William Herschel

(From "Voyager at Uranus," 1986, NASA JPL 400-268 7/85)

A professional interest in musical theory, which broadened to encompass a general study of mathematics, preceded Sir William Herschel's passionate interest in astronomy and led to his discovery of the seventh planet.

He was born Frederich Wilhelm Herschel in Hanover in 1738. His father, a bandmaster in the Hanoverian Guards, encouraged him toward a musical career, and Herschel joined the Hanoverian Guards as a musician in his midteens. He moved to England in his early twenties after service in the Seven Years' War. With the goal of becoming a composer, he traveled throughout England working as a freelance musician, music copier, and organist. In 1766, Herschel won appointment as the organist for the new Octagon Chapel in Bath. He was later named director of public concerts for the city.

Herschel read widely on the subjects of harmonics, mathematics, and philosophy. Historians believe the first book he read on astronomy was James Ferguson's "Astronomy Explained Upon Sir Isaac Newton's Principles, and Made Easy to Those Who Have Not Studied Mathematics."

By his late thirties, his dabbling in astronomy had become a more consuming hobby. He put rudimentary telescopes together from scraps and used parts. The more of the sky he saw, the more he wanted to see. By late 1773, when he couldn't afford to buy the most powerful telescope available, he determined to build his own.

Herschel and his brother Alexander and sister Caroline, also musicians, shared a house in Bath. Building William's telescopes became a family affair.

Alexander helped with the construction. "It was to my sorrow," wrote Caroline in her memoirs, "that I saw almost every room turned into a workshop...Alex putting up a huge turning machine in a bedroom for turning patterns, grinding glasses and turning eyepieces."

But Caroline, who would also become a talented astronomer, pitched in as well, even feeding Herschel his meals while he spent hours grinding or polishing by hand a metal speculum, or reflector, for his telescope.

With the best of his telescopes (a 7-foot focal-length instrument with a 6.2-inch reflector), he began what he called "reviews of the heavens" from his garden. Over months of observations, he believed he'd spotted forests of trees on the moon and noted them in his meticulously kept log. He spent many of his observing hours studying double stars and decided to study generally the distribution of the stars and to try to calculate their distances.

While studying stars in the constellation Gemini the night of March 13, 1781, he found a disk-like object moving slowly across the starfield. He believed it to be a comet and reported his observation as such to the British Astronomer Royal.

Within days, however, the object's orbit was calculated as one no comet would likely follow. In addition, it was so distant that, if it had been a comet, it would have been too small to be seen with the instruments of the day.

News of the sighting spread quickly throughout the scientific community. Astronomers and mathematicians across Europe computed the object's approximate size and orbit and, by May 1781, concluded that 42-year-old amateur astronomer William Herschel of Bath had discovered a new planet as far beyond Saturn as Saturn is from the Sun.

Many names were proposed for the new body: "Hypercronius" ("above Saturn"), "Minerva" (the Roman goddess of wisdom), and "Herschel" were candidates. Herschel offered "Georgium Sidus" ("The Georgian Planet" to flatter King George III of England and Herschel's native Hanover. Royal patronage would later support Herschel's work during his distinguished scientific career.) But, astronomy being an international concern and George being an unpopular monarch outside of England and Hanover, variations on his name were vetoed. Astronomers finally agreed upon "Uranus" personification of the heavens in Greek mythology, son of Gaea (Earth) and, by her, father of Saturn and grandfather to Jupiter.

Herschel, continually building bigger and better telescopes throughout his career, also discovered the Uranian moons Titania and Oberon in 1787. English astronomer William Lassell found Ariel and Umbriel in 1851. Herschel's son, John, named all four. They are the only moons in the solar system not called after figures in Greek and Roman mythology. Instead, they are named for characters in English literature: Oberon and Titania are the king and queen of the fairies in Shakespeare's "A Midsummer Night's Dream"; Ariel and Umbriel appear in Alexander Pope's "Rape of the Lock"; Ariel also appears as a spirit in Shakespeare's "The Tempest." Miranda, discovered by the late American astronomer Gerald Kuiper in 1948, is named after Prospero's daughter in "The Tempest."