German-born English astronomer and musician, originally Friedrich Wilhelm. He came to England in 1757, and became an organist. In 1773 William and his sister C. L. Herschel, who had moved to England the previous year, took up astronomy, observing with the first of many telescopes that he made himself. His discovery of Uranus on 1781 March 13 made him famous, and he was appointed private astronomer to King George III. With the king's patronage he was able to build a telescope with an aperture of 1.2 m (48 inches), then the largest in the world. In 1787, Herschel discovered the two largest satellites of Uranus, and in 1789 the Saturnian satellites Mimas and Enceladus. During systematic surveys of the heavens he observed and catalogued many double stars and over 2000 nebulae and clusters; this work was continued by his son, J. F. W. Herschel. His observations of double stars revealed that many are in orbital motion around each other. From counts of the stars in different parts of the sky, he reasoned that the Sun is part of a flattened system of stars which from our vantage point in its main plane we see as the Milky Way. From the proper motions of seven bright stars, he deduced that the Sun is moving towards a point in Hercules. In 1800, using a thermometer and prisms, he discovered infrared radiation.