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Ashley Richards
Physics 1040
April 21, 2013
Galileo Galilei
Galileo Galilei discoveries lead to significant contributions to the field of astronomy,
such as his extensive notes from his observations. Galileo’s contributions were so significant he
was also called the ‘father of modern observational astronomy.’ Although Galileo didn’t actually
discover Jupiter, he was the first astronomer to record extensive observations about the planet.
Further, he was also the fist astronomer to discover Jupiter’s four largest moons Lo, Europa,
Ganymede, and Callisto. Today these moons are also known as the ‘Galilean satellites’, in honor
of his discoveries.
Galileo began observing Jupiter in 1609. By 1610, he had documented that there were
“three fixed stars, totally invisible by their smallness” that were really close to Jupiter. He later
discovered that the ‘fixed stars’ had changed positions and were orbiting Jupiter. Interestingly
enough, Galileo attempted to estimate the periods of Jupiter’s moons with accurate estimations.
In September of 1610, Galileo also observed that Venus displayed a full set of phases
similar to the moons. By following the Copernicus heliocentric theory, his observations then
proved that the Sun was the center of the solar system. Galileo concluded that Venus was
orbiting the sun, not the Earth; passing behind the sun and beyond.
Galileo also observed Saturn in 1610. However, because of the crudeness of his
telescope, he was unable to determine what the rings were. He believed the rings to then be
moons on either side of Saturn. In 1612, Galileo had observed that the ‘moons’ had disappeared
due to his viewing the rings edge on. By 1614, he then observed that the ‘moons’ had returned
and that the rings were arms of some sort.
Although Neptune hadn’t been officially discovered until the 1800’s, Galileo had begun
documenting his observations of Neptune in 1613. There is new evidence that he may have
known the “star” had moved in relation to other stars. This is quite contrary to speculation that
Galileo had discounted the object as a star. In January 1613, Galileo wrote in his notebook that
the star-Neptune appeared to have moved relative to a nearby star and sketched a picture of what
he saw. In his drawing there is a mysterious unlabeled black dot, which is in the right position to
be Neptune.
Galileo discoveries have also impacted modern science. He studied mathematics and later
became professor and chair of mathematics at the University of Pisa. Until about 1609, he taught
mathematics, and made several discoveries in physics. He helped to mathematically describe
ballistics and the force of friction as it relates to motion. After experimenting with moving
objects, he established his "Principle of Inertia", which was similar to Newton's First Law.
Galileo then became interested in optics and astronomy. In 1609, he built his first
telescope and began making observations. The following year he published his first results,
where he described the highlands and "seas" of the Moon, four of Jupiter's largest moons, and
many newly discovered stars. He also discovered the phases of Venus and sunspots, thereby
confirming that the Sun rotates, and that the planets orbit around the Sun, not around the Earth.
But Galileo thought that most planetary orbits are circular in shape, when in fact they are
elliptical, as shown by Johannes Kepler. However, Galileo's observations have confirmed
Copernicus' model of a heliocentric Solar System. He challenged the basic principles of
Ptolemean cosmology, and put to rest Aristotle's theory that the heavens were "perfect and
unchanging", which was supported by the Catholic Church. But the Church still allowed Galileo
to conduct his research, as long as he did not promote the findings from his observations.
In 1632, the Pope was angry with Galileo when he published a book in which he openly
stated that the Earth was moving around the Sun. He was put on trial by the Inquisition in Rome,
where he was found suspect of heresy, and forced to say that all of his findings were wrong. He
was first imprisoned, and later confined to his house near Florence. Throughout the remaining
years of Galileo's life, the Church monitored his travel and communications with others, and his
writings were censored and placed in the Index of Prohibited Books. Galileo continued to write
about physics, and in 1632 he put forward his concept of Basic Relativity in physics, which may
be stated as follows: "the laws of mechanics will be the same for all observers moving at the
same speed and direction with respect to one another." (TC) This fundamental concept later
formed the basis for Einstein's Special Theory of Relativity.
Until the time of Galileo, European scientists relied heavily on Aristotle's approach of
philosophical analysis to explain physical phenomena. Galileo demonstrated the advantages of
experimentation, and argued that physics should be a mathematics-based science. “Galileo was
among the scientists, including Kepler, Newton and others, who began the Scientific Revolution
in Europe.” (RN) Galileo's work was instrumental in advancing the scientific method. His
experimentation and mathematical approach to physics was revolutionary.
Reflection: While reflecting on this semester, Elementary Astronomy has given me a new
perspective about Earth, our solar system, and the universe. Learning about old and modern
technology and theories, completing weekly current astronomy article summaries, to writing a
portion of a group project on Galileo Galilei, has further increased my interest in this subject.
Works Cited:
Chao, Tom. "The Most Famous Astronomers of All Time." Space.com. Space.com, 5 Feb. 2013. Web.
21 Apr. 2013.
Nirenberg, Ricards. "The Birth of Modern Science: Galileo and Descartes , a Lecture by Ricardo
Nirenberg. Fall 1996, the University at Albany, Project Renaissance." The Birth of Modern
Science: Galileo and Descartes , a Lecture by Ricardo Nirenberg. Fall 1996. University at
Abany, n.d. Web. 21 Apr. 2013.
Sobel, Dava. "Galileo's Place in Science." PBS. PBS, 29 Oct. 2002. Web. 21 Apr. 2013.
Van Helden, Albert, and Annulo Cinigiture. "The Galileo Project | Science | Saturn." Weblog post. The
Galileo Project | Science | Saturn. N.p., n.d. Web. 21 Apr. 2013.