The other day the news featured a bit about Pluto, and is it or is it not a planet? This is a controversy that goes back a while, and the planet is so far away that it is hard to truly document its path. In 2006, Pluto was demoted, by recent debate says it IS a planet. In the next few months, the New Horizon probe spacecraft, will "visit" Pluto and we will have an answer...maybe.
Anyway, I looked into 18th Century info on the planets, and find the following:
Sir Frederick William Herschel, a German-born British scientist/astronomer first reported the discovery of Uranus on April 26, 1781. It was initially believed to be a comet. He also, in 1787, reported 2 satellites orbiting Uranus, Titania and Oberon. we later reported four more.
From August to November 1789, he noted two moons of Saturn, Mimas and Enceladus.
Herschel became interested in astronomy in 1773, constructing his own large telescope in 1774, spending nine years doing sky surveys. In 1781 he realized that Uranus was a planet and not a star. It was the first discovery of a planet since antiquity, and he himself became a star (celebrity) overnight. King George III appointed him as "Court Astronomer", and he was elected to the Fellows of the Royal Society, and given grants to develop new telescopes.
Later, His catalog of nebulae were published in 1802, including over 2,500 objects flying around "out there", and another 5,000 by 1820. He also discovered the existence of infrared radiation. He was knighted in 1816, and died in 1822. His only son, John, continued his work.