Galileo Galilei was born in Pisa, Italy, the first of six children to Vincenzo Galilei, a lutenist, composer, and music theorist, and Giulia Ammannati. His early exposure to the arts and intellectual pursuits likely fostered his inquisitive mind and appreciation for mathematical harmony.

While attending the University of Pisa as a medical student, Galileo observed a lamp swinging in the Pisa Cathedral. He noticed that the period of oscillation remained relatively constant regardless of the amplitude, an observation that led him to the principle of isochronism of the pendulum. This later became the basis for pendulum clocks.

Galileo became a professor of mathematics at the University of Pisa. During this period, he began to challenge Aristotelian physics, particularly the prevailing belief that heavier objects fall faster than lighter ones. While the apocryphal story of him dropping objects from the Leaning Tower of Pisa is debated, it represents his commitment to empirical observation.

Galileo accepted a position as professor of mathematics at the University of Padua, a period considered by many to be his most productive. He pursued research in mechanics, hydraulics, and astronomy. This era saw him develop and refine the telescope and began his serious astronomical observations.

Galileo significantly improved the recently invented telescope and began making groundbreaking astronomical observations. He observed the Moon's surface was rough and mountainous, discovered four celestial bodies orbiting Jupiter (now known as the Galilean moons), observed the phases of Venus, and noted sunspots. These discoveries challenged the geocentric (Earth-centered) model of the universe and provided strong evidence for the heliocentric (Sun-centered) model proposed by Nicolaus Copernicus.

Galileo published "Sidereus Nuncius" (Starry Messenger), detailing his telescopic observations. This publication caused a sensation and brought him immediate fame, but also sparked controversy with those who adhered to the traditional Aristotelian worldview.

The Catholic Church officially condemned the heliocentric theory as "false and erroneous." Galileo was warned by Cardinal Robert Bellarmine not to hold or defend Copernican ideas. While not explicitly forbidden from discussing it, he was effectively silenced on the matter.

Galileo published "Dialogue Concerning the Two Chief World Systems," a book presenting arguments for both the geocentric and heliocentric views, but with a clear leaning towards Copernicanism. The book, written in Italian rather than Latin to reach a wider audience, was interpreted as a deliberate defiance of the Church's earlier warning.

Galileo was summoned to Rome to face the Inquisition. After being interrogated and threatened with torture, he was forced to recant his belief in heliocentrism. He was sentenced to house arrest for the remainder of his life. Legend has it that after recanting, he muttered "Eppur si muove" ("And yet it moves"), a defiant affirmation of the Earth's motion, although this is likely apocryphal.

Galileo died under house arrest in Arcetri, near Florence. Despite being blind and restricted in his movements, he continued to write and conduct research until his death. His final work, "Two New Sciences," summarizing his earlier work on motion and mechanics, was smuggled out of Italy and published in the Netherlands in 1638.

Over 350 years after Galileo's death, the Catholic Church, under Pope John Paul II, formally apologized for the errors made in the Galileo affair, acknowledging that Galileo was correct in his advocacy of heliocentrism. This marked a significant turning point in the relationship between science and religion.