Galileo Galilei was an Italian physicist, mathematician, astronomer, andphilosopher who played a major role in the Scientific Revolution.

1564 Galileo Galilei was born on 15 February in Pisa, Italy, the first of six children of Vincenzo Galilei and Giulia Ammannati.

1581 Galileo went to college at the University of Pisa. He began his studies as a medical student, but changed to Mathematics.

1583 During his student days at Pisa, Galileo conducted several experiments with pendulums.

“…the period (the time in which a pendulum swings back and forth) does not depend on the arc of the swing (the isochronism).”

1589 Galileo obtains a teaching position in mathematics at the University of Pisa.

Drawing of pendulum clock designed by Galileo Galilei

•1590 While at the University of Pisa, Galileo disproved existing beliefs that heavier objects fall faster than lighter ones:

“…all objects, regardless of their density, fall at the same rate in a vacuum.”

1590 According to Vincenzo Viviani, Galileo’s first biographer, Galileo demonstrated his conclusions by dropping weights from the leaning tower of Pisa. This report has been doubted by historians.

Apollo 15 Commander Dave Scott demonstrates that the mass of an object does not affect the time it takes to fall, using a hammer and a feather on the Moon. Click the image to view the Google video.

1593 Galileo invents a water lifting machine, a pump driven by horses. He receives a patent for the machine in 1594.

1597 Galileo invents a sector, a calculating instrument consisting of two equal length rulers joined by a hinge. It was used to solve practical mathematics problems in proportion, trigonometry, multiplication and division.

Galilean Sector

1607 Invents a thermoscope, a primitive thermometer that could register variations in temperature.

1609 In early 1609 Galileo built a three-powered telescope based on descriptions of Hans Lipperhey’s invention the previous year. By fall of the same year he had developed an eight-powered telescope.

A replica of the earliest surviving telescope attributed to Galileo Galilei, on display at the Griffith Observatory.

1609 Using this higher-powered telescope, Galileo was the first to observe lunar mountains and craters on Earth’s moon.

1610 In January of 1610, Galileo discovered four satellites in orbit around Jupiter: Io, Europa, Callisto and Ganymede. Initially, he named these Medicean stars after one of his patrons.

Jupiter's four Galilean moons, in a composite image comparing their sizes and the size of Jupiter. From top to bottom: Io, Europa, Ganymede, Callisto.

1610 Galileo was the first person to observe Saturn. Initially, he mistook the rings for planets thinking it was a three-planet system.

1610 Galileo observed that Venus exhibited a full set of phases similar to that of the Moon. The heliocentric model of the solar system

developed by Nicolaus Copernicus predicted that all phases would be visible.

The phases of Venus

1612 Galileo observed the Sun through his telescope and saw that the Sun had dark patches on it (what we now call sunspots). He also

observed the motion of the sunspots indicating that the Sun was rotating on an axis. More evidence of the Copernican heliocentric model of the solar system.

1615 A Dominican friar Niccolo Lorini, who had earlier criticized Galileo's view in private conversations, files a written complaint with the Inquisition against Galileo's Copernican views.

1616 On orders of the Pope Paul V, Cardinal Bellarmine delivered toGalileo 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 that church). For the next several years Galileo stayed well away from the controversy.

1624 Galileo develops a the first known microscope.

1632 Galileo’s book “Dialogue Concerning the Two Chief World Systems” is published. It compares the Copernican (sun-centered) theory of the solar system with the Ptolemaic (Earth-centered) system.

Galilean Microscope

1633 Galileo is summoned to face the Inquisition in Rome. He is convicted of heresy and forced to publicly recant his support of Copernicus. He was sentenced to life imprisonment but because of his advanced age he was allowed to serve his term under house arrest at his villa near Florence.

1642 Galileo died on January 8, 1642.

1992 Pope John Paul II expressed regret for how the Galileo affair was handled, acknowledging the errors committed by the Catholic

Church tribunal that judged Galileo’s scientific positions.The Vatican formally and publicly cleared Galileo of any

wrongdoing.