March 16: Caroline Lucretia Herschel

Caroline Lucretia Herschel

March 16, 1750 – January 9, 1848

Caroline Herschel was a German-born English astronomer, the sister of astronomer Sir William Herschel with whom she worked throughout both of their careers. Her most significant contribution to astronomy was the discovery of several comets and in particular the periodic comet 35P/Herschel-Rigollet, which bears her name.

William's interest in astronomy started as a hobby to pass time at night. He took to retiring to bed as soon as he arrived home, taking "a bason of milk" and an astronomy book for company. 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.

William's telescopes gained the attention of many in the field. When comparing observations with the Astronomer Royal, Nevil Maskelyne, William's telescope proved far superior. In March 1781 he made his first observation of what would eventually prove to be the planet Uranus. In 1782, William accepted the office of King's Astronomer to George III and moved to Datchet and subsequently to Observatory House near Slough, Berkshire. The new job proved to be a mixed blessing; although it left him with ample free time to continue his astronomical observations, it also meant a reduction in income and being called upon by the king for entertainment at any time. During this time William perfected his telescope making, building a series of ever larger devices that ultimately ended with his famous 40-foot focal length instrument. Caroline was his constant assistant in his observations, also performing the laborious calculations with which they were connected. During one such observation run on the large telescope in 1783, Caroline became caught on an iron hook and when she was helped off "...they could not lift me without leaving nearly 2 ouches of my flesh behind."

In 1778 William married a rich widow. Although his new wife made every effort to stay on friendly terms with Caroline it seems her life was considerably upset. Through this period she continued her observations on her own, and made many of her discoveries. She later reconciled with the couple, and took great delight in her new nephew, John Herschel.

During her leisure hours she occupied herself with sweeping the heavens with a 27-inch focal length Newtonian telescope and by this means detected a number of astronomical objects during the years 1783 - 87, including most notably an independent discovery of M110 (NGC 205), the second companion of the Andromeda Galaxy. During 1786 - 97 she also discovered eight comets, her first comet being discovered on August 1, 1786. She had unquestioned priority on five of the comets and had rediscovered Comet Encke in 1795. The following year she was granted an annual salary of £50 by George III for her work as William's assistant.

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 due to its having been published as two volumes, the catalogue proper and a volume of original observations. William realised that he needed a proper cross-index in order 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. The resulting Catalogue of Stars 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.

Caroline returned to Hanover in 1822 following her brother's death, but did not abandon her astronomical studies, continuing to verify and confirm William's findings and producing a catalogue of nebulae to assist John in his work.

In 1828 the Royal Astronomical Society presented her with their Gold Medal for this work - no woman would be awarded it again until Vera Rubin in 1996.

In 1835, along with Mary Somerville, she was elected to honorary membership of the Royal Astronomical Society; they were the first honorary women members. In 1838 she was also elected as a member of the Royal Irish Academy. In 1846 at the age of 96, she was awarded the Gold Medal for Science by the King of Prussia.