Galileo Confirms the Heliocentric Model of the Solar System

Galileo, through his observations and analyses, confirmed Copernicus’s heliocentric model of the solar system, which led to an inevitable clash between scientific inquiry and the traditional geocentric beliefs of Aristotelian philosophy.

Summary of Event

Galileo’s Sidereus nuncius (1610; The Sidereal Messenger
Sidereal Messenger, The (Galileo) , 1880; also known as The Starry Messenger) created a sensation throughout Europe, with poets comparing his scientific discoveries to the feats of explorer Christopher Columbus during the Renaissance. In the book, Galileo reported observing the heavens through a spyglass, later called a refracting telescope Telescope;Galileo and . After improving the magnification of the original Dutch spyglass, Galileo made additional observations during 1609-1610 and, for the first time, diagramed the distant stars of the Milky Way, the constellation Cancer, and the nebula Praesepe. He also proclaimed that Earth’s moon was not as smooth as previously believed by Aristotle and his supporters. Instead, the Moon was pitted with mountains, valleys, and craters. Within a two-month period, Galileo watched and sketched the horned moon change its shape. [kw]Galileo Confirms the Heliocentric Model of the Solar System (1610)
[kw]Solar System, Galileo Confirms the Heliocentric Model of the (1610)
[kw]Heliocentric Model of the Solar System, Galileo Confirms the (1610)
Astronomy;1610: Galileo Confirms the Heliocentric Model of the Solar System[0550]
Physics;1610: Galileo Confirms the Heliocentric Model of the Solar System[0550]
Science and technology;1610: Galileo Confirms the Heliocentric Model of the Solar System[0550]
Cultural and intellectual history;1610: Galileo Confirms the Heliocentric Model of the Solar System[0550]
Italy;1610: Galileo Confirms the Heliocentric Model of the Solar System[0550]
Solar system, heliocentric model
Astronomy;heliocentric model of the solar system
Copernicus, Nicolaus
Medici, Cosimo II de’
Paul V
Urban VIII

Turning his telescope on distant Jupiter, he observed strange lights nearby that changed positions over several weeks and deduced that they orbited Jupiter as the Moon orbits Earth. These objects were, in fact, the moons of Jupiter. Galileo named them the “Medicean stars” to honor his patrons, the Medici rulers of Florence. Galileo also observed lights around Saturn, later identified as the rings of Saturn.

Galileo’s book also advanced his own career, for he was appointed mathematician-philosopher to Cosimo II de’ Medici, Medici, Cosimo II de’[Medici, Cosmio 02 de] the grand duke of Tuscany, who became a strong patron and protector of Galileo during the next ten years. More important, The Sidereal Messenger became a milestone in Galileo’s march toward total acceptance of the heliocentric theory of the solar system as espoused by Nicolaus Copernicus Copernicus, Nicolaus . At first, Galileo had not questioned the traditional beliefs of Aristotelian philosophy that state that Earth stood stationary at the center of the universe, with the stars and Sun revolving around it. By 1597, however, he found Copernicus’s ideas of planetary motion around the Sun more plausible. Galileo’s telescopic observations of the changing moon, of Jupiter and Saturn, and of other stars during 1609-1610 provided ample evidence that Aristotle’s claims were false.

Galileo’s conviction that the heliocentric model was correct deepened in late 1610, when he observed through his telescope the sunlight on Venus, which glided across that planet in similar fashion to that of Earth’s moon. He noted the phases of sunlight on Venus, changing from a sliver to a full circle. To Galileo, Aristotle’s beliefs could not account for these changes, but Copernicus’s heliocentric theory could.

Galileo became so enamored with heliocentricity and his telescopic discoveries that he cast caution aside in promoting the unorthodox heliocentric theory. In doing so, he inadvertently challenged the Roman Catholic Church, which held firmly to Aristotle’s beliefs because Aristotelian concepts supported biblical accounts of the universe. In 1611, for example, Galileo displayed his telescope to Pope Paul V Paul V[Paul 05] , who made strong objections to Galileo’s scientific observation of the heavens. In a series of letters made public by Galileo’s enemies in 1613-1614, Galileo offended Church leaders by arguing that the heliocentric theory was compatible with Catholic doctrine and proper interpretation of the Bible. When Galileo’s letters on sunspots (1613) appeared, he contradicted the Church’s views that the heavens were perfect and unchanging, since his telescope revealed black blemishes randomly scudding across the Sun’s surface. Galileo arrogantly dismissed the swelling ranks of angry priests and professors who resented and envied him, belittling them as ignorant and inadequate. In turn, these individuals accused Galileo of spreading evil doctrine, crossing over into theology, contradicting Scripture, and even challenging the authority of the Catholic Church. Catholicism;science and

A statue of Galileo.

(George L. Shuman)

Between 1613 and 1631, the Catholic Church warned Galileo to abandon the heliocentric model of the heavens. The Church felt threatened by Reform movements sweeping Protestant Germany, the Netherlands, England, and Scandinavia, along with the unrest seething in France. The Catholic Church checked further threats to its power and influence by means of the Inquisition Inquisition , a tribunal established to discover, suppress, and punish heresy and teachings contrary to Church doctrine. The Church feared unauthorized ideas, so it banned speeches, burned books, and even resorted to burning blasphemers at the stake.

In 1616, Pope Paul V officially denounced the heliocentric theory and placed the works of Nicolaus Copernicus on the Index of Forbidden Books, reasoning that Copernican ideas endangered Church tenets. The pope also summoned Galileo to Rome to determine the orthodoxy of Galileo’s views. In spite of Galileo’s protests, Pope Paul forbade Galileo to hold or defend the heliocentric theory, either orally or in writing. When the Holy Office threatened to bring formal charges if he disobeyed, Galileo—a devout Catholic, reluctantly promised to do so.

Galileo continued to study the heavens privately through his telescope. He also turned his energies to perfecting the microscope and to studying magnets, flood control, condensation of water, navigational problems, and even the chance factors in a roll of dice. He wrote The Assayer
Assayer, The (Galileo) (1623; also known as Saggiatore) and Dialogo sopra i due massimi sistemi del mondo, tolemaico e copernicano (1632; Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican
Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican (Galileo) , 1661). The latter publication, a best-selling book that had been approved by Church censors, presented the witty dialogue of three acquaintances. Each represented a specific posture for and against the scientific and religious worldviews and the debate over the center of the universe, Sun or Earth. On the surface, Galileo treated the three characters impartially. Nevertheless, he cleverly disguised the Aristotelian-Copernican controversy within the dialogue, making sure that the character holding the heliocentric view came off best in the end.

In 1632, when enemies of Galileo pointed out to Pope Urban VIII Urban VIII[Urban 08] (successor to Paul V) that Galileo had violated the 1616 papal order forbidding the discussion of heliocentric theory, Urban immediately stopped the sale of the book and ordered that Galileo be prosecuted for disobedience of a Church order. To make matters worse, Galileo’s enemies claimed that the book ridiculed Church teachings, hinting that one dim-witted character in the book appeared to be the pope himself. To avoid the threat of torture on the rack, Galileo publicly confessed his heresy and the falseness of the heliocentric theory before the pope and the entire Congregation of the Holy Office. Condemned to life imprisonment, never to utter a word about cosmology, the disgraced Galileo saw Dialogue Concerning the Two Chief World Systems prohibited from distribution and burned as trash.

Broken in spirit, arthritic, and confined in isolation to his house outside Florence for the remainder of his life, Galileo spent his later years engaged in pure science, thus avoiding theological speculation. In spite of blindness, Galileo wrote his masterwork, Discorsi e dimostrazioni mathematiche intorno a due nuove scienze atteneti alla meccanica (1638; Discourses Concerning Two New Sciences
Discourses Concerning Two New Sciences (Galileo) , 1914), a book on physics Physics;Europe that provided mathematical proofs on his theory of projectile motion, laws of free-falling bodies, and studies on uniform acceleration and the tensile strength of materials. Somehow, he managed to smuggle the book to the Netherlands for publication. Nearly three decades later, this work by Galileo aided Sir Isaac Newton, Newton, Sir Isaac[Newton, Isaac] an English mathematician, in discovering the laws of gravity and motion.

When Galileo died in 1642, an unforgiving Pope Urban refused to allow the erection of a statue in Galileo’s memory, thus embarrassing the Catholic Church over the next three hundred years for its antiscience and anti-intellectual stance.


In 1835, the Catholic Church finally removed its ban on Galileo’s Dialogue Concerning the Two Chief World Systems, long after the heliocentric theory became accepted science. In 1984, a papal commission released secret documents in the Galileo case and admitted that Galileo should not have been condemned.

Galileo’s continuing fame rests on his mathematical theories, his work in physics, his inventions, and his unsuccessful battles with the Catholic Church. More important, his stature increased over the years because of his stubborn questioning of false ancient beliefs and his demand for verification of “truths” through observation and experimentation. These basic principles, as espoused by Galileo, became the foundation of modern science.

Further Reading

  • Blackwell, Richard J. Galileo, Bellarmine, and the Bible. London: University of Notre Dame Press, 1991. Blackwell’s work examines the complexities of the Galileo affair from the perspective of his contemporary Catholic opponents.
  • Drake, Stillman. Galileo: Pioneer Scientist. Toronto: University of Toronto Press, 1990. A scholarly account that traces Galileo’s journey from Ptolemaic astronomy to full belief in the heliocentric theory.
  • Finocchiaro, Maurice A., ed. The Galileo Affair: A Documentary History. Berkeley: University of California Press, 1989. Provides the actual correspondence of Galileo, his friends, and his enemies from 1613 to 1633. Includes a chronology of events and a biographical glossary.
  • Machamer, Peter, ed. The Cambridge Companion to Galileo. New York: Cambridge University Press, 1998. Collection of essays exploring the many facets of Galileo’s work and his relationship with the Church. Chapter 7 examines “Galileo’s Discoveries with the Telescope and Their Evidence for the Copernican Theory.”
  • Reston, James. Galileo: A Life. New York: HarperCollins, 1994. A lively, dynamic portrayal of Galileo’s life, temperament, and accomplishments.
  • Ronan, Colin A. Galileo. New York: G. P. Putnam’s Sons, 1974. A synthesis of modern scholarship on Galileo’s life in Renaissance Italy. Lavishly illustrated.
  • Rowland, Wade. Galileo’s Mistake: A New Look at the Epic Confrontation Between Galileo and the Church. New York: Arcade, 2003. Rowland argues that Galileo and Church officials disagreed about something more significant than whether Earth revolved around the Sun: He argues that in reality they were in dispute about the nature of truth and how people acquire the truth.
  • Sharratt, Michael. Galileo: Decisive Innovator. Oxford, England: Blackwell, 1994. A concise biography that closely examines Galileo’s masterworks.

Invention of the Telescope

Kepler’s Laws of Planetary Motion

Invention and Development of the Calculus

Galileo Publishes Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican

Huygens Identifies Saturn’s Rings

Cassini Discovers Jupiter’s Great Red Spot

Rømer Calculates the Speed of Light

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Astronomy;heliocentric model of the solar system