Galileo Galilei was born on February 15, 1564, in Pisa, Italy.¹⁾

He was the first of six children born to Vincenzo Galilei, a musician and music theorist, and Giulia Ammannati.²⁾

Galileo initially studied medicine at the University of Pisa but later shifted his focus to mathematics and physics.³⁾

His experiments with pendulums led to his discovery of the isochronism of pendulums, meaning that the period of a pendulum's swing is constant regardless of its amplitude.⁴⁾

In 1609, Galileo heard about the invention of the telescope and built his own version, greatly improving its design.⁵⁾

With his telescope, Galileo discovered the four largest moons of Jupiter, now known as the Galilean moons: Io, Europa, Ganymede, and Callisto.⁶⁾

He observed the phases of Venus, which supported the heliocentric model proposed by Nicolaus Copernicus.⁷⁾

Galileo's observations of the Moon revealed its rough and mountainous surface, challenging the traditional belief in a perfectly smooth celestial body.⁸⁾

In 1610, he published “Sidereus Nuncius” (Starry Messenger), describing his astronomical discoveries.⁹⁾

His observations of the Milky Way challenged the idea that it was composed of a multitude of stars too faint to see individually.¹⁰⁾

Galileo's work on the pendulum and the law of falling bodies laid the groundwork for Isaac Newton's theory of universal gravitation.¹¹⁾

He formulated the principle of relativity for uniform motion, a precursor to Albert Einstein's theory of special relativity.¹²⁾

Galileo was a proponent of the Copernican heliocentric model of the solar system, which placed the Sun at the center.¹³⁾

His support for the heliocentric model put him at odds with the Catholic Church, which adhered to the geocentric model.¹⁴⁾

In 1616, the Catholic Church issued a decree prohibiting the teaching of Copernicanism, leading Galileo to be cautious about his views.¹⁵⁾