Refracting telescope
Refractors were the earliest type of optical telescope. The first practical refracting telescopes appeared in the Netherlands about 1608, and were credited to three individuals, Hans Lippershey and Zacharias Janssen, spectacle-makers in Middelburg, and Jacob Metius of Alkmaar. Galileo Galilei, happening to be in Venice in about the month of May 1609, heard of the invention and constructed a version of his own. Galileo then communicated the details of his invention to the public, and presented the instrument itself to the Doge Leonardo Donato, sitting in full council.
Visible-light astronomy
Hans Lippershey, a German-Dutch spectacle-maker, is commonly credited as being the first to invent the telescope. Lippershey is the first recorded person to apply for a patent for a telescope, however it is unclear if Lippershey was the first to build a telescope. Based only on uncertain descriptions of the telescope which Lippershey tried to obtain a patent for, Galileo made a telescope with about 3x magnification in the following year. Galileo later made improved versions with up to 30x magnification. With a Galilean telescope the observer could see magnified, upright images on the earth—it was what is commonly known as a terrestrial telescope or a spyglass. Galileo could also use it to observe the sky, and for a time was one of those who could construct telescopes good enough for that purpose. On 25 August 1609, Galileo demonstrated one of his early telescopes, with a magnification of up to 8 or 9, to Venetian lawmakers. Galileo's telescopes were also a profitable sideline; selling them to merchants who found them useful both at sea and as items of trade. He published his initial telescopic astronomical observations in March 1610 in a brief treatise entitled "Sidereus Nuncius" ("Starry Messenger").