Move to Florence
Galileo moves with his family from Pisa to Florence, where his early education continues.
Astronomer profile · World History Database
Galileo Galilei
Galileo Galilei helped establish telescopic observation as a powerful method in astronomy. Beginning in 1609, he improved the telescope and used it to examine the Moon, the satellites of Jupiter, the phases of Venus, sunspots and the Milky Way.
Why Galileo Galilei matters in astronomy
These observations did not by themselves prove every part of the Copernican model, but they undermined important assumptions of traditional cosmology and demonstrated that the heavens could be investigated through instruments and repeated observation.
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Galilei, GalileoName2, Name1 format
Galileo Galilei timeline in the database
University of Pisa Enrollment
Galileo enrolls in the Faculty of Arts at the University of Pisa.
Mathematics Chair at Pisa
Galileo is appointed to the chair of mathematics at the University of Pisa.
Pisa Inaugural Lecture
Galileo delivers his inaugural university lecture before beginning regular mathematics teaching at 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.
Dialogue on the New Star
Galileo is thought to co-author a satirical dialogue attacking Aristotelian interpretations of the new star.
Copernican System
Publication of "The Starry Messenger", claims the Earth revolves around the Sun. Galileo's observations of the phases of Venus proved that it orbited the Sun and lent support to (but did not prove) the heliocentric model
Discovery of Lunar Light
Discovers Lunar Reflected Light
Discovery of Moon
Uses the newly invented telescope to discover mountains & continents on the moon
Discovery of Saturn
The first observation of Saturn through a telescope is made by Galileo Galilei, his first telescope is so crude that he wasnt able to distinguish the planets rings; instead he thought the planet might have ears or two large moons on either side
Discovery of Venus
Galileo's observations of the phases of Venus proved that it orbited the Sun and lent support to (but did not prove) the heliocentric model. Galileo observes that Venus exhibited a full set of phases similar to that of the Moon
Invention of Telescope
Publishes his initial telescopic astronomical observations in March 1610 in a short treatise entitled Sidereus Nuncius (Starry Messenger)
Sidereus Nuncius
Publishes his initial telescopic astronomical observations in March 1610 in a short treatise entitled Sidereus Nuncius (Starry Messenger). Publication of "The Starry Messenger", claims the Earth revolves around the Sun
Sunspots
Discovers that Sunspots move across the surface of the sun
Milky Way Resolved into Stars
Galileo reports that telescopic observation resolves the Milky Way into a vast multitude of individual stars.
Medicean Stars Named
Galileo names Jupiter's newly discovered satellites the Medicean Stars in honour of the ruling Medici family.
Appointment as Grand Ducal Mathematician
Galileo becomes mathematician and philosopher to Grand Duke Cosimo II, allowing his return from Padua to Tuscany.
First Telescopic Observation of Jovian Satellites
Observes three points of light close to Jupiter, beginning the discovery of its major moons.
Discovery of Callisto
Observes the fourth Galilean moon, later named Callisto.
Jovian Moons Recognized as Satellites
Concludes that four observed bodies orbit Jupiter rather than the Earth.
Sidereus Nuncius
Publishes telescopic observations of Jupiter's satellites in Sidereus Nuncius.
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.
Discovery of Neptune
Galileo also observed the planet Neptune in 1612, but did not realize that it was a planet
Sunspots
Previous sunspot observations had been misinterpreted as planetary transits, until Galileo gave the correct explanation in 1612
Copernican System
Published in "letters on the solar spots". For Galileo, the tides were caused by the sloshing back and forth of water in the seas as a point on the Earths surface speeded up and slowed down because of the Earths rotation on its axis and revolution around the Sun. Attempts to show there is scriptural support for his beliefs but condemned by the Pope
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.
Letter to Christina of Lorraine
Galileo completes a major letter discussing the proper relationship between scientific inquiry and interpretation of Scripture.
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.
Copernican System
Galileo circulates his first account of the tides in 1616, addressed to Cardinal Orsini. Cardinal Bellarmine, acting on directives from the Inquisition, delivered an order not to "hold or defend" the idea that the Earth moves and the Sun stands still at the centre
Bellarmino Admonition
Cardinal Bellarmino formally admonishes Galileo not to hold or defend the Copernican doctrine.
Copernican System
Galileo revives his project of writing a book about heliocentrism, encouraged by the election of Cardinal Barberini as Pope Urban VIII in 1623
The Assayer Published
Galileo publishes The Assayer, presenting influential arguments about mathematical description and the investigation of natural phenomena.
Two Chief World Systems
Publication of "Two Chief World Systems", claims the Earth revolves around the Sun
Residence at Il Gioiello
Galileo rents the villa Il Gioiello at Arcetri, near the convent where his daughters live.
Copernican System
The book, Dialogue Concerning the Two Chief World Systems, is published in 1632, with formal authorization from the Inquisition and papal permission. By the inquisition, forced to deny his belief in the Copernican system
Dialogue Concerning the Two Chief World Systems
The book, Dialogue Concerning the Two Chief World Systems, is published in 1632, with formal authorization from the Inquisition and papal permission
Trial
By the inquisition, forced to deny his belief in the Copernican system
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.
Arrest of Galilei Galileo
Placed under House arrest
Trial
Sentenced to life imprisonment, commuted to house arrest
Galileo Abjuration
Galileo is formally condemned and required to sign an abjuration of the Copernican position.
Return to Arcetri
The Holy Office permits Galileo to return to his villa at Arcetri while maintaining restrictions on his contacts and scientific discussion.
Discovery of Lunar Libration
Discovers Lunar libration
Death of Galilei Galileo
Death of Galilei Galileo
Trial
John Paul II orders an inquiry into the Church's treatment of Galileo
Trial
The Vatican admits that it was mistaken in its treatment of Galileo
Related astronomy topics
Sources and editorial provenance
Compiled and edited by World History Database
Historical chronology compiled from the World History Database and checked against major scientific and historical reference sources.
Last reviewed: September 2026.
- Royal Museums Greenwich — History of astronomy
- Royal Museums Greenwich — History of the telescope
- NASA Science — Hubble timeline
- NASA Science — Exoplanet discovery history
- LIGO — GW150914 first gravitational-wave detection
- Event Horizon Telescope — first black-hole image
- NASA Webb — mission science and discoveries