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Galileo and the Telescope: How 400 Years Ago Galileo Changed the World

Updated on January 24, 2010
Painted in 1636 by Justus Sustermans
Painted in 1636 by Justus Sustermans
Galileo's first 2 telescopes. Public Domain Image
Galileo's first 2 telescopes. Public Domain Image

Galileo Galilei

Galileo, an Italian professor of mathematics, did not invent the telescope. No one knows for sure who the first inventor was. But this new device spread quickly across Europe. At first it was more of a parlor toy and it was used by the military. But when Galileo heard of it, his first thought was it would be a great way to make some extra money! Teachers didn’t make much money in those days. He improved on the design and sold his telescope to merchants who used them to keep track of the ships coming into port. But because he was a man of ambition and imagination, he soon turned his telescope to the heavens in 1609 and astronomy was born. What he observed changed the course of the world.


Galileo’s Greatest Observations


Image credit: NASA/Apollo 12
Image credit: NASA/Apollo 12


Galileo first pointed his telescope at the moon and learned the moon was not smooth but covered by mountains and craters. This helped prove that the heavenly bodies were not perfect as touted by Aristotle and taught by the Catholic Church.


Composite by NASA.
Composite by NASA.

Jupiter and its Four Largest Moons

In January of 1610, Galileo discovered the four largest moons of Jupiter, now called the Galilean Moons, orbiting around Jupiter. It reinforced his view of a sun-centered universe introduced a century earlier by Polish Cleric, Nicolas Copernicus. Of course in the 1600’s the earth-centered universe proposed by Aristotle in the 14th century was the gospel truth and anyone disagreeing was in trouble with the Catholic Church.

Image to the right is the edge of Jupiter with its Great Red Spot, and Jupiter's four largest moons, known as the Galilean satellites. From top to bottom, the moons shown are Io, Europa, Ganymede and Callisto.

Venus in True Color

Image Credit:NASA/Image processed by R. Nunes
Image Credit:NASA/Image processed by R. Nunes

The Phases of Venus

In late 1610, Galileo observed the phases of Venus, which are very similar to the Moon’s phases.  He observed all of its phases and the only explanation could be it was orbiting the Sun, not the Earth. It was the first conclusive and observational proof of a sun-centered universe.


Other observations included:

the planets are disks, the sun has sunspots, the cloud called the Milky Way was composed of stars not seen before, Saturn had ‘ears’. His telescope was not good enough to see the whole rings so all he saw was pieces at either end that looked like ears.

Galileo’s Controversial Life

Galileo’s observations and publications, along with his unshakeable determination, threw him into disfavor with Pope Urban VIII. Eventually he denied what he knew to be true and stopped all of his astronomical investigations. He died under house arrest. A sad ending for a brilliant man, but his work lived on. Optics for telescopes was greatly improved showing more and more detail and seeing farther out into the universe. The Hubble Space Telescope has greatly expanded our knowledge of the universe and was the culmination of astronomers’ dreams to have a telescope in space.

2009 International Year of Astronomy

This year was dubbed The International Year of Astronomy. It is a celebration of the exploration of the universe and marks the 400th anniversary of Galileo’s first use of the telescope and recognizes his discoveries that created modern astronomy. Everyone is encouraged to get out and observe the heavens be it by the naked eye, binoculars or telescopes.



Astronomy Magazine Special Collector’s Edition

400 years ago – GALILEO


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    • Rose Kolowinski profile imageAUTHOR

      Rose Kolowinski 

      11 years ago

      Thanks Tony. Well, that's good. I didn't know that. I'm just glad there are people willing to stand up for what they believe. Thanks for reading and the comments. Peace to you too!

    • tonymac04 profile image

      Tony McGregor 

      11 years ago from South Africa

      Good Hub. Thanks for all the research and writing. The Church has belatedly apologise to Galileo - I suppose better late than never!

      Love and peace


    • Rose Kolowinski profile imageAUTHOR

      Rose Kolowinski 

      11 years ago

      Thanks, Lee. Hope you are doing well also. Thanks for stopping by and commenting.

    • Rose Kolowinski profile imageAUTHOR

      Rose Kolowinski 

      11 years ago

      He was a brilliant man ahead of his time. Thanks for your time and comments, Chad.

    • Chad A Taylor profile image

      Chad Taylor 

      11 years ago from Somewhere in Seattle...

      What a glimpse into this man's life as if you turned the telescope on history... Thank you!

    • Lee Thacker profile image

      Lee Thacker 

      11 years ago

      I like the way your brain thinks, makes me feel alive listening to what your thinking, very cool...Keep it up ...PS Now I Know Why I bookmarked your page ;-) ...Hope you are doing well,

    • Rose Kolowinski profile imageAUTHOR

      Rose Kolowinski 

      12 years ago

      Thank you Godslittlechild. I'm a big astronomy fan and I learned a lot too putting this hub together! Your time to read and comment is much appreciated.

    • Godslittlechild profile image


      12 years ago

      I enjoyed reading this hub very much! Learned a lot, Thanks!


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