Portrait, attributed to Murillo, of Galileo looking at the words “It’s pure and moving” (“And yet it moves;” is not legible in this image) scratched on the wall of his prison cell. Image via Wikimedia Commons.
Happy birthday to the Italian astronomer, mathematician and physicist Galileo Galilei, born February 15, 1564. Galileo was one of the first to aim a telescope at the night sky, where he saw the phases of Venus and four points of light orbiting Jupiter ( now known as the famous Galilean months of Jupiter). These and other observations began to change the way we saw the universe and our place in it.
In the time of Galileo, educated people subscribed to the Aristotelian conception that the Earth is fixed in the center of a more or less unchanged universe. Therefore, his discovery of the moons orbiting Jupiter (now known as the Galilean satellites in his honor) and the phases of Venus resulting from the planet orbiting the sun were considered heresies by the Roman Inquisition. In 1633, these tribunals – which were developed by the Holy See of the Roman Catholic Church – forced Galileo to withdraw.
When he left the courtroom, he is said to have murmured:
It’s still moving (and still moving).
And so it happens. The earth moves and all objects in space move. The phrase is still used today as a reply, which means it doesn’t matter what you think; these are the facts.
Galileo spent the rest of his life under house arrest, but that didn’t stop him from publishing another paper, Two New Sciences, about mechanics and motion.
EarthSky’s monthly calendar shows the phase of the month for each day in 2021. Order before you leave!
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 to study medicine at the University of Pisa. Due to financial problems, he could not finish his studies, but his university years 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 it was to read the works of Aristotle. As Dante had said centuries ago, Aristotle is “the Master of those who know” (Dante, Hell 4,131). In other words, at that time, knowledge was for philosophy what faith was for religion.
And so, despite not being able to complete his medical degree and become a university professor, Galileo continued his studies in mathematics. He managed to get a few minor education jobs to earn a living. After two years of hard work, he published “La Bilancetta” (The little 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 see if his crown was made of pure gold or a mixture of metals of lesser value. Galileo presented an invention of its own, the “small equilibrium”, now called “hydrostatic equilibrium”, which is used to make more accurate measurements of density differences.
Read here about the king’s crown and about Archimedes’ other discoveries.
Galileo’s reputation was shattered after the publication of “Du Motu” (On the move), a study of falling objects, which showed his disagreement with the Aristotelian view of the subject.
In 1609, he heard that an instrument had been invented in the Netherlands that showed distant objects as if they were nearby. Like many others, Galileo quickly realized the mechanics of the telescope, but later greatly improved the original design. He presented the Venetian state with an eight-motor telescope, a telescope that magnifies normal vision eight times. His telescope brought him a double salary and a lifetime term at the University of Padua.
Over the years, Galileo has improved its telescope to magnify up to 20 times.
One of Galileo’s telescopes. Image via the 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 surface of the moon, showing that its surface is rugged and rocky, contrary to popular belief that the moon was smooth.
In January 1610, he discovered the four largest months of Jupiter: Io, Europa, Ganymede and Callisto. Today, they are called the Galilean months. He presented all his discoveries in his book “Sidereus Nuncius” (The starry messenger).
Galileo noticed that Venus went through phases, just like the moon.
Composite image showing the starships of Jupiter’s largest four-month spacecraft. Known as Galilean satellites, they were first seen by Italian astronomer Galileo Galilei in 1610. Displayed from left to right in order of increasing distance from Jupiter. Io is the closest, followed by Europe, Ganymede and Callisto. Image via NASA.
Galileo was a respected man until 1610, but his growing public acceptance of the heliocentric system began to cause him problems with the Roman Catholic Church.
In 1618, Galileo was dragged into a controversy over the nature of comets, which was of no help to his social position. However, Galileo published the argument under his own name in “Il Saggitore” (analyzer) in 1623, which is to date one of his best known works.
Read the selections from “The Assayer”.
Things did not go much better for Galileo before his death in 1642. His work continued to defy the Aristotelian accepted point of view and brought him the wrath of the Roman Catholic Church, which had founded a group of institutions in the Church’s judicial system – known as the name of the Inquisition – whose purpose was to combat heresy.
In particular, his 1632 publication of the “Dialogue on the Two Main World Systems, Copernican and Ptolemaic” opposed the Aristotelian view. In 1633, the Inquisition summoned Galileo to Rome. He was declared a suspect in heresy, sentenced to life imprisonment and was forced to formally abjure. However, 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 saved the letters Galileo wrote to her, which were finally published in a book in 1999 by Dava Sobel called Daughter of Galileo.
Despite Galileo’s struggles with the church, he was an employed Catholic. He would probably be delighted to learn that the Vatican now has its own observatory and that some of his parents are astronomers. But it was not until 1992 that the Vatican recognized 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 did much more than push science forward: he pushed society forward as well. His life was much more than 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 release the science of philosophy. He inspired countless others to pursue the freedom of scientific inquiry.
The Portrait of Galileo by Justus Sustermans. Image via Wikimedia Commons.
Conclusion: 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 look at the universe.
