William Herschel thought he had found a comet when he spotted the green disk of Uranus.
Uranus is the seventh planet located far away from the Sun. It is a gaseous planet which was discovered in 1781, mistaken by a comet but after two years it was accepted as a planet. After decades of observations and only one close visit by a spacecraft, which shows us that Uranus has unique atmosphere.
Atmosphere of Uranus is mostly made up of hydrogen and helium as well as a small amount of methane and traces of water and ammonia. The presence of methane gas gives blue colour to Uranus so we can conclude that Uranus is the planet which was thought first a comet by William Herschel.
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