Its nearly circular orbit led him to a conclusion that it was a planet rather than a comet. Finnish-Swedish astronomer Anders Johan Lexell, working in Russia, was the first to compute the orbit of the new object. I have not yet seen any coma or tail to it." Īlthough Herschel continued to describe his new object as a comet, other astronomers had already begun to suspect otherwise. It is as likely to be a regular planet moving in an orbit nearly circular to the sun as a Comet moving in a very eccentric ellipsis. Herschel notified the Astronomer Royal Nevil Maskelyne of his discovery and received this flummoxed reply from him on 23 April 1781: "I don't know what to call it. The sequel has shown that my surmises were well-founded, this proving to be the Comet we have lately observed. Moreover, the comet being magnified much beyond what its light would admit of, appeared hazy and ill-defined with these great powers, while the stars preserved that lustre and distinctness which from many thousand observations I knew they would retain. From experience I know that the diameters of the fixed stars are not proportionally magnified with higher powers, as planets are therefore I now put the powers at 460 and 932, and found that the diameter of the comet increased in proportion to the power, as it ought to be, on the supposition of its not being a fixed star, while the diameters of the stars to which I compared it were not increased in the same ratio. The power I had on when I first saw the comet was 227. either Nebulous star or perhaps a comet." On 17 March he noted: "I looked for the Comet or Nebulous Star and found that it is a Comet, for it has changed its place." When he presented his discovery to the Royal Society, he continued to assert that he had found a comet, but also implicitly compared it to a planet: Herschel recorded in his journal: "In the quartile near ζ Tauri .
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With a homemade 6.2-inch reflecting telescope, Herschel "engaged in a series of observations on the parallax of the fixed stars." Sir William Herschel observed Uranus on 13 March 1781 from the garden of his house at 19 New King Street in Bath, Somerset, England (now the Herschel Museum of Astronomy), and initially reported it (on 26 April 1781) as a comet. The French astronomer Pierre Charles Le Monnier observed Uranus at least twelve times between 17, including on four consecutive nights. The earliest definite sighting was in 1690, when John Flamsteed observed it at least six times, cataloguing it as 34 Tauri. Possibly the earliest known observation was by Hipparchos, who in 128 BC might have recorded it as a star for his star catalogue that was later incorporated into Ptolemy's Almagest. Uranus had been observed on many occasions before its recognition as a planet, but it was generally mistaken for a star. Replica of the telescope used by Herschel to discover Uranus Wind speeds can reach 250 metres per second (900 km/h 560 mph). Observations from Earth have shown seasonal change and increased weather activity as Uranus approached its equinox in 2007. Voyager 2 remains the only spacecraft to visit the planet. In 1986, images from Voyager 2 showed Uranus as an almost featureless planet in visible light, without the cloud bands or storms associated with the other giant planets. Its north and south poles, therefore, lie where most other planets have their equators. The Uranian system has a unique configuration because its axis of rotation is tilted sideways, nearly into the plane of its solar orbit. Like the other giant planets, Uranus has a ring system, a magnetosphere, and numerous moons. The interior of Uranus is mainly composed of ices and rock. It has the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (−224 ☌ −371 ☏), and has a complex, layered cloud structure with water thought to make up the lowest clouds and methane the uppermost layer of clouds. Uranus's atmosphere is similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, but it contains more " ices" such as water, ammonia, and methane, along with traces of other hydrocarbons. For this reason, scientists often classify Uranus and Neptune as " ice giants" to distinguish them from the other giant planets. Uranus is similar in composition to Neptune, and both have bulk chemical compositions which differ from that of the larger gas giants Jupiter and Saturn. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Its name is a reference to the Greek god of the sky, Uranus, who, according to Greek mythology, was the great-grandfather of Ares ( Mars), grandfather of Zeus ( Jupiter) and father of Cronus ( Saturn). Uranus is the seventh planet from the Sun.
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