The year 2009 is being observed as the “International Year of Astronomy” throughout the world. It is the 400th year of observation of sky through a telescope by the great Italian scientist and astronomer Galileo. Galileo turned his telescope for the first time in 1609 towards the sky and discovered many celestial objects. This marked a significant change in the progress of astronomy and astrophysics.

In fact, as many believed, Galileo is not the inventor of telescope. The first telescope was constructed by Dutch glass-maker Hans Lippershey in 1608 by using a combination of a convex and concave lens.  Lippershey  never used his telescope for astronomy. It was mainly used for spying and warfare activities. Galileo was in Venice, when in 1609, he received the news of the invention and description of telescope from his friend Polo Sharpy. Galileo built his own telescope in July 1609. Its magnifying power was 3. In August 1609, he built a telescope with magnifying power of  8 and presented it to the Senate of Venice. In November 1609 he built a large telescope with magnifying power of 20 and used it for observation of celestial bodies. In fact, the name ‘telescope’ was used for the first time by Prince Frederick Sesi in 1611 during a demonstration of the telescope by Galileo in Venice.

The popularity and demand of telescope was increased day by day. Galileo established a factory to manufacture telescope. He produced more than hundred telescopes there and presented to his friends and to some royal families. Queen of France, King of Rome, Prince of German, King of Italy and many priests had requested Galileo for telescope. He also sold telescopes in France, Holland, Germany and others European countries.

Galileo is called the father of modern science. He is famous for his discovery of law of falling body, inclined plane, acceleration, projectiles, pendulum etc. He was the first scientist to demonstrate science with experiments. By experiments he had proved many Aristotelian believes to be wrong. By his famous ‘Pisa Leaning Tower’ experiment he proved that bodies of different weights fall from a height on the ground at the same time.

Galileo was born at Pisa in Italy on February 15, 1564. After studying at Pisa University he worked as professor, first at Pisa University and then at Padua University. He worked in the field of physics, engineering, mathematics and astronomy. He supported the heliocentric theory of Copernicus. This theory tells that the Earth moves around the Sun which went against the Aristotelian view of geo-centric theory. At that time Church was powerful. Church believed the geo-centric theory and any body opposing it was considered as heretic. As a result Galileo became the target of the Church. He was put behind bar and the last part of his life was spent under house arrest.

We shall see the achievements of Galileo in astronomy. Till that time astronomers were observing the sky with naked eye and so they were unable to locate distant objects and observe the details of celestial bodies. Galileo, with the help of his powerful telescope, brought a revolution in astronomy. In December 1609, he made four significant observations. These are mountains and craters on the Moon, four satellites of Jupiter, phase of Venus and individual stars in the Milky Way galaxy. The first of these observations revealed that the surface of the Moon is not at all smooth as it appears to be.  From the shadows of the mountains he could measure their heights.

His discovery of first four satellites of Jupiter in 1610 is an important milestone in the history of astronomy. The satellites named Ganymede, Callisto, Io and Europa are now known as the Galilean satellites after this name. This discovery proved wrong the idea that all celestial bodies revolves around the Earth. This and the discovery of the phases of Venus were also used as evidences in favour of heliocentric model of Copernicus. His observation of stars in the Milky Way showed that the Milky Way is composed of many stars.

Galileo published all his celestial observations in a book Sidereus Nuncius (The Starry Messenger) in March 1610. Galileo discovered sun spots with his powerful telescope in 1611. On turning his telescope towards Saturn, he saw it in three parts. After two years, he could clearly see the rings of Saturn. He has founded the telescope astronomy and within the last 400 years it has developed enormously.

Galileo died on January 8, 1642 at Florence in Italy. At that time he was complete blind and was under house arrest in his own home by Pope. After his death it was planned to organize a condolence meeting and to build a memorial at his burial place. The Pope warned the King of Tuskani (Florence belongs to Tuskani) against this. At last Galileo was buried in an unknown place.

No body else has suffered like Galileo for propagating the truth of science.