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 ...

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 ...

The four biggest moons of Jupiter aren't just blurry smudges in Galileo's telescope anymore. The Italian astronomer Galileo Galilei discovered Ganymede, Callisto, Europa and Io back in 1610 ...