<P> Uranus is the seventh planet from the Sun . It has the third - largest planetary radius and fourth - largest planetary mass in the Solar System . Uranus is similar in composition to Neptune, and both have different bulk chemical composition from that of the larger gas giants Jupiter and Saturn . For this reason, scientists often classify Uranus and Neptune as "ice giants" to distinguish them from the gas giants . 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 . It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (− 224 ° C; − 371 ° F), and has a complex, layered cloud structure with water thought to make up the lowest clouds and methane the uppermost layer of clouds . The interior of Uranus is mainly composed of ices and rock . </P> <P> Uranus is the only planet whose name is derived directly from a figure from Greek mythology, from the Latinised version of the Greek god of the sky Ouranos . Like the other giant planets, Uranus has a ring system, a magnetosphere, and numerous moons . The Uranian system has a unique configuration among those of the planets because its axis of rotation is tilted sideways, nearly into the plane of its solar orbit . Its north and south poles, therefore, lie where most other planets have their equators . 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 . Observations from Earth have shown seasonal change and increased weather activity as Uranus approached its equinox in 2007 . Wind speeds can reach 250 metres per second (900 km / h; 560 mph). </P> <P> Like the classical planets, Uranus is visible to the naked eye, but it was never recognised as a planet by ancient observers because of its dimness and slow orbit . Sir William Herschel announced its discovery on 13 March 1781, expanding the known boundaries of the Solar System for the first time in history and making Uranus the first planet discovered with a telescope . </P> <P> Uranus had been observed on many occasions before its recognition as a planet, but it was generally mistaken for a star . 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 . The earliest definite sighting was in 1690, when John Flamsteed observed it at least six times, cataloguing it as 34 Tauri . The French astronomer Pierre Charles Le Monnier observed Uranus at least twelve times between 1750 and 1769, including on four consecutive nights . </P>

When was uranus first discovered and by who