To go from Saturn to Uranus in our model, we must walk as far as we’ve walked in our entire tour so far, again illustrating the vast distances that separate planets in the outer solar system. Uranus is much smaller than either Jupiter or Saturn, but it is still much larger than Earth. It is made largely of hydrogen, helium, and hydrogen compounds such as methane (CH4); the latter gives Uranus its pale blue-green color. Like the other giants of the outer solar system, it lacks a solid surface. At least 27 moons orbit Uranus, along with a set of rings similar to those of Saturn but much darker and more difficult to see.

The entire Uranus system–planet, rings, and moon orbits–is tipped on its side compared to the rest of the planets. This unusual orientation may be the result of a cataclysmic collision suffered by Uranus as it was forming some 4.6 billion years ago. It also is responsible for the most extreme pattern of seasons on any planet. If you lived on a platform floating in Uranus’s atmosphere near the north pole, you’d have continuous daylight for half of each orbit, or 42 years. Then, after a very gradual sunset, you’d be plunged into a 42-year-long night.

Uranus was the first “discovered” planet–all the planets closer to the Sun are easily visible to the naked eye and thus were known to all ancient cultures. English astronomer William Herschel discovered Uranus in 1781. He originally suggested naming the planet Georgium Sidus, Latin for “George’s star,” in honor of his patron, King George III. Fortunately, the idea of “Planet George” never caught on. Instead, many eighteenth- and nineteenth-century astronomers referred to the new planet as “Herschel.” The modern name Uranus, after the mythological father of Saturn, was first suggested by one of Herschel’s contemporaries, astronomer Johann Bode, and was generally accepted by the mid-nineteenth century.