What did Galileo Galilei discover about astronomy?
Based only on uncertain descriptions of the telescope, invented in the Netherlands in 1608, Galileo, in that same year, made a telescope with about 3x magnification, and later made others with up to about 32x magnification. With this improved device he could see magnified, upright images on the earth – it was what is now known as a terrestrial telescope, or spyglass. He could also use it to observe the sky; for a time he was one of very few who could construct telescopes good enough for that purpose. On 25 August 1609, he demonstrated his first telescope to Venetian lawmakers. His work on the device made for a profitable sideline with merchants who found it useful for their shipping businesses and trading issues. He published his initial telescopic astronomical observations in March 1610 in a short treatise entitled Sidereus Nuncius (Starry Messenger). On January 7, 1610 Galileo observed with his telescope what he described at the time as “three fixed stars, totally invisible[26] by th