---
title: "Galileo Galilei"
chunk: 7/13
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"
---

According to popular legend, after recanting his theory that the Earth moved around the Sun, Galileo muttered the rebellious phrase "And yet it moves". The earliest known written account of the legend dates to a century after his death. Supporting the legend was a claim that a 1640s painting by the Spanish painter Bartolomé Esteban Murillo or an artist of his school, in which the words were hidden until restoration work in 1911, depicts an imprisoned Galileo apparently gazing at the words "E pur si muove" written on the wall of his dungeon. Based on the painting, Stillman Drake wrote "there is no doubt now that the famous words were already attributed to Galileo before his death". However, an intensive investigation by astrophysicist Mario Livio concludes that the supposed Murillo painting is most probably much more recent, a copy of an 1837 Flemish painting by Roman-Eugene Van Maldeghem.
After a period with the friendly Ascanio Piccolomini (Archbishop of Siena), Galileo was allowed to return to his villa at Arcetri near Florence in 1634, where he spent part of his life under house arrest. He was ordered to read the Seven Penitential Psalms once a week for the next three years. However, his daughter Maria Celeste relieved him of the burden after securing ecclesiastical permission to take it upon herself.
While under house arrest, Galileo dedicated his time to one of his finest works, Two New Sciences, a major reason Albert Einstein called Galileo the "father of modern physics". Here he summarised work he had done some forty years earlier, on the two sciences now called kinematics and strength of materials. It was published in Holland to avoid Catholic censorship. Galileo went completely blind in 1638 and developed a painful hernia and insomnia, and he was permitted to travel to Florence for medical advice.

== Scientific contributions ==
This and other facts, not few in number or less worth knowing, I have succeeded in proving; and what I consider more important, there have been opened up to this vast and most excellent science, of which my work is merely the beginning, ways and means by which other minds more acute than mine will explore its remote corners.

=== Scientific methods ===
Galileo made original contributions to the science of motion through an innovative combination of experiments and mathematics. More typical of science at the time were the qualitative studies of William Gilbert, on magnetism and electricity. Galileo's father, Vincenzo Galilei, a lutenist and music theorist, had performed experiments establishing perhaps the oldest known non-linear relation in physics: for a stretched string, the pitch varies as the square root of the tension. These observations lay within the framework of the Pythagorean tradition of music, well known to instrument makers, which included the fact that subdividing a string by a whole number produces a harmonious scale. Thus, a limited amount of mathematics had long related to music and physical science, and young Galileo could see his own father's observations expand on that tradition.
Galileo was one of the first modern thinkers to clearly state that the laws of nature are mathematical. In The Assayer, he wrote "Philosophy is written in this grand book, the universe ... It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures;...." His mathematical analyses are a further development of a tradition employed by late scholastic natural philosophers, which Galileo learned when he studied philosophy. His work marked another step towards the eventual separation of science from both philosophy and religion; a major development in human thought. He was often willing to change his views in accordance with observation.
In order to perform his experiments, Galileo had to set up standards of length and time, so that measurements made on different days and in different laboratories could be compared in a reproducible fashion. This provided a reliable foundation on which to confirm mathematical laws using inductive reasoning. Galileo showed a modern appreciation for the proper relationship between mathematics, theoretical physics, and experimental physics. He understood the parabola, both in terms of conic sections and in terms of the ordinate (y) varying as the square of the abscissa (x). Galileo further asserted that the parabola was the theoretically ideal trajectory of a uniformly accelerated projectile in the absence of air resistance or other disturbances. He conceded that there are limits to the validity of this theory, noting on theoretical grounds that a projectile trajectory of a size comparable to that of the Earth could not possibly be a parabola, but he nevertheless maintained that for distances up to the range of the artillery of his day, the deviation of a projectile's trajectory from a parabola would be only very slight.

=== Astronomy ===

Using his refracting telescope, Galileo observed in late 1609 that the surface of the Moon is not smooth. Early the next year, he observed the four largest moons of Jupiter. Later in 1610, he observed the phases of Venus as well as Saturn, though he thought the planet's rings were two other planets. In 1612, he observed Neptune and noted its motion, but did not identify it as a planet.
Galileo made studies of sunspots, the Milky Way, and made various observations about stars, including how to measure their apparent size without a telescope.
He coined the term Aurora Borealis in 1619 from the Roman goddess of the dawn and the Greek name for the north wind, to describe lights in the northern and southern sky when particles from the solar wind energise the magnetosphere.

=== Engineering ===