Galileo Galilei (15 February 1564 – 8 January 1642) is an Italian physicist, mathematician, astronomer and philosopher who plays a major role in the Scientific Revolution.

His achievements include improvements to the telescope and consequent astronomical observations, and support for Copernicanism.

Galileo has been called the "father of modern observational astronomy," the "father of modern physics," the "father of science," and "the Father of Modern Science."

Stephen Hawking says, "Galileo, perhaps more than any other single person, was responsible for the birth of modern science."

The motion of uniformly accelerated objects, taught in nearly all high school and introductory college physics courses, is studied by Galileo as the subject of kinematics.

His contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the discovery of the four largest satellites of Jupiter (named the Galilean moons in his honor), and the observation and analysis of sunspots.

Galileo also worked in applied science and technology, inventing an improved military compass and other instruments.

Galileo's championing of Copernicanism is controversial within his lifetime, when a large majority of philosophers and astronomers still subscribe at least outwardly) to the geocentric view that the Earth is at the center of the universe.

After 1610, when he begins publicly supporting the heliocentric view, which places the Sun at the center of the universe, he meets with bitter opposition from some philosophers and clerics, and two of the latter eventually denounce him to the Roman Inquisition early in 1615.

In February 1616, although he had been cleared of any offence, the Catholic Church nevertheless condemns heliocentrism as "false and contrary to Scripture", and Galileo is warned to abandon his support for it—which he promises to do.

When he later defends his views in his most famous work, Dialogue Concerning the Two Chief World Systems, published in 1632, he is tried by the Inquisition, found "vehemently suspect of heresy," forced to recant, and spends the rest of his life under house arrest.