From earliest times, humans have wondered about the sky above them. Simple telescopes in the 1600s made possible descriptions of the wonders of Earth's Moon and the closer planets. It took the development of powerful telescopes and modern space probes to learn more about the more distant planets—Jupiter, Saturn, Uranus, and Neptune. In this book, we'll explore seven wonders of these four enormous planets—called the gas giants—and their moons. On Saturn, we'll examine its amazing rings and their properties. On Jupiter, we'll investigate the Great Red Spot—a gigantic storm about twice the size of Earth that has lasted for centuries. We'll also explore a moon of Jupiter with erupting volcanoes, a moon of Uranus covered with one of the weirdest landscapes in the solar system, a huge crater on a tiny moon of Saturn, as well as planet auroras much more spectacular than Earth's northern lights. We'll also consider how the discovery of water on Jupiter's moon Europa may mean that life is possible in other worlds.