William Herschel was born in Hanover, Germany, at a time when the city belonged to England under the rule of George II. As Herschel' s father was a musician in the Hanoverian army, Herschel himself was trained in music in order to enter the same profession. The Seven Years War, however, made military life an unattractive option, and in 1757 Herschel arrived in England, where he began working as an organist and music teacher. Herschel learned of astronomy through his interest in the theory of music and the scientific basis for musical sounds, which led him to mathematics and then optics.
Isaac Newton's treatise on optics inspired Herschel with his desire to study the stars. Unable to find a telescope of a high enough resolution, he decided to grind his own lenses and to design his own instruments; he was helped by his sister Caroline, who came to England in 1772. As Herschel's first telescope, a six-foot (183-cm) Gregorian reflector, was one of the best of its kind, he decided that its first application would be to conduct a systematic survey of the stars and planets. Throughout his life he built numerous telescopes, each one more sophisticated and more powerful than the last.
Herschel's first major discovery occurred in 1781 during his second survey of the sky when he announced the existence of a new planet to be found in the constellation of Taurus. Herschel's name for the new planet was Georgium Sidus, George's star, in honor of King George III, but it eventually came to be known as Uranus, after the mythical father of Saturn. The discovery of Uranus, which effectively doubled the previously accepted size of the solar system, caused a popular and scientific sensation, and George III appointed Herschel to the position of King's Astronomer while providing him with a small annuity that allowed him to pursue astronomy full time.
Herschel's most significant achievements were in the area of sidereal astronomy, to which he contributed the first systematic body of evidence on the order and nature of the stars and the planets. Whereas plenty of theories had been put forward by prominent philosophers of the time on the systems that might govern the universe, none was supported by any scientific gathering of data. In 1783, Herschel began to search for nebulae in the sky, and raised their known total from little more than 100 to 2,500. Much of eighteenth-century astronomy set out to determine the distances between stars; trigonometrical calculations based on their apparent annual movement, however, had failed. Galileo had proposed the use of double stars, pairs of stars very close together, to calculate stellar distance, where the fainter member of the pair was so far away as to represent a fixed point from which the annual movement of its brighter companion could be measured. In Herschel's second survey, he searched for double stars, producing three catalogs over the next 40 years and listing 848 examples. It was later discovered by another astronomer who had seen Herschel's work that these double stars were in fact companions in space held together by gravitational forces and therefore equidistant from Earth; Herschel had assumed that companions in space would have been of equal brightness, and had therefore discounted this possibility. Nonetheless, much of Herschel's work was concerned with producing evidence for the powers of attraction between stars. In three of his papers delivered between 1784 and 1789, he proposed a cosmogony for the universe in which stars, initially randomly scattered throughout the universe, clustered together over time around the regions from which they originally developed.
Herschel was the first to embark upon a scientific study of the Milky Way and half of his work, though less influential, focuses upon the solar system. He studied the Sun, observing that what we see is not the Sun itself but the clouds of gases that cover its surface, and examined the nature of the infrared section of the spectrum by which some of the Sun's heat is transmitted. Besides calculating the height of lunar mountains, Herschel devoted most of his attention to the other known planets, Venus, Mars, Jupiter, and Saturn, determining their rotation period and checking the inclination of their axes, their shape, and the nature of their atmospheres. Herschel devoted most of his attention to examining Saturn and its rings, arguing at one point that the rings were solid, but later conceding that they were in fact composed of floating particles.
Herschel's work on nebulae had led him to conclude that they might well be other solar systems seen only as a luminous cluster of stars around a brighter one. As a result, he saw the Milky Way and Earth as only one rather insignificant part of the universe. In this sense, he changed the status of the solar system within the universe in much the same way as Nicholas Copernicus had Earth when he showed that the planets revolved around the Sun rather than Earth.
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