Key figures: William Herschel, Caroline Herschel (observing assistant and independent discoverer), Alexander Herschel (mechanical support)
Summary
In September 1777, William Herschel relocated to 19 New King Street in Bath and established a private workshop and garden observatory devoted to the construction of precision Newtonian reflectors and systematic astronomical observation. In October 1777, he initiated his first formal astronomical work — systematic observations of the variable star Mira Ceti — and began grinding and polishing speculum-metal mirrors for telescopes of unprecedented optical quality. Over the period 1777–1781, Herschel constructed a series of 7-foot Newtonian reflectors with 6.2-inch apertures and executed four complete systematic sky surveys. On March 13, 1781, using an instrument built in his Bath workshop, Herschel discovered Uranus — the first planet discovered in the telescopic era, expanding the known boundaries of the solar system and revolutionizing observational astronomy.
From Music to Astronomy: Herschel’s Career Transition
William Herschel was born Friedrich Wilhelm Herschel on November 15, 1738, in Hanover, Germany, and emigrated to England in 1757 as a musician. By 1766 he had become organist at the Octagon Chapel in Bath, one of the city’s most prestigious musical posts, while supplementing his income as a music teacher and concert director. His salary and teaching income gave him the financial stability to pursue a consuming secondary interest: the construction of telescopes.
Herschel had built his first reflecting telescope — a 5.5-foot instrument — in 1773, four years before the Bath workshop was established. By the time he moved to New King Street in September 1777, he had already abandoned commercially available instruments as optically inferior to what he could produce himself. His attraction to astronomy was methodological as much as observational: he was drawn to the challenge of constructing instruments precise enough to resolve questions no existing telescope could answer, particularly the structure of the stellar universe and the distribution of nebulae.
The year 1777 thus marks not an origin but a consolidation — Herschel committing professional resources (workshop space, systematic time, a permanent site) to an astronomical programme already underway. His sister Caroline (born March 16, 1750) joined him in Bath in 1772 and served as his primary observing recorder, entering data in notebooks while Herschel’s eyes remained at the eyepiece and his hands on the telescope.
The Bath Workshop: Construction and Method
The workshop Herschel built in the garden of 19 New King Street became the most productive private astronomical instrument shop of the 18th century. Herschel fabricated his mirrors from speculum metal — a brittle alloy of copper and tin — which he cast, cooled, ground, and hand-polished to optical precision. He overcame approximately 200 failed castings before achieving consistently reliable results. A single 7-foot mirror required grinding for up to 16 consecutive hours, during which Herschel could not pause without risk of introducing surface irregularities; Caroline fed him food and read aloud to keep him focused.
His primary working instrument was a 7-foot Newtonian reflector with a 6.2-inch (157 mm) aperture and focal ratio of approximately f/13. The telescope gathered more light than any comparable commercial instrument and was mechanically stable enough to support systematic work across multiple observing sessions. Herschel would eventually construct over 400 telescopes in his career, including instruments of 20-foot and 40-foot focal length, but the Bath 7-foot model produced the most consequential discoveries.
His observing method was systematic in a way that distinguished him from contemporaries. He divided the sky into zones and swept each zone repeatedly, noting every object that differed from a point source (i.e., every nebula, cluster, or extended object). His notebooks recorded position, brightness, and form for each object; the four surveys conducted from 1777 to 1802 ultimately yielded the catalogue of 2,500 nebulae and star clusters that became the foundation for the New General Catalogue (NGC) still in use today.
Systematic Sky Survey Programme
Herschel’s formal sky survey programme began in October 1777 with observations of Mira Ceti, a long-period variable star (period approximately 332 days) whose brightness variation had been known since 1596. Mira’s behaviour required extended monitoring across multiple cycles, training Herschel in the discipline of repeated systematic observation at consistent positions.
His first general sky sweep commenced October 1779 from the New King Street garden, covering the full sky accessible from Bath’s latitude (approximately 51°N). A second survey began in earnest during 1781. These surveys were not casual: Herschel typically worked from dusk to dawn when weather permitted, dictating to Caroline without interrupting his telescope sweeps. The resulting notebooks contain observations of hundreds of objects per night during productive sessions.
By 1781, Herschel had catalogued more deep-sky objects — nebulae and star clusters — than any previous observer, and had begun corresponding with the Astronomer Royal Nevil Maskelyne about his instruments and methods.
The Discovery of Uranus, 13 March 1781
On the night of March 13, 1781, Herschel was conducting a systematic sweep of stars near H Geminorum when he encountered an object that appeared to show a perceptible disc — unusual for a star, which should appear as a point source at any magnification. His observing notes read: “a curious either nebulous star or perhaps a comet.” He initially reported it to the Royal Society in his paper “Account of a Comet,” read on April 26, 1781, as a comet.
Subsequent observations by Herschel and by continental astronomers — particularly Anders Johan Lexell of St. Petersburg, who calculated an orbit in May 1781 — established that the object followed a nearly circular orbit far beyond Saturn, consistent with a planet rather than a comet. Lexell’s orbital calculation placed it at approximately 19.2 astronomical units from the Sun. The discovery expanded the known solar system from six to seven planets and established that the boundary of the solar system, assumed fixed since antiquity, was an observational artifact of instrument limitations.
Herschel named the new planet Georgium Sidus (George’s Star) in honour of King George III. The name did not survive internationally — the convention of mythological naming prevailed when the German astronomer Johann Bode proposed “Uranus” in 1782 — but it secured Herschel’s relationship with the Crown. George III awarded him a pension of £200 per year (approximately £30,000 in 2024 terms) and appointed him King’s Astronomer, enabling Herschel to resign his musical posts and devote himself entirely to astronomy. The Royal Society awarded him the Copley Medal in 1781, its highest honour.
Caroline Herschel’s Independent Contributions
Though trained first as William’s assistant, Caroline Herschel became an independent astronomical researcher of the first rank. Between 1786 and 1797 she discovered eight comets — the first woman to discover a comet — and three nebulae. Her 1786 comet discovery made her the first woman to receive formal recognition for an astronomical discovery from the Royal Society. In 1787, George III awarded her a salary of £50 per year as William’s assistant, making her the first woman in England to receive a government salary for scientific work.
Her cataloguing work was equally significant. In 1798 she published a catalogue of 560 stars omitted from the standard reference catalogue of John Flamsteed, with a second index covering 479 objects — corrections and extensions that astronomers continued to rely on through the 19th century. In 1828, at age 77, the Royal Astronomical Society awarded her its Gold Medal, making her the first woman to receive the society’s highest honour. She received the same honour again in 1835, the year she was elected an honorary member alongside Mary Somerville — the first women admitted to the society.
Key Facts
- Workshop establishment: Relocated to 19 New King Street, Bath, on September 29, 1777; constructed a garden workshop for telescope fabrication
- First formal observations: October 1777 — systematic observations of Mira Ceti (variable star, period ~332 days) launched his professional astronomical programme
- Optical innovation: Hand-ground speculum-metal mirrors; overcame approximately 200 failed castings before achieving reliable precision
- Instrument specifications: Primary instrument a 7-foot Newtonian reflector, 6.2-inch (157 mm) aperture, f/13 focal ratio — most productive astronomical telescope of the era
- Uranus discovery: March 13, 1781 — first planet discovered in the telescopic age; initially reported as a comet in his paper “Account of a Comet,” read April 26, 1781; orbital calculation by Lexell confirmed planetary status, May 1781
- Royal recognition: George III awarded Herschel £200/year pension and title King’s Astronomer; Royal Society awarded Copley Medal, 1781
- Career transition: By 1782, Herschel had resigned all musical posts; astronomy became his sole profession
- Catalogue output: Four sky surveys (1779–1802) yielded 2,500 nebulae and star clusters — the foundation of the NGC
- Caroline’s comets: Eight comets discovered 1786–1797; Gold Medal of the Royal Astronomical Society in 1828 — first woman to receive the society’s highest honour
- Total telescopes constructed: Over 400 instruments across Herschel’s career, including 20-foot and 40-foot focal-length giants
Sources
- Wikipedia — William Herschel
- Wikipedia — Caroline Herschel
- MacTutor History of Mathematics Archive — William Herschel
- Agnes M. Clerke, “The Herschels and Modern Astronomy” — Project Gutenberg
- Science History Institute — “A Giant of Astronomy: William Herschel”
- Encyclopedia Britannica — William Herschel