In 1772, William took home in Bath, and was joined by his sister Caroline. On May 10, 1773, at age 35, William Herschel purchased a copy of Ferguson's book, Astronomy, and found interest in astronomy. Consequently, he started to become a skilled maker of the most powerful telescopes of his time: After 1774, ha had acquired skills to make specula mirrors superior to any which had been made before. Moreover, he started to observe the heavens.
On March 13, 1781 William Herschel discovered what he first thought to be a comet, but was later found to be planet Uranus. In recognition of this discovery, he was elected to the Royal Society on December 7, 1781, and awarded an annual grant by King George III of England, which enabled him to give up his carrer in music (in May 1782) and concentrate on astronomy.
On December 7, 1781, the day of his election to the Royal Society, his friend, William Watson, presented a copy of Messier's (and Mechain's) Catalog to William. This catalog stimulated his interest in clusters and nebulae. In August 1782, he started to investigate Messier's objects with his superior telescopes. Soon, he "surmised" (to say it in his own words), "that several nebulae might yet remain undiscovered." After first findings following September 1782, he started his sytematical and extensive survey of the skies visible from his location in England in March, 1783, always assisted by his sister Caroline. After initial trial-and-error attempts, he started with regular, systematical sky "sweeps" on October 23, 1783, with his 18.7-inch aperture, 20-foot focal length reflector, with standard magnification 157 and a field of view of 15'4". He made his next discovery on October 28, 1783: NGC 7184, Herschel's H II.1, a little conspicuous galaxy in Aquarius of 11.2 mag. After about 20 years, he ended up in discovering about 2500 new "nebulae" and star clusters.
As the most renowned astronomer of his time, William Herschel contributed significantly to most branches of astronomy: Besides his discovery of Uranus and his search for clusters and nebulae, he discovered two satellites of Uranus, Titania and Oberon, in 1787, and Saturn's moons Mimas and Enceladus in 1789; he investigated the proper motion of stars and derived the peculiar motion of the solar system toward the direction of constellation Hercules, modelled the Milky Way galaxy from stellar statistics, and speculated about the nature of the nebulae, including a discussion of the possibility of external island universes (galaxies) which had been brought up by Kant. He also contributed to physics (especially optics) and, e.g., discovered the infrared light.