William Lassell’s main occupation as a Liverpool brewer made him a perfect astronomer. He had developed a good engineering sense, which came in handy when crafting his precision telescopes; and as a successful businessman he had the requisite downtime to devote to study of the heavens. He was not a professional astronomer — few were in Britain those days — but he was an educated “Grand Amateur”, the kind that filled the ranks of the Royal Astronomical Society.

On this day, October 10, in 1846, William Lassell, observing the newly-disovered planet of Neptune, discovered it had a moon (as well as a ring, which disappeared when the telescope was adjusted). Lassell and his daughter recorded their observations and reported it to the R.A.S. and the newspapers.

Lassell’s large 24-inch telescope, an improvement over his previous 9-inch one, he boasted was one of the most precise instruments ever built. Its lens, too big for polishing by human hands, was instead polished by a machine built specifically for the task by a fellow astronomer. It was used to subsequently discover moons around Uranus, Saturn’s rings, and close observations of Jupiter.