Uranus - Known Facts

About Uranus, what scientific facts are known including trivia about the orbit, surface, and more.


Known Facts: In 1781 the British astronomer Sir William Herschel discovered the planet-the first of three to be found in the solar system in modern times. Herschel's discovery of Uranus lent credence to what is today known as Bode's Law. Actually neither a law nor devised by Bode, this curious arithmetical progression was advanced by the German astronomer J.D. Titius in the mid-1700s and provides the approximate distances of the planets from the sun in astronomical units (AUs). Because Uranus orbits the sun almost precisely at the distance beyond Saturn called for in Titius's progression, many astronomers began to search for other planets. This search culminated in the discovery of numerous asteroids, beginning with Ceres in 1801, and the eventual discovery of Neptune and Pluto.

Located near the periphery of the solar system, Uranus is one of the large, outer, or Jovian planets. Its distance from the sun varies from about 1,699 million mi. at perihelion to 1,867 million mi. at aphelion, the mean distance being 1,782 million mi., slightly more than double that of Saturn. Like its remote Jovian companions, Uranus has retained many of the gases out of which it was originally formed. Telescopic observations indicate that the planet's atmosphere consists largely of molecular hydrogen, helium, and methane. But unlike any other planet, the rotational axis of Uranus is tilted over so far that it lies almost in the plane of its orbit. This provides extraordinary seasons. Summer in Uranus's northern hemisphere finds the sun almost directly over the north pole, and much of the southern hemisphere in total darkness. Half a Uranian year later (42 Earth years), the situation is reversed, with the sun almost directly above the planet's south pole.

Five known natural satellites, or moons, orbit Uranus. They are Oberon and Titania (Herschel, 1787), Umbriel and Ariel (Lassell, 1851), and Miranda (Kuiper, 1948). More recently, astronomers have found Uranus to possess features strikingly similar to those of Saturn. An occultation of a star by Uranus occurred on Mar. 10, 1977, and led to the discovery of five thin rings of fragments encircling the planet in its equatorial plane. In 1978 three more rings were discovered. The rings, located inside the orbit of Uranus's nearest moon, Miranda, are at a distance of from 44,000 to 51,000 kilometers from the planet's center.

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