Nearly 400 years ago, on January 7, 1610, Galileo Galilei turned his new telescope toward the planet Jupiter. In his notes and later in a publication titled Sidereus Nuncius, or The Sidereal Messenger, Galileo described his observations of Jupiter and its four moons, as well as his observations of our Moon and the planet Venus. A translation of this book was completed in 1800, and an online copy is available for your students to read courtesy of the Linda Hall Library (see Resources). This month’s Scope on the Skies column centers around Galileo and includes lessons based on his observations.