Galileo Galilei was born on February 15, 1564 in Pisa, Italy to Vincenzo Galilei and Giulia degli
Ammannati. He was the eldest of six children and belonged to a noble family. ("The Galileo project," n.d.)
Although they were noble, they were by no mean rich. Galileo’s father worked as a musician and even
though it didn’t make their family wealthy, it made them enough to send their first born to college at the
University of Pisa. Throughout his life, and especially through his early years of schooling, Galileo’s father
made an effort to “[direct] his son away from the pure mathematical formulas followed at the time, toward
experimentation and observation, with results explained by empiricist mathematics.” (Whitehouse, 2009)
It is through this experimentation and observation that Galileo made so many contributions to the world’s
understanding of physics and astronomy. There are three contributions in particular that this paper will
focus on: first, his experimentation with inclined planes and how this increased man’s understanding of
motion and inertia; second, Galileo’s utilization and popularization of the telescope and how that changed
man’s view of the heavens; and third, Galileo’s study of the planets and how that led to a broader
understanding of the universe. As Galileo grew older and as he attended college at the University of Pisa,
it was his father’s intention that he study medicine. But as Galileo grew fonder of mathematics, he changed
his profession to mathematics and philosophy. After several years of schooling and no degree, Galileo
ended up obtaining several lecture and research positions, at several universities, throughout his life. It is
during these tenures, between the 1580’s and the 1630’s, that we see most of Galileo’s scientific
contributions. ("The Galileo project," n.d.) One of those contributions was his work in motion and inertia.
Prior to Galileo’s work in motion, Aristotle had, through observation, proposed that two distinct
types of motion existed on the earth: natural motion, which describes vertical motion of objects, and
violent motion, which describes any kind of horizontal motion of an object. He also proposed a third
kind of motion called Celestial motion, which only applied to the heavenly bodies, which described their
motion as circular. Aristotle also professed that an object needs a push or a pull in order for it to keep
moving. It was from this hypothesis that Galileo began his work, by stating the opposite; that if no force
acts upon an object, it will continue in its current motion, there is no push or pull necessary to sustain that
motion. (Hewitt, 2006) Galileo worked on proving his hypothesis by working with inclined planes. He
began by rolling a ball down an angled plane. He observed that as the ball rolled down the incline its speed
increased, and as he rolled it up the incline its speed decreased. From these experiments he reasoned that
if rolled on a horizontal plane, the ball would neither speed up nor slow down, it would simply come to
rest “not because of its “nature” but because of friction.” (Hewitt, 2006) He studied further the nature of
friction and found that the smoother the surface on which the balls were rolled, the less friction there was
and the longer the balls rolled before stopping. From this experiment he concluded that in the absence of
friction or any other opposing force, an object moving horizontally would continue to move in that
direction indefinitely. (Hewitt, 2006) This concept is commonly known as inertia; the property of things
to resist changes in motion. Galileo’s work in motion and inertia opened the door for Sir Isaac Newton
and his work, contributing greatly to his first law, the law of inertia.
Another contribution made in one of his various terms as a professor, was the significance of his
decision to start using a telescope. Although Galileo himself did not invent the object known as a
telescope, he did recreate and utilize it to its full potential. (Maran & Marschall, 2009) In 1609, Galileo
heard about an instrument in the Netherlands that enabled you to see thing that were far away as if they
were close. Interested by this object, Galileo sought to make his own. After he learned how to
manufacture the object, he worked on improving its design and magnification power. He “taught himself
the art of lens grinding, and produced increasingly powerful telescopes….” ("Galileo," n.d.), and turned a
three-power telescope into an eight-power one. He worked quickly to try and gain recognition for his
highly magnified scopes because there were others working to capitalize on the concept. He presented his
improved version to a group of Venetian gentlemen who were greatly impressed; so impressed in fact, that
they convinced the Venetian Senate to grant him professorship for life and to double his salary at the
University of Padua. (Whitehouse, 2009) Even though his initial reaction to the telescope was one of
admiring its practicality in military use and most of his early experimentation with this new device
remained strictly terrestrial, he did eventually look heavenward. But it wasn’t until December of that year,
1609, that he even considered using it for astronomical purposes. (“The Galileo project, n.d.) There was
no turning back once he saw what he did that night and it was because of his improvements and
application of this new instrument that made those planetary observations possible. Sure, man might have
eventually discovered its application in observing celestial bodies, but it was because of Galileo’s incredible
ability to manufacture telescopes with increased magnification and his intense curiosity that the heavens
opened up as quickly as they did. It is believed that the moon was his first subject for observation and what
he saw amazed him.
Up until that December night, the world had believed that the moon’s surface was smooth and
uniform, but Galileo’s observations proved otherwise. There were many other assumptions about the
universe that had remained unobserved for centuries that were now open to speculation in 1610, all
because of this new instrument of scientific evaluation. Within the course of 2 years, Galileo managed to:
map out star formations, write extensively on sun spots, discover the four satellites of Jupiter, publish his
observations about Jupiter and its moons, and discover Saturn’s rings and phases, which verified the
Copernican system. (“The Galileo project”, n.d.) Galileo’s published works about the planets and their
movement brought him great fame, but it also got the attention of the Catholic Church. Galileo’s writings
in his book Dialogue Concerning the Two Chief World Systems compare the widely accepted Ptolemaic
system, the Sun and other planets revolve around the Earth, with the Copernican system, Earth and other
planets revolve around the Sun. It is important to note that prior to Galileo’s publication, the Copernican
system had already been admonished by the Church. Knowing this, Galileo was very careful about what he
published, especially after a previous run in with the Church. So he made great efforts to make sure that
this new book had their approval before he proceeded to print and distribute it. Unfortunately, due to
some miscommunication, Galileo inadvertently had his book Dialogue published without the Church’s
consent, all the while believing he had been given permission. This landed him in a great deal of trouble
with the Pope and the Roman Inquisition. (Whitehouse, 2009) The end result of this inquisition was
Galileo being sentenced to house arrest for the remainder of his life. Although this is a tragic end to his
amazing life, the world was blessed by the publication of his discoveries. One author writes that, “Albert
Einstein regarded the scientific reasoning by Galileo as one of the most important achievements in the
history of human thought. Galileo’s work marks the real beginning of physics and his legacy is still with us
today.” (Whitehouse, 2009)
Galileo Galilei contributed immensely to not just to the study of physics, but to the study of
astronomy as well. His work in motion and inertia laid the groundwork for future generations, like Isaac
Newton, to expound on his theories, producing more solidified theories and laws that govern our modern
day physics. His work on the increasingly popular telescope helped to expand man’s view of the heavens.
By popularizing the notion of increased magnification of the telescope’s lens, Galileo, again, laid the
groundwork for future scientists who to this day are continually working to improve their view of the
heavens. Galileo’s studies and observations about our solar system and its workings may have caused his
life to end in tragedy, but our modern world would be nowhere near where it is today without them. His
works inspired thousands of young scientists in the generations that followed, sparking a revolutionary
trend in observation and experimentation that would lead to changes in the way we view and understand
our planet, our solar system and our universe.