The 18th century was also a century of great observers. William Herschel (1738–1822), helped by his sister Caroline (1750–1848) built the biggest telescope of the day (40-foot), but did his best work on a 20-foot telescope. There were problems with the mirror of the large one. The discovery of Uranus put his career on the way: he got a salary of £200 a year as "King's Astronomer". He got a rough idea of where we are in the galaxy, and could see other spiral galaxies. He called them "island universes" like the Milky Way. Also he began to work out the motions of different stars. He discovered double stars, and published catalogues of them. Herschel's observations brought astronomy into the modern era.