Galileo was the first person to observe the rings of Saturn. He spent hour after hour on painstaking drawings of the Moon through its phases, observed Venus and Mars, and even made sketches of ...

Initially believing they were distant stars, Galileo’s repeated observations over several nights and realized they were moons orbiting the gas giant. And thus, Io, Europa and Ganymede became ...

Io, a highly volcanic world, is the innermost Galilean moon of Jupiter. Got a pair of binoculars? Point them at Jupiter tonight—or any night during its bright opposition month—and you’ll ...