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EarthSky // Human World, Science Wire, Space Release Date: Feb 15, 2016

This date in science: Galileo’s birthday

Happy 452nd birthday to one of the first modern scientists, Galileo. With the aid of an early telescope, he helped remove Earth from the center of the universe.

Portrait, attributed to Murillo, of Galileo gazing at the words 'E pur si muove' (not legible in this image) scratched on the wall of his prison cell. Image via Wikimedia Commons.

Portrait, attributed to Murillo, of Galileo gazing at the words ‘E pur si muove’ – ‘And yet it moves’ (not legible in this image) – scratched on the wall of his prison cell. Image via Wikimedia Commons.

February 15, 1564. Italian astronomer, mathematician, and physicist Galileo Galilei was born 452 years ago today. He is one of the first people on Earth to have aimed a telescope at the heavens, where he found – among many other things – phases for the planet Venus, and four starry points of light orbiting the planet Jupiter. In Galileo’s time, educated people subscribed to the Aristotelian view that Earth lay fixed in the center of a more or less unchanging universe. Thus the discovery of moons orbiting Jupiter (now called the Galilean satellites) and revelation that Venus must orbit the sun, not the Earth, were considered heresy by the Roman Inquisition. In 1633, the Inquisition forced Galileo to recant. He spent the rest of his life under house arrest.

Afterwards, famously, he’s said to have said:

E pur si muove (and yet it moves).

The phrase is still used today as a retort, implying it doesn’t matter what you believe; these are the facts.

Galileo grew up in a musical family. In 1574, the family moved to Florence where 18 year-old Galileo began his education in a monastery. He was very successful in his studies, and began studying medicine at the University of Pisa. Due to financial problems, he was unable to finish his degree, but his years at the university were priceless. They introduced him to mathematics, and physics, but most importantly, they introduced him to Aristotle’s philosophy.

Back then, if somebody wished to know about the universe, the way to do it was to read Aristotle’s works. As Dante had put it some centuries before, Aristotle is “the Master of those who know” (Dante, Inferno 4.131). In other words, at that time, knowledge was to philosophy what faith was to religion.

And so, in spite of not being able to complete his degree in medicine and become a university professor, he still continued his studies of mathematics. He was able to get a few minor teaching positions for a living. After two years of hard work, he published La Bilancetta (The Little Balance), his first scientific book which gained him a reputation. The book commented upon the story of how the king of Syracuse asked Archimedes to verify whether his crown was made of pure gold or a mix. Galileo presented an invention of his, the “little balance”, today called “hydrostatic balance”, that is used to make more accurate measurements of differences in density.

Read here about the King’s crown and Archimedes’ other discoveries.

Galileo’s reputation was bruised after the publication of his Du Motu (On Motion), a study of falling objects, which showed his disagreement with the Aristotelian view about the subject.

In 1609, he heard word that in the Netherlands, an instrument that showed distant objects as if they were close by was invented. Like many others, Galileo quickly figured out the mechanics of the spyglass, but he later on greatly improved upon the original design. He presented the Venetian State with an eight-powered telescope – a telescope that magnifies normal vision by eight times. His telescope earned him a doubling of his salary and a life tenure at Padua University.

Over the years, Galileo improved his telescope to magnify up to 20 times.

With his telescope, he made many astronomical discoveries. For example, he was the first to view the moon magnified 20 times. He drew the moon’s surface, showing that its surface is bumpy and rocky, contrary to the popular belief of the time that the moon was smooth.

In January 1610, he discovered the four most massive moons of Jupiter: Io, Europa, Ganymede, and Callisto. Today, they are referred to as the Galilean moons. He lay all of his findings in his book Siderus Nuncius (The Sidereal Messenger).

Galileo observed that Venus went through phases, just as the moon does.

Composite image showing spacecraft views of the four largest moons of Jupiter which are known as the Galilean satellites, first seen by the Italian astronomer Galileo Galilei in 1610. Shown from left to right in order of increasing distance from Jupiter, Io is closest, followed by Europa, Ganymede, and Callisto. Image via NASA.

Composite image showing spacecraft views of the four largest moons of Jupiter which are known as the Galilean satellites, first seen by the Italian astronomer Galileo Galilei in 1610. Shown from left to right in order of increasing distance from Jupiter, Io is closest, followed by Europa, Ganymede, and Callisto. Image via NASA.

Galileo was a very respected man by 1610, but his increasingly public acceptance of the heliocentric system began to cause him trouble with the Roman Catholic Church.

In 1618, Galileo was dragged into a controversy about the nature of comets, which was of no help to his social position. Galileo nevertheless published the argument under his own name in Il Saggitore (The Assayer) in 1623, which is to this day one of his best known pieces of work.

Read selections from The Assayer.

Things didn’t get much better for Galileo until his death in 1642. His work kept defying the accepted Aristotelian view, and earned him the anger of the Roman Catholic Church, which centuries before had founded a group of institutions within the Church’s judicial system – known as the Inquisition – whose whose aim was to combat heresy.

In particular his 1632 publication of his Dialogue Concerning the Two Chief World Systems, Copernican and Ptolemaic opposed the Aristotelian view. In 1633, the Inquisition summoned Galileo to Rome. He was declared a suspect of heresy, was punished by life imprisonment, and was made to abjure formally. Nevertheless, he lived comfortably and was allowed to continue his work.

Galileo never stopped working. In 1634, his beloved elder daughter, Virginia, died. He was 70 years old. He decided to finish what he started before the telescope interrupted him. He collected, and finished his unpublished studies and in 1638 published them in Dialogues Concerning Two New Sciences, discussing kinematics and the properties of materials.

Galileo died on January 8, 1642.

A list of all of Galileo’s discoveries is a very lengthy one. Although Galileo is greatly praised for his various scientific discoveries, he did much more than just push science forward: he also pushed society forward. His life was much more than just a conflict with religion and Aristotelianism. It was a fight against the suppression of the opinion of an emerging scientific minority.

Galileo was one of the first to free science from philosophy. He inspired countless others to pursue the freedom of scientific enquiry.

Portrait of Galileo by Justus Sustermans.  Image via Wikimedia Commons.

Portrait of Galileo by Justus Sustermans. Image via Wikimedia Commons.

Bottom line: Galieo was born on February 15, 1564. He was one of the first to aim a telescope at the heavens.