Galileo Galilei - Biographical Profile

Portrait of Galileo Galilei, painted by Justus Sustermans in 1636. Public domain through Wikimedia Commons

Galileo Galilei - Basic Information:

Nationality: Italian

Religion: Roman Catholic

Born: February 15, 1564
Death: January 8, 1642

Children (with mistress Marina Gamba):

  • Virginia, 1600
  • Livia, 1601
  • Vincenzio, 1606

Education and Academic Positions:

Born in Pisa to Vincenzo Galilei, a famous lutenist and musical theorist, Galileo was a devout Catholic who seriously considered pursuing a career in the priesthood.

Instead, at his father's urging, he enrolled at the University of Pisa to study medicine, but switched to mathematics. He was appointed the chair of mathematics in 1589. In 1592 he moved to the University of Padua, teaching in the fields of mathematics, geometry, and astronomy until 1610.

Galileo - the Father of Science:

Among other things, Galileo has been called:

  • The father of science (by Albert Einstein)
  • The father of modern physics
  • The father of modern astronomy
  • The father of observational science

Stephen Hawking (among others) have observed that Galileo probably contributed more to the creation of the modern natural sciences, and the scientific method, than any other single figure in history.

Specifically, Galileo focused on observation and experimentation, rather than creating abstract theories that were not tested. He also was one of the first scientists to provide mathematical descriptions of the laws of physics.


Some of Galileo's most significant work was in the field of kinematics, identifying that the total distance covered is proportional to the square of the time. He also identified the parabola as the ideal trajectory for uniformly accelerated motion in a plane.

Galileo also studied the motion of a pendulum, realizing that a pendulum swing is constant regardless of amplitude (at least to small angle approximations).

He proposed a principle of inertia, which became the foundation of Newton's First Law of Motion. Though this concept had been put forth by others, Galileo was the first to formalize it mathematically.

Astronomy, the Telescope, & the Heliocentric Universe:

In 1608, the telescope was invented in the Netherlands. Over the next year, Galileo had heard about it and crafted his own improvements. With the improved telescope, he was able to observe the heavens more closely than ever before and identified three of Jupiter's moons. This, along with observing the phases of Venus, provided support for the Copernican heliocentric model of the universe over Ptolemy's geocentric model.

In addition, he made many other significant observations. He was the first to observe sunspots, the rings of Saturn (though he didn't know what to make of him), and lunar mountains and craters.

Galileo's First Controversy:

Galileo's support of a heliocentric theory was seen by the Roman Catholic Church as contradicting various scriptural passages.

In 1616, Galileo first defended himself against the Church. Galileo was ordered not to "hold or defend" the idea that the Earth moved and the Sun remained stationary at the center.

For several years, Galileo was able to discuss heliocentric theory hypothetically without arousing undue ire from the Church.

Galileo's Trial:

In 1632, Galileo published Dialogue Concerning the Two Chief World Systems with the permission of Pope Urban VII, who had supported Galileo in the earlier conflict (as Cardinal Barberini). Urban had two conditions:

  1. Galileo was to include arguments for both heliocentric and geocentric viewpoints
  2. Urban's own views on the matter were to be included

Unfortunately, the book turned out to be biased in favor of heliocentrism and the Pope did not appreciate the perceived public ridicule.

Galileo was ordered to stand trial for suspicion of heresy in 1633.

Galileo's Imprisonment:

The 1633 hearing did not go as well as the one in 1616, and Galileo was found guilty of heresy.

His sentence had three parts:

  • He was required to recant his heliocentric views
  • He was imprisoned (though this later got commuted to house arrest at his estate near Florence)
  • His Dialogue was banned, and all other works written by him (or to be written by him) were forbidden, though this latter part was not enforced.

While under house arrest, Galileo wrote Two New Sciences, which outlined his earlier work in kinematics and the strength of materials. This book was praised by both Sir Isaac Newton and Albert Einstein.

Galileo's Death & Redemption:

Galileo died of natural causes in 1642, after having gone blind.

He was reburied at Santa Croce, sacred ground, in 1737. In 1741, Pope Benedict XIV authorized publication of Galileo's complete works. Heliocentrism was formally rescended as heresy in 1758.

It was not until October 31, 1992, that the Church under Pope John Paul II expressed regret over how Galileo had been treated, in response to a Pontifical Council for Culture study.

Galileo Galilei is one of the most influential and famous scientists in human history, having contributed to a wide range of fields and establishing the mathematical and experimental foundations of modern physics and astronomy.