Galileo Galilei

Galileo Galilei

Galileo Galilei


Widely regarded as one of the greatest scientists, Galileo Galilei was an Italian astronomer, physicist, engineer and mathematician, who helped shape the scientific revolution during the Renaissance. According to Stephen Hawking, Galileo probably bears more of the responsibility for the birth of modern science than anybody else, and Albert Einstein called him the father of modern science.


He was born in 1564 in Pisa, Italy. He was the eldest of his six siblings. His family belonged to the nobility but was not rich. His father was a well-known musician. In 1574, the family moved to Florence. It was here that Galileo started his formal education at the Camaldolese monastery. He became a novice, intending to join the order of monks, but his father was not pleased with the prospect and instead wanted him to become a medical doctor.

Education, Career and Family

In deference to his father’s wishes, he enrolled for a medical degree at the University of Pisa in 1581. Galileo never seems to have taken medical studies seriously, and started attending courses on his real interests which were in mathematics and natural philosophy. However, due to financial difficulties, he left the university in 1585 without earning his degree.


Galileo continued to study mathematics on his own, meanwhile supporting himself with minor teaching positions.  His application for the chair of mathematics at the University of Bologna was unsuccessful. But he gained a teaching post at the University of Pisa in 1589 based on his descriptions of the hydrostatic principles of weighing small quantities in his book The Little Balance. In 1592 he had to leave the University of Pisa as his contract was not renewed, partly because of estrangement with his colleagues due to his study of falling objects whose findings went against the established Aristotelian principles.


However, he quickly got a position at the University of Padua, where he taught geometry, mechanics and astronomy. He had an 18-year tenure here from 1592 to 1610, and attracted large crowds of followers due to his entertaining lectures.


Although his salary was considerably higher here, his responsibilities as the head of the family, on account of his father’s death in 1591, meant that he was chronically pressed for money. So, he tutored privately well-to-do boarding students to earn additional money. It may have been due to these financial difficulties that he never married though he had a long-term relationship with Marina Gamba, who bore him two daughters and a son.

His Discoveries

In 1609, he learned about a simple telescope built by Dutch eyeglass makers. By trial and error, he figured the secret of the invention and made his own spyglass of 3x magnification from lenses for sale in spectacle makers’ shops. Soon he taught himself the art of lens grinding, and built increasingly powerful telescopes that magnified up to 30 times. Once he turned the telescopes toward the heavens he made some startling discoveries, which he published in a small booklet in 1610, The Starry Messenger. He discovered that the moon was not flat and smooth, but a sphere with mountains and craters. He found that Venus had phases like the moon, implying it revolved around the sun. He also discovered that Jupiter had four revolving moons, which did not revolve around the earth.


Soon Galileo began amassing evidence that supported the Copernican theory of heliocentrism (all planets revolved around the sun) and contradicted the Greek philosopher Aristotle and the Church doctrine that the earth was the center of the universe and everything revolved around it. His observation of the sunspots proved that the sun was not perfect as believed by Aristotle. In 1613, he wrote a letter to a student explaining how Copernican theory did not contradict Biblical passages, stating that Bible was written from an earthly perspective and implied that science provided a different and more accurate perspective. When the letter was made public, the Church Inquisition consultants pronounced that the Copernican theory was heretical, and in 1616 ordered Galileo not to “hold, teach, or defend in any manner” the Copernican theory regarding the motion of the earth. Galileo obeyed the order for seven years, but when a more sympathetic Pope was elected, he wrote a book that seemed to ridicule the Church’s position. Church reacted swiftly, and instituted Inquisition proceedings against Galileo. This led to Galileo being placed under house arrest for the rest of his life.


Galileo theorized that the tides were caused by the sloshing back and forth of water in the seas as a point on the Earth’s surface sped up and slowed down because of the Earth’s rotation on its axis and revolution around the Sun. In this he was mistaken, dismissing as he did then the correct idea held by his contemporary Kepler that the moon caused the tides.


Aristotle and his followers believed that heavier objects fall faster through a medium than lighter ones. Galileo disproved this by dropping a heavy and a light object from the Leaning Tower of Pisa. He also rolled down balls down gently sloping inclined plane to come up with his laws on motion.


Galileo proposed that a falling body would fall with a uniform acceleration, as long as the resistance of the medium through which it was falling remained negligible, or in vacuum. He also derived the correct kinematical law for the distance travelled during a uniform acceleration starting from rest—namely, that it is proportional to the square of the elapsed time. He also concluded that objects retain their velocity unless a force—often friction—acts upon them, refuting the generally accepted Aristotelian hypothesis that objects “naturally” slow down and stop unless a force acts upon them. He also discovered that the time taken for each swing of a pendulum was related to its length and not to its amplitude.


Aside from these contributions, he built a general purpose military compass suitable for use by gunners and surveyors. He also constructed a thermometer. He described an experiment to find the speed of light but could not calculate it satisfactorily. His contributions to mathematics included the method of indivisibles, a forerunner of calculus.


Galileo’s work could be seen as a decisive step towards the eventual separation of science from both philosophy and religion. He sagely remarked that “the grand book of the universe … is written in the language of mathematics”, his own works propelling natural philosophy from a verbal, qualitative account to a mathematical one in which experimentation became a recognized method for discovering the facts of nature.


Galileo was working a way furiously well into his seventies. He became blind towards the end of his life, and passed away in 1642.