Galileo is often called the founder of modern science. He made many discoveries in astronomy and physics and he built telescopes to study space.
Galileo Galilei was born in Pisa, Italy in 1564. His father sent him to the university to study medicine, but young Galileo was more interested in science and mathematics.
Galileo made one of his greatest discoveries as he sat in a cathedral of Pisa. As he watched a chandelier swing back and forth he noticed that longer and shorter swings took the same time. This discovery became known as the law of the pendulum. These and other important discoveries made him so well-known that Galileo became a professor at the University of Pisa.
Galileo often questioned scientific facts of his age. For a long time people thought that heavier objects fall to Earth faster than lighter ones. By dropping objects of the same size but different weights from the Leaning Tower of Pisa Galileo showed that this wasn't true.
In 1609 Galileo constructed his first telescope. He used it to observe the stars and the planets. He saw things that nobody had ever seen before. Galileo discovered that the moon's surface was not smooth and flat, like everyone thought, but had a rough surface and was full of craters.
In January 1610 Galileo discovered 4 moons revolving around the Jupiter. They were named after him, the Galilean moons. These observations proved that not the Earth was the centre of the solar system, but the sun. It was a discovery that Copernicus had made 60 years earlier.
The Roman Catholic Church did not always like what Galileo taught. It still believed that the Earth was the centre of the universe and everything revolved around it. The church ordered him not to teach such ideas any more.
In 1633 Galileo was brought before the Inquisition, the Church's court. It sentenced him to life in prison because of his teachings. Galileo was put under house arrest because he was old and not so healthy any more. He spent the last years of his life in Florence, where he continued to work on his theories and even published a final book. He became blind and died in 1642.
In 1992 Pope John Paul II published a document that said the Church made a mistake by condemning Galileo.