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Galileo Galilei

Galileo Galilei was a scientist from Italy. He made many important discoveries for astronomy. His accomplishments include his support for heliocentrism and his many improvements to the telescope.

 An illustration of Galileo on a stamp.

Personal Life

Galileo was born in Italy in 1564. His father was a famous musician and played the lute. Galileo had 5 siblings and his family often had money problems. 
Galileo had three children with a woman named Marina Gamba. He had two daughters, named Virginia and Livia, and a son named Vincenzo. Both of his daughters became nuns and his son was a musician like his grandfather. 

In 1633, Galileo was found guilty of heresy and sentenced to house arrest for the rest of his life! This was because he published a book supporting heliocentrism. This book criticised the Pope, who was the head of the Catholic Church. He was very powerful in Italy at the time. 

An image of a statue of the Pope.

The Catholic Church sentenced Galileo to house arrest for his support of heliocentrism.

Galileo died in 1642, at the age of 77. His family buried him in Florence, Italy, where there is a monument to him. An interesting fact is that one of Galileo’s fingers is on display at a museum in Florence! 

What did He Discover?

Galileo contributed to many scientific fields, including astronomy, engineering, mathematics, and physics. 


Today we know that in a solar system, the planets orbit around a star. That means that the star is the center of the solar system. In ours, for example, the Earth and all the other planets circle around the Sun. That’s what this idea is all about.

However, scientists didn’t always know this. Hundreds of years ago, people believed in a theory called geocentrism. This idea said that the Earth was the center of the universe. People thought that the Sun, the planets, and the Moon all went around the Earth.

This si what it would look like if the sun orbited the Earth.

People used to believe that the Sun circled the Earth. This was called geocentrism

In 1543 a scientist named Nicolaus Copernicus said that the geocentric theory was wrong. He argued that the Sun was the center of the solar system. Galileo agreed with this theory and worked to defend it. 
The Catholic Church, which was very powerful, fought against this theory. They said that the Bible supported the idea that the Earth was the center of the Universe. The Church felt that this new theory was a threat to their religion. Because of this, the Church had Galileo arrested for his claims! 


In 1608, Hans Lippershey, a lens maker, invented the first telescope. When he heard about this new instrument, Galileo built his own. He improved on Lippershey’s design for early telescopes and put his to use the following year.

Using his telescope, he discovered the four largest moons of Jupiter (now called Galilean Satellites) and the phases of Venus. He also found sunspots on the surface of the Sun and observed the physical features of the Moon! 

An image of an old brass telescope.

Galileo used early telescopes to discover new things about our Solar System.

Other Great Resources

More on Galileo’s Life:

Galileo’s Inventions:

Additional Facts about Galileo:

Written By: Leah Tolby