Galileo Galilei Biography and Timeline

Move to Florence

Galileo moves with his family from Pisa to Florence, where his early education continues.

University of Pisa Enrollment

Galileo enrolls in the Faculty of Arts at the University of Pisa.

Pendulum Isochronism Observation

Galileo observes the regularity of a swinging cathedral lamp, an episode later associated with his investigations of pendulum motion.

Study of Euclidean Geometry

Galileo begins serious study of Euclid under Ostilio Ricci, strengthening the mathematical foundation of his later scientific work.

Pisa Inaugural Lecture

Galileo delivers his inaugural university lecture before beginning regular mathematics teaching at Pisa.

Mathematics Chair at Pisa

Galileo is appointed to the chair of mathematics at the University of Pisa.

Mathematics Chair at Padua

The Venetian Senate appoints Galileo professor of mathematics at the University of Padua.

Padua Inaugural Lecture

Galileo gives his inaugural lecture at Padua, beginning eighteen productive years in the Venetian Republic.

Letter to Kepler on Copernicanism

Galileo writes to Johannes Kepler describing himself as a long-standing supporter of the Copernican system.

Geometric and Military Compass

Galileo develops a sophisticated geometric and military compass for practical mathematical calculations.

Law of Chords

In the same letter, Galileo formulates the law of chords concerning descent times along chords of a vertical circle.

Pendulum Isochronism Letter

Galileo writes to Guidobaldo del Monte describing his principle that pendulums of equal length have approximately equal periods.

Dialogue on the New Star

Galileo is thought to co-author a satirical dialogue attacking Aristotelian interpretations of the new star.

Operations of the Geometric Compass

Galileo publishes instructions explaining the mathematical and practical uses of his geometric and military compass.

Defence of the Geometric Compass

Galileo publishes a defence of his geometric compass against claims that Baldassarre Capra had originated the instrument.

Telescope Magnification Improved

After learning of the Dutch telescope, Galileo rapidly improves the design until his best instruments exceed twenty-power magnification.

First Telescopic Observation of Jovian Satellites

Observes three points of light close to Jupiter, beginning the discovery of its major moons.

Role range: 1564-1642

Discovery of Callisto

Observes the fourth Galilean moon, later named Callisto.

Role range: 1564-1642

Jovian Moons Recognized as Satellites

Concludes that four observed bodies orbit Jupiter rather than the Earth.

Role range: 1564-1642

Sidereus Nuncius

Publishes telescopic observations of Jupiter's satellites in Sidereus Nuncius.

Role range: 1564-1642

Appointment as Grand Ducal Mathematician

Galileo becomes mathematician and philosopher to Grand Duke Cosimo II, allowing his return from Padua to Tuscany.

Medicean Stars Named

Galileo names Jupiter's newly discovered satellites the Medicean Stars in honour of the ruling Medici family.

Milky Way Resolved into Stars

Galileo reports that telescopic observation resolves the Milky Way into a vast multitude of individual stars.

Jovian Moon Period Studies

Galileo begins systematic study of the orbital periods of Jupiter's four large moons.

Longitude Method Using Jovian Moons

Galileo proposes using predicted eclipses of Jupiter's moons as a celestial clock for determining longitude.

Rome Telescope Demonstrations

Galileo demonstrates telescopic observations in Rome, strengthening recognition of the instrument's astronomical value.

Micrometer for Jovian Moons

Galileo develops a micrometer to improve measurements of the apparent separations of Jupiter's moons.

Discourse on Floating Bodies

Galileo publishes a discourse defending Archimedean hydrostatics against Aristotelian explanations of why bodies float or sink.

Letter to Benedetto Castelli

Galileo writes to Benedetto Castelli arguing that scriptural interpretation should not override demonstrated conclusions about the natural world.

Caccini Attack on Copernicanism

Galileo becomes the target of a public sermon by Tommaso Caccini attacking Copernican astronomy and mathematicians.

First Letter to Piero Dini

Galileo writes to Piero Dini defending Copernican astronomy and arguing that it need not conflict with Scripture.

Second Letter to Piero Dini

Galileo sends another letter to Piero Dini continuing his defence of Copernican astronomy.

Letter to Christina of Lorraine

Galileo completes a major letter discussing the proper relationship between scientific inquiry and interpretation of Scripture.

Bellarmino Admonition

Cardinal Bellarmino formally admonishes Galileo not to hold or defend the Copernican doctrine.

The Assayer Published

Galileo publishes The Assayer, presenting influential arguments about mathematical description and the investigation of natural phenomena.

Magnet Armature Experiments

Galileo reports experiments in which an iron armature greatly increases the lifting strength of a magnet.

Residence at Il Gioiello

Galileo rents the villa Il Gioiello at Arcetri, near the convent where his daughters live.

Dialogue Presented to Grand Duke

Galileo presents his newly published Dialogue Concerning the Two Chief World Systems to Grand Duke Ferdinando II.

Summoned by the Inquisition

The Florentine Inquisitor orders Galileo to appear before the Holy Office in Rome over the Dialogue.

Galileo Abjuration

Galileo is formally condemned and required to sign an abjuration of the Copernican position.