William Lassell was a British astronomer born on June 18, 1799. He is best known for discovering two moons of the planet Uranus, named Ariel and Umbriel, in 1851. Lassell built his own telescopes and was a pioneer in the field of observational astronomy during the 19th century. In addition to his discoveries, Lassell was also involved in the development of telescope technology. He constructed a large reflecting telescope, which allowed him to make significant contributions to the study of celestial bodies. Lassell passed away on October 5, 1880, leaving a lasting impact on astronomy.