On January 7, 1610, Italian astronomer Galileo Galilei turned his newly developed telescope to Jupiter. 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 (who ruled Italy at the time), and gave them numbers. German astronomer Simon Marius also claimed to have seen these objects at about the same time. He never published any documentation, and the credit was given to Galileo. It was nearly 250 years later before they were given names. They are now known as the Galilean moons, Io, Europa, Ganymede and Callisto. They were created at the same time as Jupiter and contain 99.999 percent of all the mass in orbit around Jupiter. How much do you know about these moons? What would Ganymede be called if it did not orbit Jupiter? What is the most volcanic place in our solar system? Why does Europa have spots? Which moon is a good candidate for containing life? Find out the answers to these questions and more and amaze your family and friends with these fun facts. Ages 8 and up. All measurements in American and metric. Educational Versions include exercises designed to meet Common Core standards. LearningIsland.com believes in the value of children practicing reading for 15 minutes every day. Our 15-Minute Books give children lots of fun, exciting choices to read, from classic stories, to mysteries, to books of knowledge. Many books are appropriate for hi-lo readers. Open the world of reading to a child by having them read for 15 minutes a day.