Caroline Lucretia Herschel was a German-British astronomer, whose most significant contributions to astronomy were the discoveries of several comets, including the periodic comet 35P/Herschel–Rigollet, which bears her name. She was the younger sister of astronomer William Herschel, with whom she worked for most of her career. She was born in Germany, and spent 50 years in England, before returning to Germany in 1822.
Transition to astronomy
In the 1770s, as William became more interested in astronomy, he started to build his own telescopes from lenses he had ground, unhappy with the quality of lenses he was able to purchase. Caroline would feed him and read to him as he worked, despite her desire to burnish her career as a professional singer.
She became a significant astronomer in her own right as a result of her collaboration with him. The Herschels moved to a new house in March 1781 after their millinery business failed, and Caroline was guarding the leftover stock on 13 March, the night that William discovered the planet Uranus. Though he mistook it for a comet, his discovery proved the superiority of his new telescope. Caroline and William gave their last musical performance in 1782, when her brother accepted the private office of court astronomer to King George III; the last few months of their musical career had been in shambles and were critically panned.
First discoveries and catalogue
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." 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. 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. She recognized that this work demanded speed, precision and accuracy.
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.
Comets
During 1786–1797 she discovered eight comets, the first on 1 August 1786 while her brother was away and she was using his telescope. She had unquestioned priority as discoverer of five of the comets and rediscovered Comet Encke in 1795. 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." 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.
Caroline Herschel 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. 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. In 1791, Caroline began to use a 9-inch telescope for her comet-searching, and discovered three more comets with this instrument. 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.
In 1787, George III granted Caroline Herschel an annual salary of fifty pounds for her work as William’s assistant. The appointment made her one of the earliest women to receive official payment for astronomical work in Britain. Her independent comet discoveries and extensive cataloguing make clear that this supporting title did not encompass the full range of her scientific achievements.