
Galileo's paradox is a demonstration of one of the surprising properties of infinite sets.In his final scientific work, the Two New Sciences, Galileo Galilei made two apparently contradictory statements about the positive whole numbers...

, which shows that there are as many perfect squares as there are whole numbers, even though most numbers are not perfect squares.

His writings


Galileo's early works describing scientific instruments include the 1586 tract entitled The Little Balance (La Billancetta) describing an accurate balance to weigh objects in air or water and the 1606 printed manual Le Operazioni del Compasso Geometrico et Militare on the operation of a geometrical and military compass.

His early works in dynamics, the science of motion and mechanics were his 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
Sidereus Nuncius is a short treatise published in New Latin by Galileo Galilei in March 1610. It was the first scientific treatise based on observations made through a telescope...

(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
    Galilean moons
    The Galilean moons are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance...

    ;
  • 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
    Milky Way
    The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

    ; 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 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. In 1616, after the order by the inquisition for Galileo not to hold or defend the Copernican position, Galileo wrote the Discourse on the tides (Discorso sul flusso e il reflusso del mare) based on the Copernican earth, in the form of a private letter to Cardinal Orsini. In 1619, Mario Guiducci, a pupil of Galileo's, published a lecture written largely by Galileo under the title Discourse on the Comets (Discorso Delle Comete), arguing against the Jesuit interpretation of comets.

In 1623, Galileo published The Assayer
The Assayer
The Assayer was a book published in Rome by Galileo Galilei in October 1623.The book was a polemic against the treatise on the comets of 1618 by Orazio Grassi, a Jesuit mathematician at the Collegio Romano. In this matter Grassi, for all his Aristotelianism, was right and Galileo was wrong...

—Il Saggiatore
, which attacked theories based on Aristotle's authority and promoted experimentation and the mathematical formulation of scientific ideas. The book was highly successful and even found support among the higher echelons of the Christian church. Following the success of The Assayer, Galileo published the Dialogue Concerning the Two Chief World Systems (Dialogo sopra i due massimi sistemi del mondo) in 1632. Despite taking care to adhere to the Inquisition's 1616 instructions, the claims in the book favouring Copernican theory and a non Geocentric model of the solar system led to Galileo being tried and banned on publication. Despite the publication ban, Galileo published his Discourses and Mathematical Demonstrations Relating to Two New Sciences
Two New Sciences
The Discourses and Mathematical Demonstrations Relating to Two New Sciences was Galileo's final book and a sort of scientific testament covering much of his work in physics over the preceding thirty years.After his Dialogue Concerning the Two Chief World Systems, the Roman Inquisition had banned...

(Discorsi e Dimostrazioni Matematiche, intorno a due nuove scienze) in 1638 in Holland
House of Elzevir
Elzevir is the name of a celebrated family of Dutch booksellers, publishers, and printers of the 17th and early 18th centuries. The duodecimo series of "Elzevirs" became very famous and very desirable among bibliophiles, who sought to obtain the tallest and freshest copies of these tiny...

, outside the jurisdiction of the Inquisition.
  • The Little Balance (1586)
  • On Motion (1590)
  • Mechanics (ca. 1600)
  • The Starry Messenger
    Sidereus Nuncius
    Sidereus Nuncius is a short treatise published in New Latin by Galileo Galilei in March 1610. It was the first scientific treatise based on observations made through a telescope...

    (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
    The Assayer
    The Assayer was a book published in Rome by Galileo Galilei in October 1623.The book was a polemic against the treatise on the comets of 1618 by Orazio Grassi, a Jesuit mathematician at the Collegio Romano. In this matter Grassi, for all his Aristotelianism, was right and Galileo was wrong...

    (1623; in Italian, Il Saggiatore)
  • Dialogue Concerning the Two Chief World Systems
    Dialogue Concerning the Two Chief World Systems
    The Dialogue Concerning the Two Chief World Systems was a 1632 Italian language book by Galileo Galilei comparing the Copernican system with the traditional Ptolemaic system. It was translated to Latin as Systema cosmicum in 1635 by Matthias Bernegger...

    (1632; in Italian Dialogo dei due massimi sistemi del mondo)
  • Discourses and Mathematical Demonstrations Relating to Two New Sciences
    Two New Sciences
    The Discourses and Mathematical Demonstrations Relating to Two New Sciences was Galileo's final book and a sort of scientific testament covering much of his work in physics over the preceding thirty years.After his Dialogue Concerning the Two Chief World Systems, the Roman Inquisition had banned...

    (1638; in Italian, Discorsi e Dimostrazioni Matematiche, intorno a due nuove scienze)

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. In 1741 Pope Benedict XIV
Pope Benedict XIV
Pope Benedict XIV , born Prospero Lorenzo Lambertini, was Pope from 17 August 1740 to 3 May 1758.-Life:...

 authorized the publication of an edition of Galileo's complete scientific works which included a mildly censored version of the Dialogue. In 1758 the general prohibition against works advocating heliocentrism was removed from the Index of prohibited books
Index Librorum Prohibitorum
The Index Librorum Prohibitorum was a list of publications prohibited by the Catholic Church. A first version was promulgated by Pope Paul IV in 1559, and a revised and somewhat relaxed form was authorized at the Council of Trent...

, although the specific ban on uncensored versions of the Dialogue and Copernicus's De Revolutionibus remained. All traces of official opposition to heliocentrism by the church disappeared in 1835 when these works were finally dropped from the Index.

In 1939 Pope Pius XII
Pope Pius XII
The Venerable Pope Pius XII , born Eugenio Maria Giuseppe Giovanni Pacelli , reigned as Pope, head of the Catholic Church and sovereign of Vatican City State, from 2 March 1939 until his death in 1958....

, in his first speech to the Pontifical Academy of Sciences, within a few months of his election to the papacy, described Galileo as being among the "most audacious heroes of research... not afraid of the stumbling blocks and the risks on the way, nor fearful of the funereal monuments". His close advisor of 40 years, Professor Robert Leiber wrote: "Pius XII was very careful not to close any doors (to science) prematurely. He was energetic on this point and regretted that in the case of Galileo."

On 15 February 1990, in a speech delivered at the Sapienza University of Rome, Cardinal Ratzinger (later to become Pope Benedict XVI
Pope Benedict XVI
Benedict XVI is the 265th and current Pope, by virtue of his office of Bishop of Rome, the Sovereign of the Vatican City State and the leader of the Catholic Church as well as the other 22 sui iuris Eastern Catholic Churches in full communion with the Holy See...

) cited some current views on the Galileo affair as forming what he called "a symptomatic case that permits us to see how deep the self-doubt of the modern age, of science and technology goes today". Some of the views he cited were those of the philosopher Paul Feyerabend
Paul Feyerabend
Paul Karl Feyerabend was an Austrian-born philosopher of science best known for his work as a professor of philosophy at the University of California, Berkeley, where he worked for three decades . He lived a peripatetic life, living at various times in England, the United States, New Zealand,...

, whom he quoted as saying "The Church at the time of Galileo kept much more closely to reason than did Galileo himself, and she took into consideration the ethical and social consequences of Galileo's teaching too. Her verdict against Galileo was rational and just and the revision of this verdict can be justified only on the grounds of what is politically opportune." The Cardinal did not clearly indicate whether he agreed or disagreed with Feyerabend's assertions. He did, however, say "It would be foolish to construct an impulsive apologetic on the basis of such views."

On 31 October 1992, Pope John Paul II
Pope John Paul II
Blessed Pope John Paul II , born Karol Józef Wojtyła , reigned as Pope of the Catholic Church and Sovereign of Vatican City from 16 October 1978 until his death on 2 April 2005, at of age. His was the second-longest documented pontificate, which lasted ; only Pope Pius IX ...

 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
Pontifical Council for Culture
The Pontifical Council for Culture is a department of the Roman Curia charged with fostering the relationship of the Catholic Church with different cultures. Pope John Paul II founded it on 20 May 1982...

. In March 2008 the head of the Pontifical Academy of Sciences, Nicola Cabibbo, announced a plan to honour Galileo by erecting a statue of him inside the Vatican walls. In December of the same year, during events to mark the 400th anniversary of Galileo's earliest telescopic observations, Pope Benedict XVI praised his contributions to astronomy. A month later, however, the head of the Pontifical Council for Culture, Gianfranco Ravasi, revealed that the plan to erect a statue of Galileo in the grounds of the Vatican had been suspended.

Impact on modern science


According to Stephen Hawking
Stephen Hawking
Stephen William Hawking, CH, CBE, FRS, FRSA is an English theoretical physicist and cosmologist, whose scientific books and public appearances have made him an academic celebrity...

, Galileo probably bears more of the responsibility for the birth of modern science than anybody else, and Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...

 called him the father of modern science.

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
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

 discovered by Galileo (Io
Io (moon)
Io ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....

, Europa
Europa (moon)
Europa Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This surface is striated by cracks and...

, Ganymede
Ganymede (moon)
Ganymede is a satellite of Jupiter and the largest moon in the Solar System. It is the seventh moon and third Galilean satellite outward from Jupiter. Completing an orbit in roughly seven days, Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively...

 and Callisto
Callisto (moon)
Callisto named after the Greek mythological figure of Callisto) is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. Callisto has about 99% the diameter of the...

) as the Galilean moons
Galilean moons
The Galilean moons are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance...

. Other scientific endeavours and principles are named after Galileo including the Galileo spacecraft, the first spacecraft to enter orbit around Jupiter, the proposed Galileo global satellite navigation system
Global Navigation Satellite System
A satellite navigation or SAT NAV system is a system of satellites that provide autonomous geo-spatial positioning with global coverage. It allows small electronic receivers to determine their location to within a few metres using time signals transmitted along a line-of-sight by radio from...

, the transformation between inertial systems in classical mechanics
Classical mechanics
In physics, classical mechanics is one of the two major sub-fields of mechanics, which is concerned with the set of physical laws describing the motion of bodies under the action of a system of forces...

 denoted Galilean transformation
Galilean transformation
The Galilean transformation is used to transform between the coordinates of two reference frames which differ only by constant relative motion within the constructs of Newtonian physics. This is the passive transformation point of view...

 and the Gal (unit)
Gal (unit)
The gal, sometimes called galileo, is a unit of acceleration used extensively in the science of gravimetry. The gal is defined as 1 centimeter per second squared ....

, sometimes known as the Galileo which is a non-SI
Si
Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...

 unit of acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

.


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
International Year of Astronomy
The International Year of Astronomy was a year-long celebration of astronomy that took place in 2009 to coincide with the 400th anniversary of the first recorded astronomical observations with a telescope by Galileo Galilei and the publication of Johannes Kepler's Astronomia nova in the 17th century...

. A global scheme was laid out by the International Astronomical Union
International Astronomical Union
The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...

 (IAU), also endorsed by UNESCO
UNESCO
The United Nations Educational, Scientific and Cultural Organization is a specialized agency of the United Nations...

—the UN body responsible for Educational, Scientific and Cultural matters. The International Year of Astronomy
International Year of Astronomy
The International Year of Astronomy was a year-long celebration of astronomy that took place in 2009 to coincide with the 400th anniversary of the first recorded astronomical observations with a telescope by Galileo Galilei and the publication of Johannes Kepler's Astronomia nova in the 17th century...

 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
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

 697 Galilea
697 Galilea
697 Galilea is a minor planet orbiting the Sun. It was named in honour of Galileo Galilei, as it was discovered just after the 300th anniversary of his discovery of the Galilean moons.-External links:*...

 is named in his honour.

In artistic and popular media


Galileo is mentioned several times in the "opera" section of the Queen
Queen (band)
Queen are a British rock band formed in London in 1971, originally consisting of Freddie Mercury , Brian May , John Deacon , and Roger Taylor...

 song, "Bohemian Rhapsody
Bohemian Rhapsody
"Bohemian Rhapsody" is a song by the British rock band Queen. It was written by Freddie Mercury for the band's 1975 album A Night at the Opera...

". He features prominently in the song "Galileo
Galileo (Indigo Girls song)
"Galileo" is a song written by Emily Saliers and recorded and performed by folk rock group the Indigo Girls. It was released in 1992 on their platinum-selling fourth studio album Rites of Passage. It reached #10 on the Billboard Modern Rock Tracks chart, the first song by the Indigo Girls to break...

" performed by the Indigo Girls
Indigo Girls
The Indigo Girls are an American folk rock music duo, consisting of Amy Ray and Emily Saliers. They met in elementary school and began performing together as high school students in Decatur, Georgia, part of the Atlanta metropolitan area...

.

Twentieth-century plays have been written on Galileo's life, including Life of Galileo
Life of Galileo
Life of Galileo , also known as Galileo, is a play by the twentieth-century German dramatist Bertolt Brecht. The first version of the play was written between 1937 and 1939; the second version was written between 1945–1947, in collaboration with Charles Laughton...

(1943) by the German playwright Bertolt Brecht
Bertolt Brecht
Bertolt Brecht was a German poet, playwright, and theatre director.An influential theatre practitioner of the 20th century, Brecht made equally significant contributions to dramaturgy and theatrical production, the latter particularly through the seismic impact of the tours undertaken by the...

, with a film adaptation
Galileo (film)
Galileo is a 1975 film version of the Bertolt Brecht play The Life of Galileo. The film was produced and released as part of the American Film Theatre, which adapted theatrical works for a subscription-driven cinema series.-Plot:...

 (1975) of it, and Lamp At Midnight
Lamp At Midnight
Lamp At Midnight is a play by Barrie Stavis, first produced at New Stages, New York, in 1947. A television adaptation appeared in the Hallmark Hall of Fame series in 1966...

(1947) by Barrie Stavis
Barrie Stavis
Barrie Stavis was a distinguished American playwright. He has authored several powerful plays about men struggling in the vortex of history. They advocate ideas, suffer, often are executed, but eventually their ideas win. The heresy of one age becomes the established truth of the next...

, as well as the 2008 play "Galileo Galilei".

Kim Stanley Robinson
Kim Stanley Robinson
Kim Stanley Robinson is an American science fiction writer known for his award-winning Mars trilogy. His work delves into ecological and sociological themes regularly, and many of his novels appear to be the direct result of his own scientific fascinations, such as the fifteen years of research...

 wrote a science fiction novel entitled Galileo's Dream
Galileo's Dream
Galileo's Dream is a science fiction novel with elements of historical fiction written by author Kim Stanley Robinson. It describes the life of 17th century scientist and astronomer Galileo Galilei, and the far-future society living on the Galilean moons he discovered.It was published in hardcover...

(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.

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
Isaac Newton Telescope
The Isaac Newton Telescope or INT is a 2.54 m optical telescope run by the ING at Roque de los Muchachos Observatory on La Palma in the Canary Islands since 1984....

, the observatory in Kremsmünster Abbey
Kremsmünster Abbey
Kremsmünster Abbey is a Benedictine monastery in Kremsmünster in Upper Austria.-History:The monastery was founded in 777 by Tassilo III, Duke of Bavaria...

, a modern telescope, a radio telescope
Radio telescope
A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes...

 and a space telescope
Space observatory
A space observatory is any instrument in outer space which is used for observation of distant planets, galaxies, and other outer space objects...

. In 2009, the Galileoscope
Galileoscope
The Galileoscope is a small , mass-produced refractor telescope, designed with the intention of increasing public interest in astronomy and science...

 was also released. This is a mass-produced, low-cost educational 2 inches (50.8 mm) telescope with relatively high quality.

See also

  • Catholic Church and science
  • Villa Il Gioiello
    Villa Il Gioiello
    Villa il Gioiello is a villa in Florence, central Italy, famous for being one of the residences of Galileo Galilei, which he lived in from 1631 until his death in 1642...

     (Galileo's main home in Florence)

By Galileo


On Galileo


Biography


Galileo and the Church