was born on Feb 15, 1564 in Pisa, Italy. He died on January 8, 1642.
He is known to the entire world as ground-breaking astronomer, mathematician, physicist, inventor and philosopher.
Among his many inventions were telescopes, a thermometer and a compass.
Galileo enrolled himself in the University of Pisa to get a medical degree, but he never finished. He rather went on to choose to study mathematics.
He built on the work of others to create a telescope with about 3 times magnification.
He later improved on his own telescope and made it with around 30 times magnification. With these telescopes, Galileo was able to observe the sky in ways previously not achieved.
In 1610, he made observations of 4 objects surrounding Jupiter that behaved unlike stars, these turned out to be Jupiter's for largest satellite moons: Io, Callisto, Europa and Ganymede. They were later renamed the Galilean satellites in honour of Galileo himself.
The discovery of these moons was not supported by the scientific principles of the time and Galileo had trouble convincing some people that he had indeed discovered such objects. This was similar to other ideas put forward by Galileo that were very controversial at that time.
Galileo refused to believe in Kepler's theory that the moon caused the tides, instead believing it was due to the nature of the Earth's rotation. This particular incidence helps proving that even the smartest people can make mistakes.
The Geocentric model of the universe which was embraced by earlier astronomers had the Earth at the center of the universe with other objects moving around it. Work by Galileo, Nicolaus Copernicus and Johannes Kepler helped to supersede this theory with the more accurate heliocentric model. Such a view of the universe differed strongly with the beliefs of the Catholic Church at the time and Galileo was forced to withdraw many of his ideas and even spent the final years of his life under house arrest.
Famous Galileo quotes include: 'In questions of science the authority of a thousand is not worth the humble reasoning of a single individual.'
'Alas! Your dear friend and servant Galileo has been for the last month hopelessly blind; so that this heaven, this earth, this universe, which I by my marvelous discoveries and clear demonstrations had enlarged a hundred thousand times beyond the belief of the wise men of bygone ages, henceforward for me is shrunk into such a small space as is filled by my own bodily sensations.'
'See now the power of truth; the same experiment which at first glance seemed to show one thing, when more carefully examined, assures us of the contrary.'
Source: Sciencekid and wikipedia