How did Galileo galilei?

A great Italian astronomer and physicist, renowned for his epoch-making contributions to physics, astronomy, and scientific philosophy. In 1610, he was among the first to use a telescope to study the heavens and with it discovered the four big moons of Jupiter, the phases of Venus, the mountains of the Moon, and the starry nature of the Milky Way, breakthroughs that he announced the same year in his Siderius Nuncius (Starry Messenger). His defense of the Sun-centered http://www.answers.com/topic/heliocentrism in Dialogue on the Two Chief World Systems (1632) brought severe censure from the Church and he was forced to recant before, at the age of 69, being sentenced to life imprisonment (commuted to house arrest); he was not formally exonerated by the Catholic Church until 1992. Having heard, in 1609, of the invention of the telescope, but lacking a detailed description, he set about learning the principles of the instrument himself and, within a matter of weeks, had produced his first simple "optik tube," which he immediately directed to the skies. Thus began a new and exciting era of observational astronomy that continues to this day. Galileo made a number of telescopes ranging up to 5 cm in aperture and 170 cm in focal length, and with magnifications from about 8 to 30.