Galileo Galilei Timeline

After hearing reports of Hans Lippershey's spyglass in the Netherlands, Galileo quickly constructed his own improved version without seeing one firsthand. Within weeks he created telescopes magnifying up to around 20 times.

Image source: History of the telescope

Galileo demonstrated the military value of his telescope to the Venetian Senate by allowing officials to spot approaching ships hours before they became visible to the naked eye. He was rewarded with a doubled salary and lifetime tenure at Padua.

Image source: Republic of Venice

Galileo turned his telescope toward the Moon and discovered that its surface was rough and mountainous rather than perfectly smooth, directly contradicting Aristotelian cosmology. His drawings documented craters, mountains, and lunar valleys.

Image source: Sidereus Nuncius

Over successive nights, Galileo observed three, then four 'stars' moving near Jupiter, concluding they were moons orbiting the planet. This discovery provided powerful evidence that not all celestial bodies orbited Earth.

Image source: Galilean moons

Galileo announced his telescopic discoveries — including the Moon's surface, Jupiter's moons, and countless stars of the Milky Way — in Sidereus Nuncius. The work brought him instant fame across Europe.

Naming Jupiter's moons the 'Medicean Stars' in honor of his former pupil, Grand Duke Cosimo II, Galileo secured an appointment as First Mathematician and Philosopher to the Grand Duke of Tuscany and returned to Florence.

Image source: Cosimo II de' Medici

Galileo discovered that Venus displays a full set of phases like the Moon, evidence consistent with the heliocentric model of Copernicus and inconsistent with the pure geocentric Ptolemaic system.

Image source: Phases of Venus

Galileo made systematic observations of sunspots, demonstrating that the Sun was not perfect and unchanging, and that it rotated. His findings led to a bitter priority dispute with the Jesuit astronomer Christoph Scheiner.

Image source: Sunspot

While charting the motions of Jupiter's moons, Galileo recorded Neptune as a dim star, making him one of the first humans to observe the planet — more than two centuries before its formal discovery in 1846.

Image source: Discovery of Neptune

In response to questions raised after a dinner conversation with Grand Duchess Christina, Galileo argued that Scripture teaches how one goes to heaven, not how heaven goes, asserting the independence of scientific inquiry from literal biblical interpretation.

Galileo circulated a lengthy letter elaborating his views on the relationship between science and Scripture, arguing that biblical passages should not be read literally when they conflict with proven scientific truths.

Image source: Letter to the Grand Duchess Christina

Galileo went to Rome to advocate for the Copernican cause before Church authorities. Although warmly received initially, his campaign prompted a theological commission to examine Copernicanism.

Image source: Galileo affair

A Church commission declared heliocentrism formally heretical, and Copernicus's De revolutionibus was suspended pending correction. Galileo was personally instructed by Cardinal Bellarmine not to hold or defend the Copernican view.

Image source: Index Librorum Prohibitorum

Galileo's Dialogue compared the Ptolemaic and Copernican systems through three characters over four days of discussion. The apparent advocacy of heliocentrism, despite papal warnings, provoked outrage in Rome.

Image source: Dialogue Concerning the Two Chief World Systems

The Dialogue was placed on the Index, and Galileo was condemned to permanent house arrest, initially at the residence of Archbishop Piccolomini in Siena and then at his villa in Arcetri near Florence.

Under threat of torture, the aged Galileo stood trial before the Inquisition, was found 'vehemently suspect of heresy,' and forced to recant heliocentrism. Legend holds he muttered 'Eppur si muove' — 'And yet it moves.'

Maria Celeste, Galileo's beloved eldest daughter who had been his closest confidante and caretaker during his trials, died at the convent of San Matteo, plunging him into deep grief.

Image source: Maria Celeste

Despite his condemnation and failing eyesight, Galileo completed his greatest scientific work, Two New Sciences, summarizing decades of research on kinematics and material strength. It was smuggled out and published in Leiden by Elzevir, outside Church jurisdiction.

Image source: Two New Sciences

Years of observing the Sun contributed to Galileo losing his sight entirely. He famously lamented that the universe he had enlarged a thousandfold had now shrunk to the narrow confines of his own body.

During his Italian tour, the young English poet John Milton visited Galileo under house arrest, an encounter later referenced in Areopagitica; Galileo appears in Milton's Paradise Lost as the only contemporary mentioned.

Image source: John Milton

Galileo died at age 77 at Villa Il Gioiello in Arcetri, still under house arrest. The Grand Duke wished to bury him in Santa Croce with honors, but Church authorities objected; he was interred in a modest room until a monumental tomb was erected there nearly a century later, in 1737.