Herschel, William

(originally Friedrich Wilhelm). Born Nov. 15, 1738, in Hanover; died Aug. 25, 1822, at Slough, near London. British astronomer and optician. Member of the London Royal Society (from 1781) and honorary member of the St. Petersburg Academy of Sciences (1789).

The son of a regimental musician, Herschel was educated at home (music and languages). In 1757 he moved to England, where he became known as a musician, composer, and music teacher. Herschel, who studied astronomy on his own, made hundreds of mirrors for telescopes. Between 1786 and 1789 he built his largest, 40-ft (12-m) reflector with a mirror diameter of 122 cm, for the first time making effective use of a single-mirror scheme (Herschelian telescope). He began observations of the sky in 1773. Among his discoveries were the planet Uranus (Mar. 13, 1781), two satellites of Uranus (1787), their retrograde motion (1797), and two satellites of Saturn (1789); he also measured the period of rotation of Saturn and its rings (1790). He discovered the movement of the solar system through space. In the mid-1770’s he began a series of surveys of the stellar sky by his “scoop method” (counts of stars in selected areas). As a result, Herschel for the first time outlined the general form of our galaxy, estimating its dimensions and inferring that it was isolated in space as one of the stellar “islands” in the universe. Herschel interpreted the compact stellar condensations as actual clusters of stars. This work by Herschel marked the beginning of stellar statistics.

Herschel discovered the existence of binary stars (1803) and compiled three catalogs of double stars. One of his greatest contributions was the discovery of more than 2,500 new nebulas and star clusters (1786, 1789, and 1802). Herschel noted 182 double and multiple nebulas and guessed at the physical connection of their components. He ascertained for the first time (1784) a pattern of distribution of nebulas—their tendency to cluster in layers; the “stratum in Coma Berenices” that he singled out makes up a sizable part of the equatorial zone of the Vaucouleurs Supergalaxy (discovered in 1953). Herschel substantiated (1791) the existence of “true” nebulas—from rarefied self-luminous matter—and advanced the nebular stellar-cosmogonic hypothesis of the condensation of stars and their clusters from diffuse matter, developing it (1802 and 1811) into a conception of the evolution of cosmic matter. Herschel was one of the first to begin the study of the solar and stellar spectra and in 1800 discovered infrared rays in the solar spectrum.

Herschel was assisted in designing and making telescopes by his younger brother, Alexander, a talented mechanic; later he was assisted by his son, J. Herschel. Herschel received a great deal of help in his observations from his younger sister, Caroline Herschel (1750-1848), one of the few women astronomers.