Galileo Galilei (1564-1642)

When Galileo Galilei was born in 1654, Aristotelian physics primarily defined the known world. The perfect heavens did not change, heavier objects fell faster than lighter objects, and the Earth centered the universe. Galileo’s observations and experiments led to new advances in physics and mathematics; work with pendulums, sectors, and falling bodies laid the groundwork for future discoveries and inventions. Although Galileo is most famous today for his work with telescopes and his observations of the solar system, he was infamous in his own time for his support of the heretical Copernican heliocentrism. By the time of his death in 1642, Galileo Galilei left behind a strong foundation of science that has practical applications today.

Galileo studied at the university in Pisa, and later became a teacher of mathematics. While he may not have actually dropped weights from the tower as the historical myth suggests, in an unpublished book called On Motion Galileo put forth his theory that density determines how fast things fall rather than their weight. After moving to the university in Padua in 1592, Galileo developed the sector and a theory of tidal movement using Copernican theory. He proposed that alterations in the earth’s speed as it rotated on its axis and around the sun caused the tides to move similar to the movement of water in a vase as it was rotated in a similar fashion. During his time at Padua, Galileo began a relationship with Marina Gamba, who would bear him three children: Virginia, who later became known as Sister Maria Celeste, Livia, who later became Sister Arcangela, and Vincenzio, who was later legitimized. 

In 1602, Galileo began investigating pendulums, which had interested him since he was a student in Pisa. He discovered that the amplitude of the pendulum’s swing had no effect on the period of the pendulum; in other words, no matter how high or low a pendulum’s bob was lifted, the time for a full swing remained the same. A physician friend in Venice later put a small pendulum to practical application by using it to measure his patients’ pulse. In 1609, Galileo began building telescopes to observe the heavens and the Moon. By January 1610, Galileo discovered the four satellites of Jupiter that he later named the Medicean Stars in honor of Cosimo d’Medici, which earned him a lifetime position as Chief Mathematician of the University of Pisa and Philosopher and Mathematician to the Grand Duke of Tuscany. Eclipses of these moons will later be used to calculate longitude on land. Galileo’s heliocentric writings on these satellites and his later discoveries of the phases of Venus and sunspots brings him into conflict with the Church, and in 1633 he abjures his errors. He spends the rest of his life in house arrest, where he continues to work on the applications of his theories until his death.

Galileo Galilei’s theories based on direct observation and experimental technique sparked a whole new approach to science that extends to today. The continuation of his work is everywhere, from the pendulum on a clock to the Jupiter spacecraft that bore his name. Galileo has certainly earned his place in history as an icon of science.

The Galileo Project - A detailed set of pages on Galileo’s life, work, and conflict with the Church.

Galileo’s Discoveries - A brief discussion of Galileo’s astronomical discoveries. Includes a fun little quiz.

Galileo Biography - A robust reference list and a set of historical cross-references that place Galileo’s work in context with other scholars.

Galileo Galilei - Multimedia presentations of several of Galileo’s inventions and a recommended tour route when visiting the Tuscany area from The Institute and Museum of the History of Science in Florence, Italy.

NOVA’s Galileo Homepage - The companion page to the NOVA television program with the program’s transcript, teacher guides, interactive experiments, and articles.

Stanford Encyclopedia of Philosophy - Galileo Galilei - Discussion of Galileo’s scientific contributions and Church conflicts.

Galileo’s Vision - An article from Smithsonian Magazine primarily discussing Galileo’s contributions to astronomy.

Galileo and Einstein - The companion page for Physics 109 at the University of Virginia, which includes lecture notes and Galileo’s Dialogue Concerning Two New Sciences.

Trial of Galileo Galilei - A discussion of Galileo’s trial and associated letters and documents.

Galileo Galilei Links - A page of links discussing Galileo Galilei.