William Herschel

Friedrich Wilhelm Herschel was born on November 15, 1738, in Hanover, then an independent German electorate whose ruler also held the British crown ^[1]. His father, Isaac Herschel, served as an oboist in the band of the Hanoverian Guards and raised his ten children in a household where music was both livelihood and nightly entertainment. Isaac also loved astronomy and philosophy, and the family later recalled long evening conversations about the stars, subjects far removed from the modest circumstances in which they lived ^[2].

Wilhelm joined the Guards band as an oboist at fourteen, following his father and his elder brother Jacob into military music. Formal schooling was limited, but he read widely, studied French and English, and worked through books on mathematics and harmony on his own ^[1]. Any account of William Herschel facts has to begin with this self-education, because almost everything he later achieved in science rested on knowledge he acquired without a university.

The Seven Years' War upended this settled life. After Hanoverian forces suffered defeat by the French at the Battle of Hastenbeck in 1757, the nineteen-year-old musician left the regiment and made his way to England ^[2]. He had visited the country briefly the year before with the band and spoke some English. He would spend the rest of his life there, eventually anglicizing his name to William Herschel.

Herschel spent his first English years piecing together a living as a copyist, performer, and teacher, working in London and then in the north of England. He composed steadily during this period: his output eventually included 24 symphonies, numerous concertos for oboe, violin, and viola, and church music ^[3]. In 1766 he secured the post of organist at the fashionable Octagon Chapel in Bath, the resort town where wealthy Georgian society came to take the waters ^[1].

Bath gave him stability and income. He directed concerts, taught as many as several dozen private pupils in busy seasons, and became a fixture of the city's musical life. In 1772 he travelled back to Hanover and brought his younger sister Caroline Herschel to Bath, ostensibly to train her as a singer. She became his housekeeper, then his assistant, and ultimately a significant astronomer in her own right ^[4].

Music led him to science by a direct route. Studying Robert Smith's treatise Harmonics drew him to the same author's A Compleat System of Opticks, and from optics he moved to astronomy texts such as James Ferguson's Astronomy ^[2]. By 1773 he was buying lenses and hiring telescopes, and when purchased instruments disappointed him, he resolved to grind and polish his own mirrors. The parlour of the Herschel home filled with pitch, abrasives, and half-finished specula, to Caroline's frequent dismay ^[4].

On the night of March 13, 1781, observing from the garden of 19 New King Street in Bath with a 6.2-inch reflecting telescope of his own construction, Herschel noticed an object in the constellation Gemini that showed a small disk rather than a starlike point ^[1]. He first reported it as a possible comet. Over the following months, astronomers across Europe computed its path and found a nearly circular orbit far beyond Saturn: it was a new planet, the first discovered since prehistoric times ^[5].

The find made the Bath organist famous almost overnight. He proposed naming the planet Georgium Sidus, the Georgian Star, in honour of King George III, though continental astronomers preferred Uranus, the name suggested by Johann Bode, which eventually prevailed ^[5]. The Royal Society awarded Herschel the Copley Medal in 1781 and elected him a Fellow, and in 1782 the king granted him an annual pension of 200 pounds to work as astronomer under royal patronage ^[1].

The pension was less than his musical income, but it bought him what he wanted most: time. He gave up professional music, left Bath, and settled near Windsor, first at Datchet and from 1786 at Observatory House in Slough, where he could show the heavens to the royal family on request and otherwise observe every clear night ^[2].

Herschel was the finest telescope maker of his century as well as its most productive observer. He ground and polished hundreds of mirrors, sold instruments to observatories and wealthy patrons across Europe, and steadily enlarged his own equipment ^[3]. His workhorse was a reflector of 18.7 inches aperture and 20 feet focal length, completed in 1783. With royal funding he then built a giant with a 48-inch mirror and a 40-foot tube, finished in 1789; on one of its first nights it revealed Enceladus, a previously unknown moon of Saturn, and Mimas followed weeks later ^[5]. The 40-foot telescope proved cumbersome in practice, but it remained the largest in the world for half a century.

His observing programme was systematic in a way astronomy had rarely seen. Sweeping the sky strip by strip with Caroline recording at his side, he catalogued about 2,500 nebulae and star clusters, published in three catalogues between 1786 and 1802, where fewer than a hundred well-known examples had existed before ^[4]. He also compiled catalogues of more than 800 double stars, and in 1803 he demonstrated that some pairs orbit one another, the first observational proof that Newton's gravitation operates beyond the solar system ^[1].

Herschel thought about the architecture of the whole stellar system. By counting stars in sample fields, a method he called star gauging, he sketched the Milky Way as a flattened, grindstone-shaped assembly of stars with the Sun inside it ^[2]. He detected the Sun's own motion through space toward a point in the constellation Hercules, and he speculated that some nebulae might be distant star systems while others were true clouds of luminous fluid, a question that would not be settled for more than a century.

In 1800 Herschel made a discovery that belongs to physics as much as astronomy. While testing filters for observing the Sun, he noticed that differently coloured glasses passed different amounts of heat. He set up a prism, spread sunlight into a spectrum, and placed thermometers in each colour band. Temperatures rose from violet to red, and, crucially, a thermometer placed beyond the red end of the visible spectrum registered the highest reading of all ^[6].

He concluded that the Sun emits invisible rays lying past the red, which he called calorific rays. This was the first detection of what is now called infrared radiation, and the first evidence that light extends beyond what the human eye can perceive ^[6]. He published the experiments in the Philosophical Transactions of the Royal Society in 1800. Among all William Herschel achievements, this one has arguably had the widest reach: infrared science now underpins astronomy, medicine, night vision, and climate observation, and the European Space Agency named its Herschel Space Observatory, launched in 2009, in his honour ^[7].

In 1788, at the age of forty-nine, Herschel married Mary Pitt, a widowed neighbour whose fortune ended his financial worries ^[1]. Their only child, John Herschel, born in 1792, became one of the most eminent scientists of the nineteenth century, extending his father's sky surveys to the southern hemisphere from the Cape of Good Hope and helping to found modern photography vocabulary ^[3].

The marriage strained his partnership with Caroline, who moved to nearby lodgings but continued to work at the telescope. She discovered eight comets between 1786 and 1797 and received her own royal salary of 50 pounds a year, making her one of the first women paid for scientific work in Britain ^[4]. Brother and sister remained close collaborators until his death.

Contemporaries described Herschel as courteous, tireless, and single-minded about observation. During his great sweeps he would stand at the telescope through entire winter nights, dictating positions and descriptions to Caroline at a window below, and he reportedly kept observing even in freezing weather when the ink congealed in the pen ^[2]. He never lost his Hanoverian accent, and music remained a private pleasure long after he stopped performing.

Honours accumulated in his final decades. He received the Prussian order Pour le Merite recognition among continental academies, was made a Knight of the Royal Guelphic Order in 1816, becoming Sir William Herschel, and in 1820 served as the first president of the Astronomical Society of London, which later became the Royal Astronomical Society ^[1]. He continued observing and publishing into his seventies, including papers on the structure of the heavens and on the nature of nebulae.

Herschel died at Observatory House in Slough on August 15, 1822, aged eighty-three, and was buried at St Laurence's Church in nearby Upton ^[1]. His epitaph there records that he broke through the enclosures of the heavens. Caroline returned to Hanover, where she completed the reorganization of his nebular catalogues, work for which the Royal Astronomical Society awarded her its Gold Medal in 1828 ^[4].

Any William Herschel biography ends with an unusually long list of firsts: the first new planet of the telescopic age, two moons of Saturn and two of Uranus, infrared radiation, the motion of the Sun through space, and proof of gravity among the stars. His nebular catalogues grew, through his son John and later compilers, into the New General Catalogue whose NGC numbers astronomers still use today ^[3]. Craters on the Moon and Mars, a gap in Saturn's rings, the William Herschel Telescope on La Palma, and two space observatories carry the family name. Few careers in science have begun so far from science, and few have changed its map so thoroughly ^[7].