Herschel , Sir (Frederick) William

(1738–1822) German–British astronomer

Herschel, who was born in Hannover, started life in the same occupation as his father – an oboist with the band of the Hannoverian footguards. He moved permanently to England in 1757, where he worked as a freelance itinerant musician until in 1767 he was appointed as organist of a church in Bath. His sister Caroline Herschel joined him in Bath in 1772. He was led by his interest in musical theory to a study of mathematics and ultimately astronomy. Herschel made his own telescopes and his early observations were significant enough to be drawn to the attention of George III in 1782. The king, who had a passionate interest in astronomy and clockwork, was sufficiently impressed with Herschel to employ him as his private astronomer at an initial salary of £200 a year and to finance the construction of very large telescopes. At first Herschel settled at Datchet, near Windsor, but in 1786 he moved to Slough where he remained for the rest of his life.

Herschel's contributions to astronomy were enormous. He was fortunate to live at a time when prolonged viewing with a large reflector could not but be fruitful and he took full advantage of his fortune. He made his early reputation by his discovery in 1781 of the first new planet since ancient times. He wished to name it after his patron as ‘Georgium Sidus’ (George's Star) but Johann Bode's suggestion of ‘Uranus’ was adopted. Herschel's work is notable for the unbelievable comprehensiveness with which he extended the observations of others. Thus he extended Charles Messier's catalog of just over 100 nebulae by a series of publications listing over 2000 nebulae. He not only began the study of double stars but cataloged 800 of them. He also discovered two satellites of Uranus – Titania and Oberon (1787) – and two of Saturn; Mimas and Enceladus (1789–90). He built a large number of telescopes of various sizes culminating in his enormous 40-foot (12-m) reflector. This cost George III £4000 plus £200 a year for its upkeep. The eyepiece was attached to the open end, thus eliminating the loss of light caused by the secondary mirror used in the Newtonian and Gregorian reflectors. The disadvantage was the danger of climbing up to the open end of the 40-foot instrument in the dark. One eminent astronomer, Giuseppe Piazzi, failing to master this skill, fell and broke his arm. It was finally dismantled in 1839 while William's son John conducted his family in a special requiem he had composed for the occasion.

Herschel produced not only observational work but theoretical contributions on the structure of the universe. He established the motion of the Sun in the direction of Hercules and tried to calculate its speed (1806). But, above all, he was the first to begin to see the structure of our Galaxy. Conducting a large number of star counts he established that stars are much more numerous in the Milky Way and the plane of the celestial equator, becoming progressively fewer towards the celestial poles. He explained this by supposing that the Galaxy is shaped like a grindstone. If we look through its short axis we see few stars and much dark space; through its long axis we see a stellar multitude. Herschel was supported in his astronomical life by his sister Caroline. His son John also became an astronomer of note.

Herschel was supported in both his domestic and astronomical life by his sister Caroline Lucretia Herschel (1750–1848). She began as his assistant but eventually undertook her own original research. She observed her first comet in 1786 and went on to detect a further seven. She also discovered a number of nebulae. After her brother's death she returned to Hannover where she prepared a catalogue of some 2500 nebulae and star clusters.

Herschel's son, Sir John Frederick William Herschel (1792–1871), also became an astronomer of note. He spent the period 1934–38 in South Africa, where he cataloged nearly 2000 nebulae and an equal number of double stars, publishing the results of his surveys in 1847.