Caroline Herschel

A telescope that William Herschel made for Caroline 1795

William's interest in astronomy started as a hobby to pass time at night. At breakfast the next day he would give an impromptu lecture on what he had learned the night before. Caroline became as interested as William, stating that she was "much hindered in my practice by my help being continually wanted in the execution of the various astronomical contrivances."[12] William became known for his work on high performance telescopes, and Caroline found herself supporting his efforts. Caroline spent many hours polishing mirrors and mounting telescopes in order to maximize the amount of light captured.[16] She learned to copy astronomical catalogues and other publications that William had borrowed. She also learned to record, reduce, and organize her brother's astronomical observations.[17] She recognized that this work demanded speed, precision and accuracy.[18]

Caroline was asked to move from the high culture of Bath to the relative backwater of Datchet in 1782, a small town near Windsor Castle where William would be on hand to entertain royal guests. He presumed that Caroline would become his assistant, a role she did not initially accept. She was unhappy with the accommodations they had taken; the house they rented for three years had a leaky ceiling and Caroline described it as "the ruins of a place". She was also aghast at the prices in the city and the fact that their domestic servant was imprisoned for theft at the time of her arrival. While William worked on a catalogue of 3,000 stars, studied double stars, and attempted to discover the cause of Mira's and Algol's variability, Caroline was asked to "sweep" the sky, meticulously moving through the sky in strips to search for interesting objects. She was unhappy with this task at the beginning of her work, longing for the culture of Bath and feeling isolated and lonely, but gradually developed a love for the work.[7]

On 28 August 1782 Caroline initiated her first record book. She inscribed the first three opening pages: "This is what I call the Bills & Rec.ds of my Comets",[lower-alpha 1] "Comets and Letters", and "Books of Observations". This, along with two subsequent books, currently belong to the Herschel trove at the Royal Astronomical Society in London.[20]

On 26 February 1783, Caroline made her first discovery: she had found a nebula that was not included in the Messier catalogue. That same night, she independently discovered Messier 110 (NGC 205), the second companion of the Andromeda Galaxy. William then began to search himself for nebulae, sensing that there were many discoveries to be made. Caroline was relegated to a ladder on William's 20-foot reflector, attempting impossible measurements of double stars. William quickly realized his method of searching for nebulae was inefficient and he required an assistant to keep records. Naturally, he turned to Caroline.[7][11]

"But it was not til the last two months of the same year before I felt the least encouragement for spending the starlight nights on a grass-plot covered with dew or hoar frost without a human being near enough to be within call."[21]

In the summer of 1783, William finished building a comet-searching telescope for Caroline, which she began to use immediately.[11] Beginning in October 1783, the Herschels used a 20-foot reflecting telescope to search for nebulae. Initially, William attempted to both observe and record objects, but this too was inefficient and he again turned to Caroline. She sat by a window inside, William shouted his observations, and Caroline recorded. This was not a simple clerical task, however, because she would have to use John Flamsteed's catalogue to identify the star William used as a reference point for the nebulae. Because Flamsteed's catalogue was organized by constellation, it was less useful to the Herschels, so Caroline created her own catalogue organized by north polar distance.[7][21] The following morning, Caroline would go over her notes and write up formal observations, which she called "minding the heavens."[20]

During 1786–97 she discovered eight comets, the first on 1 August 1786 while her brother was away and she was using his telescope.[5] She had unquestioned priority as discoverer of five of the comets[3][5][22] and rediscovered Comet Encke in 1795.[23] Five of her comets were published in Philosophical Transactions. A packet of paper bearing the superscription, "This is what I call the Bills and Receipts of my Comets" contains some data connected with the discovery of each of these objects. William was summoned to Windsor Castle to demonstrate Caroline's comet to the royal family. William recorded this phenomenon, himself, terming it "My Sister's Comet."[24] Caroline Herschel is often credited as the first woman to discover a comet; however, Maria Kirch discovered a comet in the early 1700s, but is often overlooked because at the time, the discovery was attributed to her husband, Gottfried Kirch.[8]

She wrote a letter to the Astronomer Royal Nevil Maskelyne to announce the discovery of her second comet. In December 1788, Maskelyne wrote back congratulating her.[25] The third comet was discovered on 7 January 1790, and the fourth one on 17 April 1790. She announced both of these to Sir Joseph Banks, and all were discovered with her 1783 telescope.[26] In 1791, Caroline began to use a 9-inch telescope for her comet-searching, and discovered three more comets with this instrument.[11] Her fifth comet was discovered on 15 December 1791 and the sixth on 7 October 1795. Caroline wrote in her journal during this time "My brother wrote an account of it to Sir J. Banks, Dr. Maskelyne, and to several astronomical correspondents" for the discovery of her fifth comet. Two years later, her eighth and last comet was discovered on 6 August 1797, the only comet she discovered without optical aid.[11][26] She announced this discovery by sending a letter to Banks.[26] In 1787, she was granted an annual salary of £50 (equivalent to £6,800 in 2022[27]) by George III for her work as William's assistant.[14] Caroline's appointment made her the first woman in England honored with an official government position, and the first woman to be paid for her work in astronomy.[4][9]

In 1797 William's observations had shown that there were a great many discrepancies in the star catalogue published by John Flamsteed, which was difficult to use because it had been published as two volumes, the catalogue proper and a volume of original observations, and contained many errors. William realised that he needed a proper cross-index to properly explore these differences but was reluctant to devote time to it at the expense of his more interesting astronomical activities. He therefore recommended to Caroline that she undertake the task, which ultimately took 20 months. The resulting Catalogue of Stars, Taken from Mr. Flamsteed's Observations Contained in the Second Volume of the Historia Coelestis, and Not Inserted in the British Catalogue[28] was published by the Royal Society in 1798 and contained an index of every observation of every star made by Flamsteed, a list of errata, and a list of more than 560 stars that had not been included.[4][11] In 1825, Caroline donated the works of Flamsteed to the Royal Academy of Göttingen.[29]

Throughout her writings, she repeatedly made it clear that she desired to earn an independent wage and be able to support herself. When the crown began paying her for her assistance to her brother in 1787, she became the first woman—at a time when even men rarely received wages for scientific enterprises—to receive a salary for services to science.[3] Her pension was £50 a year, and it was the first money that Caroline had ever earned in her own right.[11]

When William married a rich widow, Mary Pitt (née Baldwin) in 1788, the union caused tension in the brother-sister relationship. Caroline has been referred to as a bitter, jealous woman who worshipped her brother and resented those who invaded their domestic lives.[30] In his book The Age of Wonder, Richard Holmes is more sympathetic to Caroline's position, noting that the change was in many respects negative for Caroline. With the arrival of William's wife, Caroline lost her managerial and social responsibilities in the household and accompanying status. She also moved from the house to external lodgings, returning daily to work with her brother. She no longer held the keys to the observatory and workroom, where she had done much of her own work. Because she destroyed her journals from 1788 to 1798, her feelings about the period are not entirely known. In August 1799, Caroline was independently recognized for her work, when she spent a week in Greenwich as a guest of the royal family.[11]

Barthélemy Faujas de Saint-Fond indicated she and her brother continued working well during this period. When her brother and his family were away from home, she often returned there to take care of it for them. In later life, she and Lady Herschel exchanged affectionate letters, and she became deeply attached to her nephew, astronomer John Herschel.[6][11]

William's marriage likely led to Caroline becoming more independent of her brother and more a figure in her own right.[31] Caroline made many discoveries independently of William and continued to work solo on many of the astronomical projects which contributed to her rise to fame.

In 1802, the Royal Society published Caroline's catalogue in its Philosophical Transactions of the Royal Society A under William's name. This listed around 500 new nebulae and clusters to the already known 2,000.[20] Toward the end of Caroline's life, she arranged two-and-a-half thousand nebulae and star clusters into zones of similar polar distances so that her nephew, John Herschel, could re-examine them systematically. The list was eventually enlarged and renamed the New General Catalogue. Many non-stellar objects are still identified by their NGC number.[32]