One of the most significant discoveries of Galileo Galilei was the existence of the system of moons orbiting the planet Jupiter.  He made this discovery through a telescope he fabricated in his own workshop.  He first observed the system on January 7, 1610.  It is a tribute to his keen sense of observation that he deduced the true nature of the system.  By careful observation he determined the "stars" that were moving in such a strange manner were indeed not stars at all but were small celestial bodies moving around the planet Jupiter.  His discovery supported the Copernican theory of a Sun centered "universe".  His controversial discovery and his support of Copernicus's views led to his imprisonment by the "Inquisition".

Click here to view an image with the Galilean moons identified. For a high resolution grayscale image of Jupiter's Galilean system, click here.