Galileo Galilei

by Patricia from Spokane

“The Bible shows the way to go to heaven, not the way the heavens go”

Galileo Galilei (
Galileo Galilei (

Galileo Galilei, born February 15, 1564, was one of the most important figures in the Scientific Revolution. He lived in Italy in a period when religious leaders were also powerful political leaders who could enforce the teachings of the church with imprisonment, torture or death by the Inquisition. Despite this culture, Galileo studied Mathematics and Philosophy and became a brilliant creative thinker. He discovered several basic laws of motion and studied the night sky. Galileo read “On the Revolutions of the Heavenly Spheres” by Nicolaus Copernicus, in which Copernicus proposed that the Earth was not stationary with the Sun, planets, and stars orbiting it, as everyone believed, but that Earth actually rotated and orbited around the Sun. Galileo saw merit in this theory despite that fact the Church did not.

Galileo's telescope (
Galileo's telescope (

In early 1609, Galileo heard that a Dutch eyeglass maker had put a convex lens and a concave lens, each of just the right strength, together and created a device that could magnify things. Galileo immediately imagined the potential of such a device and set about to improve it. He learned to grind lenses and used his knowledge of optics to create the first telescope. The telescope allowed him to see objects in the night sky with a whole new level of clarity. He made very detailed drawings of the craters, mountains, and other imperfections of the moon. In 1610 he observed four very small points of light in a perfect line near Jupiter and viewed them several nights and discovered that they were moons of Jupiter. The fact that the moons orbit Jupiter and not the Earth convinced him that Copernicus’s heliocentric theory was right; now he needed an experiment to prove it. Galileo’s protégé, Benedetto Castelli suggested that if all of the planets, including Venus, circled the Sun, then Venus should sometimes appear to have a crescent shape or sometimes not, similar to the phases of the moon. Upon examination with his telescope, Galileo confirmed that Venus had phases, and therefore confirmed that it orbited the Sun.

Jupiter's moons (<br>planets/profile.cfm?Display=Moons&Object=Jupiter)
Jupiter's moons (

In 1616 the church warned Galileo not to publish any more papers in support of the heliocentric theory because it was contrary to a literal interpretation of several passages in the Bible. Galileo agreed to this, however, he finally stood up for what he knew to be the truth. He tried to convince important leaders, including the Pope himself, that the Bible was a book explaining the path to salvation, not an astronomy text, and that the evidence for the heliocentric system was too solid to deny it. Galileo was given permission by the Pope, one of Galileo's biggest supporters, to publish his findings, as long as the heliocentric theory was only portrayed as an unconfirmed hypothesis and that the Church’s traditional views were also to be expressed, as well as the Pope's own views. In 1630 Galileo finished “A Dialogue Concerning Two Chief World Systems” which structurally followed the Pope’s instructions. Unfortunately, it was found to have a strong bias in favor of heliocentricity and the invented character arguing for the church’s Earth-centered model of the universe, Simplicius, was a simpleton. Also, unfortunately, the views of Pope Urban VIII were inserted into this uncomplimentary spokesman. The Roman Inquisition tried Galileo for heresy, forced him to denounce the heliocentric theory, and sentenced him to house arrest for the rest of his life. Despite this, Galileo continued to write about mathematics and the physics that would, after his death, influence Sir Isaac Newton and even Albert Einstein.

In addition to being a great scientist, Galileo was also a model for the ethical value of citizenship. Sometimes being a good citizen means following the dictates of authority, but sometimes it means standing up for what is right, even if the people in power disagree with you. Galileo’s fight for the truth and for valuing reason and logic led to him being a pioneer of the "experimental scientific method" and eventually helped us to have a better understanding of the universe we live in.

Page created on 4/21/2014 10:02:52 PM

Last edited 10/17/2019 8:15:40 PM

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Related Links

Galileo's Battle for the Heavens - timelines, video, and more information about Galileo's experiments
The Galileo Project - information on his life and his family
Telescopes from the Ground Up - Explore the history of telescopes, from Galileo to NASA's Great Observatories.
Read "Galileo," a play by Brecht, Bertolt (1898-1956) on Internet Archive - The Internet Archive, a 501(c)(3) non-profit, is building a digital library of Internet sites and other cultural artifacts in digital form. Like a paper library, Internet Archive provide free access to researchers, historians, scholars, the print disabled, and the general public. Internet Archive's mission is to provide Universal Access to All Knowledge.

Extra Info

The name of this great scientist lives on. In 1995 an important NASA research mission was named after Galileo. "The Galileo Mission" involved two spacecraft: an orbiter and an atmospheric probe that were kicked out of Earth's orbit by an inertial upper stage (IUS) rocket, sending them careening through the inner solar system. The trajectory which the spacecraft followed was called a VEEGA (Venus-Earth-Earth Gravity Assist), traveling first in toward the Sun for a gravity assist from Venus before encountering the Earth two times (spaced two years apart). These encounters with Venus and the Earth allowed Galileo to gain enough velocity to get out to Jupiter.

Galileo Jupiter flyby (Sky & Telescope)

During the flybys of Venus and the Earth, Galileo's scientists took the opportunity to study these two planets as well as the Moon, making some unprecedented observations. In addition, following each Earth flyby, Galileo made excursions as far out in the solar system as the asteroid belt, enabling scientists to make the first close-up studies of two asteroids, Gaspra and Ida. The Galileo mission scientists were fortunate to be the only ones with a direct view of the Comet Shoemaker-Levy 9 fragment impacting on Jupiter.

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MY HERO celebrates the International Year of Astronomy 2009

400 years of telescopes being used for outreach...

25 August is an important day for IYA2009 as 400 years ago Galileo conducted the first astronomical outreach activity when he met with policy and law-makers from the Venetian Republic. He ushered them into the bell tower of St. Mark's Square, and then presented them with a telescope design which he himself had improved. Impressed with seeing objects such as ships from a great distance, they saw great potential in continuing work on this eight-powered telescope, and improving the design further. Galileo's salary was doubled and he was awarded life tenure at the University of Padua, an excellent reward.

This first outreach activity with a telescope was a resounding success for Galileo. He used his novel telescope to communicate with policy-makers and the public, and as a result obtained funding for continuing his research, and presented people with a tool to expand their horizons.

Telescopes are invaluable instruments to both amateur and professional astronomers. Collecting more light than the unaided eye is able, they allow us to peer into the depths of space and witness sights previously beyond our realm. They are also iconic, instantly recognizable even to someone with no knowledge of astronomy. Telescopes conjure images and emotions of exploration and investigation, which is at the heart of IYA2009.

When Galileo first turned his telescope to the skies, he was awestruck by what he saw. This same feeling is being imparted to millions of people during IYA2009, as telescope observing sessions are being run around the world, allowing all members of the public, many for the first time, to view the Universe in all its glory.

The 365 Days of Astronomy project has released a podcast marking this occasion: Galileo presents a telescope to the Venetian Senate