ABSTRACT
On the night of 7 January 1610, from his university location in Padua, Galileo Galilei aimed his home-made telescope at Jupiter and observed three nearby brilliant stars on a line parallel to the ecliptic.1 The following nights, he was surprised to note that the three stars had swiftly changed their positions with respect to Jupiter and to one another: it became clear that they were not background stars, but natural satellites orbiting Jupiter. On 8 March, these findings had already been published in the Sidereus Nuncius, and provided empirical evidence that Copernicus was right.
