Portrait, attributed to Murillo, of Galileo looking at the words “E pur si muove” (“However, he moves;” not readable in this image) scratched on the wall of his prison cell. Image via Wikimedia Commons.
Happy 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 phases of Venus and four points of light orbiting around Jupiter (now known as the famous Galilean moons of Jupiter). These and other observations began to change the way we view the universe and our place in it.
In the time of Galileo, educated people subscribed to the Aristotelian view that the Earth was fix at the center of a more or less immutable universe. So their discovery of moons orbiting Jupiter (now known as satellites of Galilee in his honor) and the resulting phases of Venus from the planet orbiting the sun were considered heresies by the Roman Inquisition. . In 1633, these courts, which had been developed by the Holy See of the Roman Catholic Church, forced Galileo to retire.
As he left the room, he is said to have murmured:
It’s pure if it moves (and it still moves).
And so it does. The Earth moves and all objects in space move. The phrase is still used today as a replica, which implies it doesn’t matter what you believe; these are the facts.
Galileo spent the rest of his life under house arrest, but this 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 Galileo, 18, 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 in college were priceless. He was introduced to mathematics and physics, but most importantly, he was introduced to the philosophy of Aristotle.
Then, if anyone wanted to know the universe, the way to do it was to read the works of Aristotle. As Dante had said a few centuries earlier, 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.
Thus, despite not being able to finish his medical degree and become a university professor, Galileo continued his studies in mathematics. He was able to get some minor teacher positions to make a living. After two years of hard work, he published “La Bilancetta” (The little balance), his first scientific book, which gained him fame. The book told the story of how the king of Syracuse asked Archimedes to check if his crown was pure gold or a mixture of lesser precious metals. Galileo presented an invention of his, the “small equilibrium”, today called “hydrostatic equilibrium”, which is used to make more accurate measurements of density differences.
Read here about the king’s crown and Archimedes’ other discoveries.
Galileo’s reputation died after the publication of his “Du Motu” (Moving), a study of falling objects, which showed his disagreement with the Aristotelian view on the subject.
In 1609, he learned that an instrument had been invented in the Netherlands that showed distant objects as if they were close. Like many others, Galileo quickly discovered the mechanics of the spike lens, but later greatly improved the original design. He introduced to the Venetian state an eight-motor telescope, a telescope that magnifies normal vision eight times. His telescope earned him twice his salary and his stay at the University of Padua.
Over the years, Galileo improved his telescope to magnify up to 20 times.
One of Galileo’s telescopes. Image through the University of Oregon.
With his telescope, he made many astronomical discoveries. For example, he was the first to see the moon rise 20 times. He drew the surface of the moon, showing that its surface is rugged 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 known as the moons of Galilee. He set out all his findings in his book “Sidereus Nuncius” (The starry messenger).
Galileo observed that Venus went through phases, just as the moon passes.
Composite image showing views of the spacecraft of Jupiter’s four largest moons. Known as satellites of Galilee, they were first seen by the Italian astronomer Galileo Galilei in 1610. They are shown from left to right in ascending order of Jupiter. Io is the closest, followed by Europa, Ganymede and Callisto. Image via NASA.
Galileo was a respected man in 1610, but his increasingly public acceptance of the heliocentric system began to cause him problems with the Roman Catholic Church.
In 1618, Galileo was dragged along by a controversy over the nature of comets, which did not help his social position. However, Galileo published the plot under his own name in “Il Saggitore” (The killer) in 1623, which is to this day one of his best known works.
Read the “The Killer” selections.
Things did not go much better for Galileo before his death in 1642. His work challenged the accepted Aristotelian view and earned him the wrath of the Roman Catholic Church, which had founded a group of institutions within the judicial system of the Church, known as the Inquisition, which aimed to combat heresy.
In particular, his 1632 publication of his “Dialogue on the Two Main World Systems, Copernican and Ptolemaic” was opposed to the Aristotelian view. In 1633, the Inquisition summoned Galileo to Rome. He was declared a suspect in heresy, was punished with life imprisonment and was formally abjured. However, he lived comfortably and was allowed to continue his work.
Galileo’s daughter, Sister Maria Celeste, was a nun in the Catholic Church. Letters were regularly written, and she kept the letters Galileo wrote to her, which were finally published in a book in 1999 by Dava Sobel called The Daughter of Galileo.
Despite Galileo’s battles with the church, he was a committed Catholic. He would probably like to know that the Vatican now has its own observatory and that some of its parents are astronomers. But it was not until 1992 that the Vatican admitted that Galileo was right in his heliocentric beliefs.
Galileo died on January 8, 1642.
The list of all Galileo’s discoveries is long. Although Galileo is highly praised for his various scientific discoveries, he did much more than promote science: he also promoted society. His life was much more than a mere 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 countless others to pursue the freedom of scientific research.
Portrait of Galileo by Justus Sustermans. Image via Wikimedia Commons.
Conclusion: One of our great astronomers, Galileo Galilei, was born on February 15, 1564. His discoveries with the improved telescopes he made have changed the way we see the universe.
