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.
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. Herschel's first telescope, a 6-foot Gregorian reflector, was one of the best of its kind, and 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 in the constellation 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 contributed the first systematic body of evidence on the types of objects in the universe, and their relative scales. Plenty of theories had been put forward by prominent philosophers of the time on the overall structure of the Universe, but none were 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. Herchel also devoted much effort to measuring stellar distances, an essential element of determining the true size of the Universe. Galileo Galilei had proposed the use of double stars, pairs of stars very close together, to calculate stellar distances, 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. Herschel's surveyed the sky for these double stars, producing three catalogs over the next forty years that listed 848 examples. It was later discovered by another astronomer who had seen Herschel's work that many of these double stars were in fact binary stars, companions in space held in orbit about one another by their mutual gravity and therefore equidistant from the earth. Herschel had assumed that companions in space would have been of equal brightness, and had therefore discounted this possibility.
In addition to his work on stars, Herschel devoted significant effort to the solar system. He studied the Sun, deducing that what we see is not a solid surface but the diffuse, gaseous solar atmosphere; he also examined the nature of the infrared part of the spectrum, in which the Sun radiates a significant portion of its energy. Herschel's wide-ranging attention then drew him to the Moon (he calculated the height of lunar mountains) and to the other planets, including , Venus, Mars, Jupiter, and Saturn. He studied the planets' rotation periods and the inclination of their axes, and observed their shape and the nature of their atmospheres. Herschel was fascinated by Saturn's rings, arguing at one point that the rings were solid, but later conceding that they were in fact composed of small, discrete particles.
Since Herschel's work spanned most of the known Universe, from the planets to the stars and distant nebulae, he acquired a singular perspective on the Universe as a whole. His 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. With this perspective, he saw the Milky Way and the earth as only one rather insignificant part of the universe, and therefore changed the status of the solar system within the universe in much the same way as Nicholas Copernicus had changed the status of the earth when he argued that it revolved about the Sun, and not vice versa.
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