Galileo Galilei

Galileo Galilei was one of the first modern scientists, and made exciting discoveries about stars and planets using his telescope. He also found out about how things move as they fall to Earth. He was important because of the way he did his work. He observed carefully how things behaved and took notes. He then set up experiments to test his theories.

Galileo knew how to focus on what really mattered in a problem. And he did not just use words to describe how things move. He used mathematics. That meant he could say things very precisely.

Galileo was an important figure in the Scientific Revolution. This brought a new way of thinking to Europe in the 16th and 17th centuries.

GALILEO’S EARLY LIFE

Galileo was born near Pisa, in Italy, in 1564. He lived in Italy all his life. His father was a music teacher. When he was a child, Galileo studied in a monastery. He liked the quiet way of life there and wanted to become a monk. But his father sent him to the University of Pisa to study medicine. Galileo did not find medicine interesting and preferred mathematics. He eventually gave up his medical studies and taught mathematics instead. Soon, important mathematicians started to take notice of him. He became a professor of mathematics and taught at the universities of Pisa and Padua. His work made him famous. The powerful Grand Duke of Tuscany, Cosimo de’ Medici, made him his court mathematician.

GALILEO’S FIRST EXPERIMENTS

In Galileo’s time, people’s ideas about the world came mainly from the famous Greek philosopher Aristotle. Aristotle had said that heavy objects fall more quickly than light ones. Galileo found that Aristotle was wrong. He showed that if you drop a light object and a heavy object from the same height, they will speed up at the same rate and reach the ground at the same time. This was a surprise. It went against Aristotle’s ideas and common sense. But Galileo’s experiments showed that it was true.

Galileo also looked at pendulums. He found that they take the same time to complete a swing, however far they swing.

WHAT DID GALILEO DISCOVER?

In 1609, Galileo heard of an amazing Dutch spyglass that could make faraway things seem close at hand. He was fascinated. Soon he was making his own telescopes. They were much better than the early Dutch ones. Then one day he turned his telescope to the night sky. What he saw astonished him. Galileo found that the Moon had mountains, valleys and craters. He discovered that Jupiter had four little stars of its own going round it (he was seeing Jupiter’s four biggest moons). He found that the pale glow of the Milky Way was in fact the light of many thousands of faint stars. He watched sunspots. And he saw that the planet Venus showed phases, appearing as waxing and waning crescents just like the Moon.

These discoveries did not fit in with people’s ideas about the universe. Aristotle had taught that the heavenly bodies were smooth and perfect spheres. Yet the Moon clearly was not like that.

Aristotle and the Greek astronomer Ptolemy had believed the Sun and planets went round the Earth. In 1543 a book by Nicolaus Copernicus, a Polish astronomer, suggested that the Earth and planets went round the Sun instead. By Galileo’s time, many people thought it was true that the planets went round the Sun, but they still believed the Sun went round the Earth. Galileo could see that his work supported Copernicus. But Copernican theory went against the teaching of the Catholic Church. The Bible said that the Earth did not move, and was at the centre of the universe.

GALILEO AND THE CHURCH

In Galileo’s day, people could be tried and even killed as heretics if they wrote books that went against the Church’s teaching. The Inquisition was responsible for trying heretics. Galileo hoped he would be safe because the Pope liked his work. So he wrote a book showing that he believed that Copernican theory was probably true. But the book was banned and Galileo was tried by the Inquisition. He was forced to say he had been wrong, and was sentenced to life imprisonment, although he was allowed to live at home. He carried on working on moving objects, and wrote his most important book in these last years. Galileo died in Arcetri, near Florence, in 1642.


Galileo’s trial became famous. He had not wanted to go against the Church. He was a religious man. But he felt that people should accept what science had shown to be true when they interpreted the Bible. He thought you should not believe it blindly word for word.

Galileo only had simple telescopes. And not all of his arguments were correct. But now we have plenty of evidence that the Earth is just another planet going round the Sun. We have even found planets orbiting other stars.

Did you know?

• When Galileo left the University of Pisa in 1585 he did so without having passed his degree, although it had been medicine that he was studying and not the astronomy or physics that he would later be acclaimed for.
• In 1992 the Roman Catholic Church officially apologized for condemning Galileo to life imprisonment for going against their teachings in claiming that the Earth revolved around the Sun and not the other way round. After almost five centuries the Church had finally admitted that it was wrong and that Galileo was right.
• Legend has it that Galileo dropped two objects from the Leaning Tower of Pisa to show that if you drop a light object and a heavy object from the same height, they will speed up at the same rate and reach the ground at the same time. This story was first told by his last pupil and first biographer, Vincenzo Viviani, although many believe that at best it is more probably an exaggerated version of an actual event.