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It was in 1609 that Galileo became aware of a Flemish instrument made of two lenses fitted into a cardboard tube. Galileo improved this instrument by using well-polished lenses, and eventually obtained a magnifying power of approximately thirty times.
In the Starry Messenger, Galileo reported the discoveries made with the telescope between 1609-1610:
1: visible stars were only a small part of the existing ones.
2: the Moon was not a perfect spherical body, but was similar to the Earth.
3: there were four faint stars revolving around Jupiter. Galileo christened them "Medicean stars", in honour of the Grand Duke of Tuscany.
In 1610-1611, Galileo made other discoveries.
4: also the Sun was not a perfect spherical body, its surface being locally obscured by spots.
5: Saturn had a tripartite planetary body, having two strange lobes on the opposite sides of the central spherical part.
6: Like the Moon, Venus also showed a complete series of phases.
Galileo introduced the telescope and his discoveries to the Venetian Senate, the Medici's Court, and the Jesuit fathers of the Roman College. These discoveries seemed barely credible, and Galileo often had to persuade sceptics that the telescope's lenses did not produce hallucinations.
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Telescope