who was the first to discover this system?
Galileo Galilei
Milky Way
Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. 
how many star are there in milky way galaxy It is estimated to contain 100–400 billion stars what is the milky way? It  is the galaxy that contains our Solar System, with the name describing the galaxy's appearance from Earth
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Milky Way [SEP] Introduction
The Milky Way is the galaxy that contains our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term "Milky Way" is a translation of the Latin ', from the Greek (', "milky circle"). From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe.