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Uranus is a bluish “ice giant” planet with a diameter equivalent to four Earths and a mass slightly greater than 14.5 Earths. It has a unique axial tilt of 97.77° and is the coldest planet in the solar system. It has small rings and 27 known moons, with Miranda being the largest. Uranus was discovered in 1781 by Sir William Herschel and has a mostly hydrogen atmosphere with small amounts of methane ice that give it its aquamarine color.
Uranus is a large bluish planet that orbits about 19 AU (Earth-Sun distances) from the Sun. With a diameter equivalent to four Earths and a mass slightly greater than 14.5 Earths, Uranus is the third largest planet in the solar system, after Jupiter and Saturn. Although composed primarily of hydrogen gas, Uranus and its sister planet Neptune are often referred to as “ice giants” rather than “gas giants” due to their different composition from the latter. Uranus’ aquamarine color comes from small amounts of methane ice suspended in its mostly hydrogen atmosphere.
Although Uranus can be seen with the naked eye and has been observed since prehistoric times, people always mistake it for a star. For this reason Uranus was not discovered to be a planet until Sir William Herschel observed it on March 13, 1781. Unfortunately, he initially thought it was a comet. When he sent his observations to other astronomers so they could take a look at it, many suspected it was actually a planet. After a couple of years its planet was universally recognized and the name Uranus caught on, even if it was initially called “Star of George” in honor of King George III.
Uranus revolves around the Sun approximately every 84 Earth years, orbiting at a distance of approximately 3 billion km. Uranus is unique in being a strangely cold planet: although Neptune generates about 2.4 more heat than it receives from the Sun, Uranus barely generates any heat. The reasons are not fully known. The 49 K temperature of some of its cloud features is the lowest temperature measured in the solar system, detected by Voyager 2 when it made a flyby in 1986.
Uranus has a number of small rings and 27 known moons. The largest are Miranda, Ariel, Umbriel, Titania, and Oberon, although the Uranus satellite system has the lowest mass of all the outer planets. Miranda has some fault canyons up to 20 km (12 mi) deep and chaotic surface features, suggesting that it may have been completely destroyed by an impact in the distant past, only reforming haphazardly.
Uranus is unique in having the largest axial tilt of any planet in the solar system, 97.77°, meaning that days and nights on some parts of the planet last for decades. Of all the gas giants, it is the most anonymous, although a small dark spot was observed in 2005.
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