---
title: "Galileo Galilei"
chunk: 1/13
source: "https://en.wikipedia.org/wiki/Galileo_Galilei"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:02:33.342669+00:00"
instance: "kb-cron"
---

Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642), commonly referred to as Galileo Galilei, was an Italian astronomer, physicist, and engineer, sometimes described as a polymath. He was born in the city of Pisa, then part of the Duchy of Florence. Galileo has been called the father of observational astronomy, modern-era classical physics, the scientific method, and modern science.
Galileo studied speed and velocity, gravity and free fall, the principle of relativity, inertia, projectile motion, and also worked in applied science and technology, describing the properties of the pendulum and "hydrostatic balances". He was one of the earliest developers of the thermoscope and the inventor of various military compasses. With an improved telescope he built, he observed the stars of the Milky Way, the phases of Venus, the four largest satellites of Jupiter, Saturn's rings, lunar craters, and sunspots. He also built an early microscope.
Galileo's championing of Copernican heliocentrism was met with opposition from within the Catholic Church and from some astronomers. The matter was investigated by the Roman Inquisition in 1615, which concluded that his opinions contradicted accepted Biblical interpretations.
Galileo later defended his views in Dialogue Concerning the Two Chief World Systems (1632), which appeared to dispute and satirize Pope Urban VIII, thus alienating both the Pope and the Jesuits, who had both strongly supported Galileo until this point. He was tried by the Inquisition, found "vehemently suspect of heresy", and forced to recant. He spent the rest of his life under house arrest. During this time, he wrote Two New Sciences (1638), primarily concerning kinematics and the strength of materials.

== Early life and family ==
Galileo was born in Pisa (then part of the Duchy of Florence) on 15 February 1564, the first of six children of Vincenzo Galilei, a leading lutenist, composer, and music theorist, and Giulia Ammannati, the daughter of a prominent merchant, who had married two years earlier in 1562, when he was 42 and she was 24. Galileo became an accomplished lutenist himself.
Three of Galileo's five siblings survived infancy. The youngest, Michelangelo (or Michelagnolo), also became a lutenist and composer who added to Galileo's financial burdens for the rest of his life. Michelangelo was unable to contribute his fair share of their father's promised dowries to their brothers-in-law, who later attempted to seek legal remedies for payments due. Michelangelo also occasionally had to borrow funds from Galileo to support his musical endeavours and excursions. These financial burdens may have contributed to Galileo's early desire to develop inventions that would bring him additional income.
When Galileo Galilei was eight, his family moved to Florence, but he was left under the care of Muzio Tedaldi for two years. When Galileo was ten, he left Pisa to join his family in Florence, where he came under the tutelage of Jacopo Borghini. He was educated, particularly in logic, from 1575 to 1578 in the Vallombrosa Abbey, about 30 km (19 mi) southeast of Florence.

=== Name ===
Galileo tended to refer to himself only by his first name. At the time, surnames were optional in Italy, and his first name had the same origin as his sometimes-family name, Galilei. Both his given and family name ultimately derived from an ancestor, Galileo Bonaiuti, an important physician, professor, and politician in Florence in the 15th century. When he did refer to himself with more than one name, it was sometimes as Galileo Galilei Linceo, a reference to his being a member of the Accademia dei Lincei, an elite science organization founded in the Papal States. It was common for mid-16th century Tuscan families to name the eldest son after the parents' surname. Hence, Galileo Galilei was not necessarily named after his ancestor Galileo Bonaiuti. 
The Italian male given name "Galileo" (and thence the surname "Galilei") derives from the Latin "Galilaeus", meaning "of Galilee". This biblical name became the subject of a (supposed) pun. In 1614, during the Galileo affair, one of Galileo's opponents, the Dominican priest Tommaso Caccini, delivered against Galileo a controversial and influential sermon quoting the Book of Acts: "Ye men of Galilee, why stand ye gazing up into heaven?".

=== Children ===

Though a pious Catholic, Galileo fathered three children out of wedlock with Marina Gamba: daughters Virginia (b. 1600) and Livia (1601), and a son Vincenzo (1606).
Due to their illegitimate birth, Galileo considered the girls unmarriageable, requiring expensive support or exorbitant dowries, similar to Galileo's previous financial problems with two of his sisters. Their only respectable alternative was the religious life: they became lifelong nuns in the convent of San Matteo in Arcetri.
Virginia took the name Maria Celeste upon entering the convent. She died on 2 April 1634, and is buried with Galileo at the Basilica of Santa Croce, Florence. Livia took the name Sister Arcangela and was ill most of her life. Vincenzo was later legitimised as  Galileo's legal heir, and married Sestilia Bocchineri.