Colby College Astronomy Blog: The Italian Genius

Galileo around 1610

Galileo Galilei (1564-1642) played a significant role in the scientific revolution that spread across Europe during the course of the sixteenth century. A native to Italy, he was not only an astronomer but also a philosopher, mathematician, physicist, and engineer. In 2016, he is known as “the father of the scientific method”, as well as titles that include the “father of observational astronomy and modern physics,” two distinct praises given to him by Albert Einstein.

Sidereus Nuncius

Perhaps what the Italian scientist was most controversial for during his lifetime, however, was his support for the beliefs of heliocentricism around 1610. It was in this year that Galileo published “Sidereus Nuncius” or Starry Messenger, a treatise which discussed new findings on the moons of Jupiter, the phases of Venus, and the discoveries of sunspots. It was also in this scientific pamphlet that he promoted the idea of Nicholaus Copernicus’s findings of a heliocentric theory. This idea is what we know today, in which the planets and Earth revolve around the sun at the center of our solar system. Back in the 1600s, however, most scientists believed in a geocentric model, which was the belief that the Earth is the center of the universe. While we know that this understanding is incorrect in 2016, during Galileo’s time, his discoveries were quickly met with opposition from not only astronomers but within the Catholic Church as well.

The belief in Geocentrism

Looking at it from the scientific standpoint, many of those who did not agree with Galileo’s findings based their beliefs on the lack of observed stellar parallax. Stellar parallax is the difference in direction of a celestial object, most often a star, as seen by an observer from two separate points on Earth - or from two separate points in the orbit of the Earth around the sun. If parallax could be observed, this would be evidence that the earth was not the center of the universe, since it was in motion around the sun. Because there did not appear to be any parallax, then this theory (meaning the heliocentric model) had to be incorrect.

The belief in Heliocentricism

There were also many in religion who did not believe in the theory of heliocentricism. In 1616, the Roman Catholic Inquisition declared that heliocentricism should be deemed heretical because it violated the Holy Scripture. In response, any heliocentric books, teachings, and so on were ultimately banned. Even Galileo was ordered by the Church to refrain from holding talks, conducting and teaching lectures, as well as defending any and all ideas that said Heliocentricism was correct.

But, how did Galileo come to support Copernicus’s idea of a heliocentric solar system to begin with? First, his discovery of the moons of Jupiter helped prove that not everything does revolve around the Earth after all. The second proof was based on the appearance of Venus in the sky. According to the geocentric model, Venus should always be visible to those on Earth, but go through phases just like the moon. If the Earth was the center of the universe, then Venus should always be the same distance from us; however, since Venus orbits the Sun, it appears farther away from us when it is on the other side of the Sun from Earth. Through his findings Venus’ appearance in the sky, Galileo was able to prove that Venus is actually orbiting the Sun.

Galileo being tried before the Inquisition

Yet another reason why Galileo staunchly believed in a geocentric theory was because he was able to show, using his telescope, that there was a whole universe out there of stars that were difficult for people to otherwise see with the naked eye. Knowing this, Galileo believed that the stars had to be much further away than was initially thought, especially those that are so dim that without a telescope, they cannot be seen. It was this idea, of far distant stars, that helped overcome the objection about a lack of stellar parallax. It is understandable that no parallax was observed, considering how distant the stars must have been from Earth.

After being cleared of all charges of heresy by the Catholic Church, Galileo did continue his studies in astronomy. As he did so, he continually became more and more convinced from his findings that the Earth did revolve around the Sun. Even though he was banned by the Church from ever teaching these ideas again, he ultimately set about publishing a second book that stated Copernicus’s theory of heliocentricism was correct. Once again, Galileo was called before the Inquisition to face charges. This time around, the famed Italian scientist was found guilty on charges of heresy, and in 1633, he was sentenced to life imprisonment. Fortunately, or unfortunately, Galileo was in his late seventies and suffered from poor health. Because of these factors, he was allowed to serve his punishment under house arrest instead, in his home in Tuscany. In 1642, he died while still under house arrest.

In history, Galileo’s controversial teachings became known as “The Galileo Affair.” Following the scientist’s death, it had been mostly forgotten until the Inquisition’s ban on reprinting Galileo’s works was lifted in 1718, less than one hundred years after his death. Although much of it had been censored, the general public was able to read the famous scientist’s works again. Over two hundred years later in 1939, Pope Pius XII described Galileo as being among the “most audacious heroes of research…not afraid of the stumbling blocks and the risks on the way, nor fearful of the funereal monuments” (Haitel, 7). In 1992, the current pope at the time, Pope John Paul II expressed his own regret as to how the Galileo situation was handled by the Vatican.

Sixteen years later, the head of the Pontifical Academy of Sciences, Nicola Cabibbo announced plans to erect a statue of Galileo inside the walls of the Vatican. Two months later, these plans were scratched, and as of today, there are no upcoming projects to honor Galileo by the Roman Catholic Church. In some ways, the Galileo Affair had been the first major confrontation between theology and science. Perhaps it would be an understatement to say that the Italian scientist’s teachings continue to live on.