He discovered four objects orbiting the giant planet. It took him another night’s observations to clearly distinguish between two of them.
He called them ‘The Medicean Planets’ after the Medici family and gave them numbers.
Having previously been encouraged in his other scientific studies by the Church in Rome Galileo made his findings known to the Pope. Much of his disappointments, the Church soon took exception to his assertions that Earth was not the center of the universe and forbade his to continue his research or to even discuss it openly.
It was nearly 250 years later before they were given names: Io, Europa, Ganymede and Callisto. Galileo initially named his discovery the Cosmica Sidera but names that eventually were chooses by Simon Marius.
Galileo’s discovery proved the importance of the telescope as a tool for astronomers by showing that there were objects in space to be discovered that until then had remained unseen by the naked eye.
Discovery of Galilean Moons by Galileo Galilei