Portrait, attributed to Murillo, of Galileo looking 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.
Congratulations on the birthday of the Italian astronomer, mathematician and physicist Galileo Galilei, born on February 15, 1564. Galileo was one of the first to point a telescope at the night sky, where he saw the phases of Venus and four dots of light. orbiting Jupiter (now known as Jupiter’s famous Galilean moons). These and other observations have begun to change the way we have seen the universe, and our place in it.
In Galileo’s time, educated people endorsed the Aristotelian view that the earth lay fixed in the middle of a more or less immutable universe. His discovery of moons orbiting Jupiter (now known as the Galilean satellites in his honor) and the phases of Venus due to the planet orbiting the sun is considered heresy by the Roman Inquisition. In 1633, these tribunals – developed by the Holy See of the Roman Catholic Church – forced Galileo to withdraw.
When he left the courtroom, he was said to have muttered:
E pur si muove (and yet it moves).
And so does it. The earth moves and all objects move in space. The phrase is still used today as an answer, which implies it does not matter what you believe; these are the facts.
Galileo spent the rest of his life under house arrest, but that did not stop him from publishing another work, Two New Sciences, on mechanics and motion.
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Galileo grew up in a musical family. In 1574, the family moved to Florence, where 18-year-old Galileo began training in a convent. He was very successful in his studies and started studying medicine at the University of Pisa. Due to financial difficulties, he could not complete his degree, but his years at the university were invaluable. They introduced him to mathematics and physics, but most importantly, they introduced him to Aristotle’s philosophy.
Back then, if anyone wanted to know about the universe, the way to do that was to read Aristotle’s works. As Dante put it a few centuries earlier, Aristotle is ‘the master of those who know’ (Dante, Inferno 4.131). In other words, at that time, knowledge of philosophy was faith for religion.
Despite not being able to complete his degree in medicine and become a university professor, Galileo continued his studies in mathematics. He was able to get some minor teaching positions for his existence. After two years of hard work, he publishes ‘La Bilancetta’ (The small balance), his first scientific book, which earned him a reputation. The book commented on the story of how the king of Syracuse asked Archimedes to verify whether his crown was of pure gold or a mixture of metals of lower value. Galileo presented an invention of his, the ‘little balance’, today called ‘hydrostatic balance’, which is used to make more accurate measurements of the differences in density.
Read here about the royal crown and Archimedes’ other discoveries.
Galileo’s reputation was ruined after the publication of his “Du Motu” (On Motion), a study of falling objects, which showed that he did not agree with the Aristotelian view on the subject.
In 1609 he heard that in the Netherlands an instrument had been invented which displayed distant objects as if they were near. Like many others, Galileo quickly realized the mechanics of the mirror glass, but later significantly improved the original design. He powered the Venetian state a telescope of eight, a telescope that magnifies the normal vision eight times. His telescope earned him a doubling of his salary and a life span at Padua University.
Over the years, Galileo has enlarged its telescope to 20 times.
One of Galileo’s telescopes. Image via University of Oregon.
With his telescope he made many astronomical discoveries. For example, he was the first to see the moon magnified 20 times. He drew the moon’s surface and showed that the surface was bumpy and rocky, contrary to the general notion 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 set out all his findings in his book “Sidereus Nuncius” (The Starry Messenger).
Galileo notices that Venus, like the moon, goes through phases.
Composite image showing spacecraft views of Jupiter’s four largest moons. The Italian astronomer Galileo Galilei, known as the Galilean satellites, was first seen in 1610. Shown from left to right in order of increasing distance from Jupiter. Io is the closest, followed by Europa, Ganymede and Callisto. Image via NASA.
Galileo was a 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 is dragged into a controversy over the nature of comets, which does not help his social position. Galileo nevertheless published the argument under his own name in “Il Saggitore” (The claimant) in 1623, which to this day is one of his most famous pieces.
Read the choices from “The Assayer”.
Things did not get much better for Galileo before his death in 1642. His work constantly challenged the accepted Aristotelian view and angered the Roman Catholic Church, which established a group of institutions within the ecclesiastical legal system – known as the Inquisition – whose aim was to combat heresy.
The Aristotelian view was particularly opposed in his 1632 publication of his “Dialogue Concerning the Two Chief World Systems, Copernican and Ptolemaic”. In 1633, the Inquisition summoned Galileo to Rome. He was declared a suspect in heresy, was sentenced to life in prison and was formally brought to his side. Nevertheless, he lived comfortably and was allowed to continue his work.
Galileo’s daughter, Sister Maria Celeste, was a nun in the Catholic Church. They regularly wrote letters to each other and she stored the letters Galileo wrote to her, which were finally published in 1999 in a book by Dava Sobel called Galileo’s Daughter.
Despite Galileo’s battles with the church, he was a devout Catholic. He will probably be happy to know that the Vatican now has its own observatory and that some of its fathers are astronomers. But it was not until 1992 that the Vatican acknowledged that Galileo was right in his heliocentric beliefs.
Galileo died on January 8, 1642.
A list of all Galileo’s discoveries is long. Although Galileo is highly praised for his various scientific discoveries, he has done much more than just push science forward: he has also propelled society forward. His life was much more than just a conflict with religion and Aristotelianism. It was a struggle against the suppression of the opinion of an emerging scientific minority.
Galileo was one of the first to liberate science from philosophy. He inspired many others to pursue the freedom of scientific inquiry.
Portrait of Galileo by Justus Sustermans. Image via Wikimedia Commons.
In short: One of our greatest astronomers, Galileo Galilei, was born on February 15, 1564. His discoveries with the improved telescopes he made changed the way we view the universe.
