Tag Archives: Galileo

August 25, 1609 (a Tuesday)

Bell Tower in St. Mark’s Square

On this date, the Italian mathematician Galileo Galilei marched the Doge of Venice (Leonardo Donato), his counsellor, the Chiefs of the Council of Ten, and the Sages of the Order, who commanded the Venetian navy, up the Bell Tower (Campanile) in St. Mark’s Square in Venice, Italy. Once at the top, Galileo showed them views of distant cities, ships on the horizon, and parishioners entering a church on the island of Murano – all of which had been invisible to the eye alone – with the aid of his first telescope. The Doge was awestruck. The military had a powerful new secret weapon. Venice was confirmed again as a triumph. Galileo presented the Doge with the telescope on his knees and received a doubled salary, a lifetime appointment, and a bonus amounting to a year’s wages.

Throughout the the rest of 1609, particularly during the winter, Galileo made many astronomical studies. On January 7, 1610 Galileo observed with his telescope what he described at the time as “three fixed stars, totally invisible by their smallness,” all close to Jupiter, and lying on a straight line through it. Observations on subsequent nights showed that the positions of these “stars” relative to Jupiter were changing in a way that would have been inexplicable if they had really been fixed stars. On January 10 Galileo noted that one of them had disappeared, an observation which he attributed to its being hidden behind Jupiter. Within a few days he concluded that they were orbiting Jupiter. He had discovered three of Jupiter’s four largest satellites (moons): Io, Europa, and Callisto. He discovered the fourth, Ganymede, on January 13. Galileo named the four satellites he had discovered Medicean stars, in honor of his future patron, Cosimo II de’ Medici, Grand Duke of Tuscany, and Cosimo’s three brothers. [Later astronomers, however, renamed them the Galilean satellites in honor of Galileo himself.] On March 12, 1610 Galileo published the results of his studies in a brief treatise entitled Sidereus Nuncius (Starry Messenger).

These observations over a six night period, from January 7 through January 13, provided a view to Galileo that revealed that perhaps not everything orbited the Earth (geocentric model), as Ptolemy as well as the Catholic Church had adopted. And, if these small, but bright points of light went around Jupiter and not the Earth, perhaps there were other objects that did not orbit the Earth. His findings allowed him to confirm the Sun-centered theory of Copernicus. This short period of time from the summer of 1609 through to March of 1610, when Siderius Nuncius was published, had a revolutionary impact on astronomy almost overnight and it catapulted Galileo into the scientific spotlight and into the fire and wrath of the Catholic Church.

The Catholic Church condemned Galileo for his theories on June 22, 1633. He was forced to disown them and to live on his own for the rest of his life. In the following century the Vatican began changing its attitude. A mausoleum was built in 1734 to honor him. In 1822 Pope Pius VII gave permission for Galileo’s theory to be taught in schools. In 1968 Pope Paul VI had the trial against Galileo reassessed, then Pope John Paul II took the final step in the Church’s rehabilitation of the scientist in 1984 when he formally acknowledged that the Catholic Church had erred when it condemned the Italian astronomer for maintaining that Earth revolved around the Sun.

June 22, 1633 (a Wednesday)


On this date, the Florentine-Italian astronomer Galileo Galilei was compelled by the Roman Inquisition to recant the theory he held that  Earth travels around the sun.

March 31, 1596 (a Sunday)

René Descartes

On this date, the French mathematician, anatomist, physiologist, and philosopher René Descartes was born in La Haye in the region of Touraine, France. He is often regarded as the first modern thinker to provide a philosophical framework for the natural sciences as these began to develop. In his Discourse on the Method of Rightly Conducting One’s Reason and Of Seeking Truth in the Sciences (1637) he attempts to arrive at a fundamental set of principles that one can know as true without any doubt.

Descartes is also known for the mind/body dualism he first articulated in his De homine (Treatise on Man), which he completed in Holland about 1633, on the eve of the condemnation of Galileo. When his friend and frequent correspondent, Marin Mersenne, wrote to him of Galileo’s fate at the hands of the Inquisition, Descartes became concerned for his own safety and refused to have De homine printed. Consequently, the first edition of this work was not published until 12 years after the author’s death.

Figure 1 from Descartes’ De homine (1664), depicting the human heart.

According to Descartes’ principle of dualism, the body works like a machine, has the material properties of extension and motion, and follows the laws of physics. The mind (or soul), on the other hand, is described as a nonmaterial thinking entity that lacks extension and motion, and does not follow the laws of physics. Descartes argued that only humans have minds, and that the mind interacts with the body at the pineal gland. [He chose the pineal gland because it appeared to him to be the only organ in the brain that was not bilaterally duplicated and because he believed, erroneously, that it was uniquely human.] In De homine, he wrote:

I suppose the body to be nothing but a statue or machine made of earth, which God forms with the explicit intention of making it as much as possible like us…

William Harvey’s recent discovery that the heart acts as a pump to circulate the blood had supplied additional arguments in favor of Descartes’ mechanical theory – in fact, Descartes probably did much to popularize the discovery. The Cartesian dualism set the agenda for philosophical discussion of the mind/body problem for many years after Descartes’ death.

March 5, 1616 (a Saturday)

Cardinal Robert Bellarmine

On this date, the Copernican theory was declared “false and erroneous” by the Decree of the Holy Congregation of the Most Illustrious Lord Cardinals in charge of the Index (more commonly known as the Decree of the Index) written by Cardinal Robert Bellarmine, and issued by the Catholic Church in Rome. Further, no person was to be permitted to hold or teach the theory that the Earth revolves around the sun. When Galileo subsequently violated the decree, he was put on trial and held under house arrest for the final eight years of his life.

February 15, 1564 (Julian calendar/old style: a Tuesday)


On this date, the Florentine-Italian astronomer Galileo Galilei was born in Pisa, Italy. Galileo made a good discovery great. Upon hearing at age 40 that a Dutch optician had invented a glass that made distant objects appear larger, Galileo crafted his own telescope and turned it toward the sky. He quickly discovered that our Moon has craters, that Jupiter has its own moons, that the Sun has spots, and that Venus has phases like our Moon. Galileo, who lived to 1642, made many more discoveries. He claimed that his observations only made sense if all the planets revolved around the Sun, as championed by Aristarchus and Copernicus, and not around the Earth, as was commonly believed then. The powerful Roman Inquisition made Galileo publicly recant this conclusion, but today we know he was correct.

February 13, 1633 (a Sunday)

Galileo facing the Roman Inquisition.

On this date, Italian philosopher, astronomer and mathematician Galileo Galilei arrived in Rome to face charges of heresy for advocating Copernican theory, which holds that the Earth revolves around the Sun. Galileo officially faced the Roman Inquisition in April of that same year and agreed to plead guilty in exchange for a lighter sentence. Put under house arrest indefinitely by Pope Urban VIII, Galileo spent the rest of his days at his villa in Arcetri, near Florence, before dying on January 8, 1642.

Today, Galileo is recognized for making important contributions to the study of motion and astronomy. His work influenced later scientists such as the English mathematician and physicist Sir Isaac Newton, who developed the law of universal gravitation. In 1992, the Vatican formally acknowledged its mistake in condemning Galileo.

January 20, 1633


On this date, Galileo, at age 68, left his home in Florence, Italy to face the Inquisition in Rome. After two weeks quarantine (because of the plague) just outside Rome, he arrived there on 13 February.

By 22 June 1633, he had buckled under the threats and interrogation by the Inquisition, and renounced his “belief” that the Earth revolved around the Sun.

Aside from his theoretical works, Galileo made several contributions to “technology” such as an improved telescope, a thermometer, a military compass and many many others. So great was his legacy that he was called by Einstein the “father of modern science.”